Dell E172FPb LCD Monitor (Benq OEM) CCFL Backlight Repair

UPDATE – READ FIRST (3 June 2008)

K, so its been a while since I’ve added anything on this page (and in general for my blog) but theres been quite a few concerns around the use of the replacement transistor by people who I would assume know more then me (i know very little).

I’m glad to say that the 2 fixed LCD’s I use still works so that in itself is good but in saying that, based on some of the comments, I dont want to help someone burn their house down, I love my home and I think you do too :-> . Please only do this at your own risk.

One other thing to note here is that I live in New Zealand, which in general is a bit colder then the rest of the world. The LCD doesnt seem to get too hot here but I would think that cooling is would be a bigger issue elsewhere in the world.

Please read all the comments before deciding to use the replacement parts and if you can get hold of the original parts, Please do!!! I’m thinking that if my transisters go sometime soon, I will end up ordering new ones (the propper parts) from some of the places indicated on some comments.

 To everyone who has made comments, thanks, Its always great to see feedback 

E172FPb beforeBeing the second faulty Dell lcd monitor passing my desk in the last 6 months, I thought I’ll make a posting to describe the successful fix to this guy (and the first one, which is still running good).

The symptoms: When pluged in, This guy fires up just long enough to get past the initial “logo” screen and onto the test pattern (its not plugged into the computer at this stage). After about 2 seconds of being on the test pattern, it turns off, or more specificually, the protection circuits kick in, turning off the backlight. So in this case, the monitor was still working and the LED was indicating that the monitor was on (it was green). A good way to test if it is just the back light is to grab a strong light and shine it onto the lcd, If you can see a dark picture underneath then the lcd is def still working and it should be a pretty minor fix.

So what is this protection circuit? The protection circuit on Lcd’s is generally a way of protecting the actual fluorescent tube from getting overdriven (too much current going through them). So when this protection circuit kicks off, it generally means there is either a short in the tube or a short in one of the components near / on the inverter. unless the LCD is quite old, its usually a short somewhere in the inverter circuits.

So after seeing these symptoms and having seen the excact same on the other dell lcd that I had fixed, I was feeling pretty confident of a good outcome….

Opening up the monitor:

  • Remove the screws holding the Stand in place.
  • Remove the stand
  • Flip the monitor so that the bottom is facing up.
  • Grab a flathead screw driver and use it to ply apart the bottom of the monitor.
  • Now that the bottom is released, Start working yourself u8p the sides.
  • Once the sides are sorted, you should be able to seperate the top without a screwdriver, infact, I found that using a screw driver to ply the top made no difference. I think the top is a unique case….
  • Remove the plastic backing
  • Remove the taped shield
  • Disconnect and unhook the 2 ribbon cables which connect to the lcd pannel from the processor board.
  • Disconnect the cable from the processor board to the front control panel.
  • Remove the front plastic cover (they are cliped around the side to the main panel)
  • Remove the 2 hex nuts by the VGA plug
  • Remove the Metel shield along the side of the monitor (that long glossy metel part, it slides right off).
  • Disconnect the 2 cables connecting the back light from the power/inverter board.
  • unscrew the 4 screws from the side of the panel and remove the back metel plate.
  • You should now have all the plastic parts, the main panel (keep this away from anything / anyone who migth step or damage it!!!) and a metel casing part which holds all the pcb’s, one for the Power/inverter and the other for the graphics processor.
  • Unscrew the earth cable and unclicp the plastic holding the power socket in place.
  • Remove the remaining screws which hold the pcbs in place.

You should now be able to pop out the circuit boards, be careful though, although the power baord would be quite amune to static, the processor board (with the dsp chip) is not! be careful with this board, you want to put it on an antistatic bag or newspaper and not on plastic or carpet (the whole static thing again).

Some photos:

dell_e172fpb_opening_1.jpg   dell_e172fpb_opening_2.jpg   dell_e172fpb_opening_3.jpg   dell_e172fpb_opening_4.jpg   dell_e172fpb_opening_5.jpg   dell_e172fpb_opening_6.jpg  

The Internals:

Dell E172FPb Internal 1   internal_2.jpg   Dell E172FPb Internal 4

The Fix

Faulty transistors to checkLooking only at the power/inverter board, there are a small group of 4 transistors which are used to drive the inverter, these fail easiy and when they do fail, they usually fail in pairs. The main problem with testing these is that you can not test these transistors in circuit, you have to remove them to test them. So start by unsoldering one pair and checking them using a multimeter (more info on testing NPN transistors, click here). if these are good, start unsoldering the other pair and do the same.

dell_e172fpb_fixed.jpgIn my case, I found that there was a short in one of the pairs. The origianl transistors were ‘c5707‘ NPN transistors, which are impossible to get hold of here in New Zealand (they can be found on ebay though if you live in the states), so hunting through the jaycar catalogue, I found something quite similar, the “MJE3055” Transistor. The main problem with this guy is that it has a much bigger casing (TO-220 package) and isnt going to fit nicely into the lcd monitor case….

The first dell I had, I moved the new big transistors to the left of the board and moved the original good ones down to the right, then using some insulation tape  and cardboard to isolate the heat sink part of the transistor from the metel (earthed) chassi case. This worked quite well but I’m always worried about how hot these transistors get and and that the insulation tape wont hold (should have used some better quality tape really) so I thought this time around I’ll try something abit different…

MitresawSo what I ended up doing was taking the case down to the garage and starting the Mitre saw up, Made a nice slit where the inverter circuit lives and ripped out that chunk of metel. Although It wasnt as clean as the first Dell I dealt with, It did mean i had some piece of mind around knowing it will never short circuit again the casing.

I think If I were going to do this again, I would go down the insulation tape route based on the clean finish.

The Result

 Putting the whole thing together and having a working product, Priceless :-)

final_dell_e172fpb_lcd_2.jpg

Dell E172FPb

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128 Responses to “Dell E172FPb LCD Monitor (Benq OEM) CCFL Backlight Repair”

  1. kash Says:

    thanks for making this guide.
    it was really appreciate and really helped me when i was fixing my monitor.

  2. bernz Says:

    Nicely done! Good tips, and helpful details (like recommended alternative parts, etc). Congratulations for making the WWW a better place. :-)

  3. Timothy Says:

    My Benq fp 731 17″ went Black but has a green light so I decided to disassemble it and take a looksie at the power & inverter board I couldn’t see anything burnt like the Cap or fuse board looks good visually. I’m going to yank those transistors and test them hope thats the problem other than the cclp bulbs! Thanks for the info!

  4. syscon Says:

    Yep, Seems to be a comon fault around here, if its based on the same oem (you shoudl be able to tell pretty quickly by inspection) then theres still some hope in it
    good luck and let me know how it goes…

  5. Timothy Says:

    Could the Transformer be shorted causing the transistors to short or the ccfl bulbs has too much resistance which overworks the transformers causing the transistors heat up? It seems this works just like a ignition control module that fires the ignition coils on automobile engine, too much resistance in the secondary (ignition wires) or shorted coil will damage the transistors in the module. I’m thinking ccfl bulbs and transformers with the new transistors. Then you have a new monitor?

  6. syscon Says:

    This is pretty much the story around whats happening to these guys. Transformers themselfs might be hard to get hold of and to some degree, Its really hard to figure out if it is the enamel in the transformers which is melting and causing the shorts without a good ref transformer. One argument here is that by using “better” transistors, even though you may not be fixing the underlying issue, you are renewing life into the dead monitors. The one I have been usung has been going for about a year now so it could die tomorrow or hopefully in a year or 2’s time when LCDs become cheap and worthless… :-)
    For more info, Badcaps has some real good information on what people are discovering around this.

    http://www.badcaps.net/forum/showthread.php?t=1303

  7. Timothy Says:

    The transformers may be custom made for benq for their inverter circuit design, being Malaysian or Chinese built, low quality parts, solder and poorly dip boards. How about building or designing board to power up just the ccfl bulbs by passing the crappy design inverter, a patch board? It’s a throw away monitor world!

  8. syscon Says:

    Yep, have done this before for a much older 15″ monitor at a time when throwing lcd’s away (even 15″ ones) was just unheard of… The one i did pretty much involved using a scanner inverter (I’ve seen people use ones from computer mod kits too). The biggest problem around this was that CCFL tubes have very different electrical charastics (largely dependent on size, but also around ambent temperture, age and other factors) and that the inverters for a lcd have feedback systems to ensure that the correct voltage / current and all are correct (theres alot on the net around the idea of trying to keep the correct current/voltage going when the tube is always trying to “short” and taking into enviroment factors and electrical characters of the tube, aswell as making adjustments for the initial kick start voltage). I would think that even with a funny transformer, its still better then having a basic generic inverter (esp if it has no feedback / protection circuits in place). I guess with this “fix” I have posted, i have relied on the protection circuit to kick in if theres anything wrong (ie, the transformer gets worst) and that the transistor just wasnt built to handle the “situation”. The feedback system may be able to make adjustments to composate for the increased power if the transformer’s windings have minor shorts.

  9. Marcus Nieves Says:

    Thank you for posting such a comprehensive guide. Question, how do I find the transistor part number? I have an Envision EN-5200ei. Also, is a there similar guide that explains how solder on a circuit board? Could I send the board to you for repairs?

  10. syscon Says:

    I have done a quick search for schematics relating to the EN-5200ei and there hasnt been much success :-(
    Transistor part numbers are usually printed on teh device, normally in the form of afew letters (which I think relate to the company that produced or designed the transistor) followed by the code. I have noticed that not all transistors have these markings and if thats the case, you will really need the schematics, but other transistors that look like they have no markings but just they are not printed, instead they are etched into the plastic casing. Soldering is pretty easy to do, just pick up some good quality solder and a low wattage (25 Watt / 30watt) soldering iron and just slowly reapply some additional solder to the joints. every now and then when tehres too much solder left on the iron, clean it on a wet sponge (else u will find u start joining/ shorting out points which get messy to clean). I have done this type of thing on tv’s before and u pretty much just work yourway down teh board. I have NEVER done this to any board mounted IC’s and WOULDNT recommend anyone without propper gear/ experience (normal irons would do more damage then good on these!!!) so best to only resolder what u think you are able to…
    The other thing to note is that I’ve seen heaps of Lcd’s with similar symotons, most are not relating to the transistors, instead, most seem to be relating to bad caps somewhere in the same area so keep your eyes opened, could be a much easier fix then resoldering the board.
    finally, As for repairs, I’m In NZ and I generally dont do repairs, only for myself. My main concern around doing repairs for others is that if anything goes wrong, i have to be the doctor that tells them their device is dead :-(
    oh… and I’ll try and find some good posts around soldering from the web tonight to add to comemnts but there are heaps on teh net in the mean time :-)

  11. syscon Says:

    Hey Marcus, Thought this migth be helpful…

    http://www.eserviceinfo.com/download.php?fileid=21121

    It doesnt have too much info around troubleshooting but it does have the parts list for inverter/power board. See if its the same model as what u have :->

  12. Stew Says:

    syscon,
    Great info. I was able to diagnose the problem on a Dell LCD, got the transistors off of eBay (they wern’t available at local Electronics supplier), soldered them onto board and also re-soldered the transformer connections as specified by the transistor supplier fm eBay.

    It works now. Total cost: about $16 (bought 4 transistors but only used 2). Labor, well, what else are you going to do in the evening?

    Thanks for this post. I really appreciate the info.

  13. Bill Says:

    Thanks for the excellent cook book recipe for the DIY repair. I picked up my dead Dell monitor off a neighbour’s pile of discards put out for the quarterly Council rubbish collection last week. Scores of CRTs being discarded every time there is a Council collection, but this was the first LCD monitor I’ve passed, so chucked a u-turn and snagged it. Googled the model number and your document popped up. Yeah, thanks again…

    I bought four MJE3055 transistors from Jaycar here in Sydney; at AU$1.70 each I didn’t bother to test the C5707 originals first. As long as I was desoldering all four to test them I reckoned I’d just replace them all. Two tested OK, but the two bad ones had definite heat damage evident. As you described, the real time and effort expended is actually in trying to fit the oversized new ones into a space not designed to accomodate them.

    I half-way reassembled the screen and plugged it in, beauty – worked a charm. Finished putting the case and stand back on and watched little wisps of smoke emitting from the repaired area after about five minutes. I unplugged the power and took it all apart again to look for heat damage. Nothing seemed over-heated to touch, except the new trannies, so I buttoned it up again and watched it bounce the test pattern around for a couple hours. I couldn’t try it connected to a PC because the neighbour hadn’t discarded the cables and up until now I’ve only had CRTs with permanently attached cables at my house.

    Last night after work I plugged it in to admire my genius and after a few minutes the bouncing test pattern was replaced by a Dell splash image in the centre of the screen flashing every few seconds. I turned it off and back on to find the 2 second display and black screen thereafter, back to the original symptom. Cracked it open and found the trannie closest to the edge of the PCB was showing signs of overheating, unsoldered it to find it shorted. I had installed it bent over the rectangular component next to it to avoid the metal shield and it had melted the closest edge of the item. This must have been the source of the smoke whisps.

    I’m not an EE, but from what I’ve found re the badcap issues, I’m suspecting that I should replace the caps in the vicinity. The fact that the monitor had only been plugged in for a few minutes, then seemed to die only when I punched the power button twice to bring back the bouncing test pattern leads me to suspect the cause to be in the power-on stage during the initial surge of current. My understanding of the purpose of the capacitors is that they buffer the initial power-on surges. But I’m also going to have a closer look at the transformers and their connections. None seems to be overheating, nor is any single transformer warmer to touch than the others, from my earlier checking when the smoke first appeared, so I’m not convinced that I’ve got a shorted winding to find and fix. This should keep me off the streets and out of the pub for a few nights, yet. I’ve also got a dead Compaq Presario identical to the one in your badcap repair article that I’ve suspected was just a capacitor replacement project waiting for me. With two cap replacement projects on the kitchen bench I guess now’s the time visit Jaycar and bring home a bag of caps.

    Now, just a couple days researching which brand of caps is the best value…

    Again, thanks for taking the effort to document the procedures for the rest of us. Meanwhiile I’m keeping my eyes out for more of the Dell monitors that are now past their three-year warranty period. They should start turning up along with the old CRTs in the discard piles put out for Council pickups.

    Cheers,

    Bill K. in Sydney

  14. Thomas Says:

    what is the power dissipation of the c5707. I can not find it so I will try to fit another one it comperable to the c5707.

    Thanks!

  15. syscon Says:

    Hey Thomas, try this url… http://www.datasheet4u.com/html/C/5/7/C5707_SanyoSemiconDevice.pdf.html

    If you find a good replacement, please let us all know :-) cheers

  16. Monitor Doctor Says:

    The C5707 or 2SC5707 transistors that fail in the DELL E172FPb and DELL E173FPb are available at http://www.lcdrepairparts.com and on ebay: http://search.ebay.com/_W0QQsassZtomezak1234?satitle=e173FPb Either option is very reasonably priced and they ship worldwide! MOST IMPORTANTLY they provide the very simple steps necessary to prevent C5707s from failing again, replacing them with heaftier transistors will NOT solve the underlying problem here!

  17. Steve Says:

    So I am having this same problem; however, i’m not familiar with how electronics, in general, function and I don’t feel comfortable trying to fix this on my own. Is this something that is relatively affordable if i were to have a professional fix? Or am I better off just getting a new monitor?

  18. syscon Says:

    Hey Steve,
    This is really just my point of view but Lcd’s at teh prices they are today (and with their better warranty / dead pixles policy etc), its prob better to not get it repaird (they usually charge a big enough fee to took at it which alone makes it not worth it). If you haev any skills on a soldering iron or have a friend who has steady hands, i would highly recomend you give it a shot yourself. usually if you take the careful/ new approch, you will not damage anythign … Theres been quite afew comments on what transisters to use to replace the faulty ones with. I would strongly recomend replaceing them with the “2SC5707 ” if you can get hold, of them, it would work better and ofcourse it would be easier to replace. They are avaliable all over ebay or on online shops and they fit correcly. I should really state for everyone else that this article with using a alternative transister is not ideal but it wors for me and I didnt think spending $20 on international postage was all taht worth it for an old lcd but if you do have access then you shoudl get teh correct transisters (they are cheap enough too). I i were you, I would give it a try, it w2ill give you a sence of achievement knowing you didnt have to trow the lcd out assuming all goes well :-)
    The one thing to watch out for being new and all is that you use a low wattage solder iron (say 15W – 25W) to ensure you dont burn off (they peal off with too much heat) the copper tracks on the board which holds the parts inplace. Also, If you want to increase the chances of success at the trade off for afew more $$$ then I would buy 4 of the 2SC5707 and instead of desoldering the old transisters, i would just cut the legs off them and then desolder whats left of the legs (makes things a bit easier and reduces the risk of burning / ripping off the tracks)

  19. Dirk Jan Luiting Says:

    great work!
    initially, i found an other page about this problem with the 5707,
    (read elswhere one could use a 5706),
    went to my local electronics store in stockholm, elfa….
    they sold me the wrong transistor, much to small.
    my gut feeling allready sayd too small, but placed them just the same, failed…

    now, sitting with their catalogue in my lap, searching for your 3055,
    i found it, and it is making my day!!!!

    great posting!

  20. syscon Says:

    Glad to see it worked :-)
    The one thing to note is that the MJE3055’s do get really hot so they really shoudlnt be against another device (i think that migth be the cause of some issues with another reader). But in saying that, my lcd’s been up for atleast 1 1/2 years (average use, not on 24/7) now with this fix so if it died tomorrow i wouldnt feel all that bad.
    Still for anyone reading, if u can get hold of 5707, try them first :-)

  21. Carl Says:

    Wow it works. This page was amazingly well done. My work was throwing this monitor out so I thought I would take a look at it to see if I could do anything with it. I did the flashlight test and the results were the same as you metioned. I was able to get the ( 2SC5707) Transistors from a company in the United States called Bluestar International Components (http://www.bluestar-online.com/2SC5707_p/2sc5707.htm) and I was able to purchase them on line, they made it very simple. I installed 4 new transistor by following your instructions and presto, it worked. Thank you so much for taking the time to put together such an easy to understand guide. I was a little shakey with the soldering though. Thanks Again.. From, Carl Ontario, Canada

  22. TR Says:

    Using the monitor after repair to write this reply. Found two transistors shorted, ordered new off of eBay – easy repair. Now my question – I have another Dell E172FPb – when turned on it is snow white, no picture, could the same repair fix this problem?? Thanks again, TR

  23. syscon Says:

    Hi TR,
    Glad to see you had success with the first monitor.
    The problem you are having with the second monitor sounds very unrelated to the backlight issue. I dont have much experience with the problem you describe, I’ve never actually managed to fix any monitors with such a symptom, however, the way that LCD’s work, I’m guessing it has more to do with the processing parts of the monitor, where it isnt actually sending the signals to the lcd panel (From observation, Lcd panel seems to let light through on default and you can see very strange effect where the picture fades to white if you manage to disconect power to the lcd monitor but leave power to the lamps). Sorry getting side track…
    If you wanted to test if this is the fault (but with a small risk to the first monitor in the name of proof) you can swap the smaller board on the second monitor into the first monitor which is now working. If you see the same result on the first monitor then that may lead to the conclusion that it is the small board thats faulty and therefore you can focus on that (though if its the main chip on the small board then it most likely wouldnt be worth fixing unless you can find more broken monitors suck as the same model with a cracked screen)…
    By doing this test, I dont think theres much chance that you would damage the first monitor as you should be able to replace the board back and have it in its original state (assuming that it wont damage the power supply etc), however, risk has to be stated….
    Best of luck

  24. Tony Wilson Says:

    I just picked up a Dell E172FPB monitor from a relative. It also blacks out after 1/2 second. But I can’t see anything with a strong light. I can turn it off then on again and the picture will return for 1/2 second. Just long enough to move the cursor ( about 5 power down cycles) to shut it down. Would this be the same problem?

  25. syscon Says:

    Hi Tony, It def sounds like it “could” be the same issue and at the expense of afew $$$, I would still give it a try anyway. If you are in the US, I would think ebay or one of the other places listed by a few other comment posters would be a good source of these parts (aim for the 2SC5707 ones first before looking for alternatives). Also, I had read on other places that applying a tiny bit of fresh solder around some of the circuit joints may also healp (but only around the thich tracks as if trying to do it on teh thinner tracks and not being as skilled on teh soldering iron, you may cause more damage then good, ie: short circuits).
    I would try the flash light thing again though, there really should be a faint image (really faint), maybe best to get to a screen where there is movement and bright colours (like watching a lbright coloured cartoon on you-tube or something).

  26. Tony Wilson Says:

    Thank you for the info. I have already ordered a 4 pack of the 2sc5707 transistors. I was hoping some one would tell me what some of the suppliers are telling people what to do to keep from having to replace them again. I think it had something to do with re-soldering the transformer connections but I don’t know. I am A retired electronic tech. but there were a long time after I retired. I starter as a tube type tech. If there is any more help available I can sure use it. Thank you very much again! I also refuse to order from any one that charges excess freight. I will do without first!

  27. henry Says:

    @syscon: I have a dell 1703fps monitor where the blacklight gets dark after 2 seconds, then when something changes on screen the blacklight goes on again, after a splitsecond it’s off again, this repeats itself over and over again… any idea what the problem is? Problem also is the printboard is much different, it has a seperate inverterboard with 8-legged smd transistors on it…

  28. Tony Wilson Says:

    The c5707 replacement worked. I don’t know for how long since I didn’t re-solder many other joints for I could only find my chisel point tip and was afraid I would short out some points. It is working for now. Thank you very much!

  29. Ken Says:

    Awesome man thanks for all the help. I bought a new monitor already which sucks but now ill be able to run dual with my 8600gt.
    -Hey you know where i could get any transistors,who sells?

  30. syscon Says:

    Hi Ken, theres been a few places mentioned in comments. I prob should really update the blog with afew links so its all contained in one place (i’ll do that tonight), but for now…

    http://www.lcdrepairparts.com

    http://www.bluestar-online.com/2SC5707_p/2sc5707.htm

    http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=C5707&category0=

    Let me know how it goes :-)

  31. syscon Says:

    Hey there henry, Having a quick look for the schematics for that monitor but couldnt find any :-(
    Theres a few different images on the net about the inverters these use but I dont have any experience with these, the only monitors I have had a chance to play with are the ones that usually get thrown away by people I know (I’m not actually a electronic tech so I should emphesise the “play” bit).

    Anyway, Theres a few url’s of places which sell inverters that claim to be for these. They do seem on the expensive end considering the cost of new LCDs. Best advice at this stage is perhaps to look for the parts on your existing inverter which are cheap / easy to replace (things like caps etc cost like afew cents etc). If your one is similar to teh one on the ebay link, I would try replacing the main filter cap (the black one), the 2 greencap caps (I think they are greencaps, anyway, the redish ones) and if still nothing…. i would try the transisters around the caps (the guys towards teh center of the board (with 3 legs on one side and a tab on the other). This is all assuming that the cost of these parts are cheap and that you are willing to take a risk and atempt to fix it. There may be something very obvious that is wrong and you may spot it by just opening them up (things like caps that look like they are leeking or about to explode (I had one in an inveter that had a MKT looking cap with a tumour looking thing comming out of one side and ocne that was replaced… all good)…

    Links:

    http://images.google.co.nz/imgres?imgurl=http://www.lcdpart.com/images/li2070.jpg&imgrefurl=http://www.lcdpart.com/Products/li2070.html&h=178&w=600&sz=36&hl=en&start=2&um=1&tbnid=brwWEk9ZeUFPtM:&tbnh=40&tbnw=135&prev=/images%3Fq%3D1703fps%2Binverter%26svnum%3D10%26um%3D1%26hl%3Den

    http://images.google.co.nz/imgres?imgurl=http://thumbs.ebaystatic.com/pict/2500003184254040_1.jpg&imgrefurl=http://search.express.ebay.com/items/Dell-LCD-Monitor_W0QQ_nkwZDellQ20LCDQ20MonitorQQ_pgnZ7&h=42&w=140&sz=4&hl=en&start=1&um=1&tbnid=h2-d1yV8EQ4vyM:&tbnh=28&tbnw=93&prev=/images%3Fq%3D1703fps%2Binverter%26svnum%3D10%26um%3D1%26hl%3Den

    All the best and let me know how u go, Would love to have a link to your page if u manage to fix it :->

  32. Ken Says:

    Alright thanks man,i already checked ebay and shipping is like way high(since im gona replace all 4 trans. and they charge ship. for each),lcd repairs and bluestar are about same like 15 bucks so ill prob. get from one of them. Thanks again, i don’t think i would have ever solved the problem without your help,good luck out there and lots… :)

  33. John Says:

    Here is a blurb from the badcaps forum with a part number from Radio Shak. Here in the States, there is one about every 20 miles or so, and the parts are usually in stock.

    I have my E172fpb apart to check the transistors. One pair is shorted, so I went to Radio Shack to see about parts. Their part # TIP3055 seems to be what I wanted. The label on the transistor is actually MJE3055, like what Dockarl has used. They are priced at $1.79 each. I think that I will replace all four instead of just the pair that are shorted.

  34. John Says:

    Here is the link to the part:

    http://www.radioshack.com/product/index.jsp?productId=2062611&cp

    and to the blurb that I quoted:

    http://www.badcaps.net/forum/showthread.php?t=1303&page=7&pp=20

  35. Mohammed Says:

    hi Syscon,i tested the transistors but they are all ok.I have a dell 152fpb which behaves exactly the same as u described, what could be the problem if its not the transistors?
    I also tested the white cubes labeled 1j100 in between the transistors and they all shot, is that ok?

  36. Tkniques Says:

    Just wanted to say good work on the writeup. I just fixed my monitor by following
    your instructions.

  37. Rob dR Says:

    Henry, I also have a smoked 1703FPs and I found a bad transformer on the inverter board. It was throwing sparks out the bottom of it and only found it after seeing the sparks and smoke. I found the whole board on e-bay for 39.99 with shipping of 9.00. I haven’t decided to buy it yet though, when you can buy brand new 17″ monitors for $80.

    Good luck.

  38. Kash Says:

    hi again
    i have a problem with my dell e172fpb
    i replaced all 4 bad transistors with new c5707 ones… but im still get the initial sympton as you described.
    green power light is on throughout (not flashing)
    but cannot see anything on screen… ie: the backlight circuit has kicked it.
    if i use my cameras flash i can see the test pattern bobbing up and down, so its working, but its not displaying anything like it should..
    i tried ther board on other dell e172fpb lcd panels, and it has the same problem, so its definetly the board not the lcd screen itself.
    what could still be causing the problem?

  39. Tkniques Says:

    Just wanted to say my fix using 4 new 2SC5707’s blew out after about a week. I re-replaced them with 4 TIP3055’s (appears to be same as MJE3055) from Radioshack. Hopefully this time the repair will hold. Someone correct me if I’m wrong in my logic but hopefully the larger packaging will dissipate heat better and possibly help keep the repair from blowing out again. I also turned down the brightness all the way, but I’m no electrical engineer so I don’t know if that will actually help any. (any input?)

    The new ones are bigger so I ended up having to cut some of the metal housing like in the pictures above.

  40. Dilip Says:

    In reply to Mohammed’s question about the capacitors:

    He wrote “I also tested the white cubes labeled 1j100 in between the transistors and they all shot, is that ok?”

    The word shot can mean anything depending on what you think is correct :-(

    These White cubes are capacitors (from the looks – Polyester caps). If you are checking them outside the circuit, they should not show shorts. If anything, they should show an open circuit. With very high input impedance meters you may see a brief reading as the capacitor is charging – then open.

  41. syscon Says:

    Hey Tkniques, I would have thought the same logic, however, the MJE3055 do get really hot (like heaps hotter then the 2SC5707’s) so thats why I would have thougth original parts would be better. But cos they were not easily avaliable, i used my MJE3055. Give them ago, they have lasted me over a year or so and sill looking good.
    Careful with the TIP3055’s, you woudlnt want to ground it on the case (i cant remmeber what teh case of the TIP3055’s were but its case should not directly touch the case of teh monitor.

  42. syscon Says:

    Hey Kash , i have read on the badcap’s forum that replacing the transistors isnt always teh fix. oftern the transformer is damaged, this may the the cause of what you are having. If so, I dont know if its really economical to pay for a new transformer (not knowing how much they cost but expecting more then its worth)

  43. Hoopzz Says:

    Just reading all your comments ( well some ) the transistors you are all referring to are available in New Zealand, i have been using them in Dell, Benq & Phillips etc… lcd monitors for years with very great success, my stocks are now starting to run low but i am about to order a few more in and if any one is interested I could part with a few or order more in to suit the demand, and they would cost out at about $6.00 NZ ea plus little or no freight, a we bit dearer than the alternatives suggested here but the right ones and no mucking about, and they will also replace the 2sc5706’s.
    None i have fixed have failed yet that i know of, if all bad joints a re soldered properly and transistors replaced and some times the fuse at location PF751, you should get at least another 3-4 years use out of it. Some times it is a bad connection or arcing wire on the ccfl its self but that is very rare.

  44. Dilip Says:

    For people in a situation similar to Kash’s, if the usual fixes don’t work (and the LCD itself seems to be working), it may be a better solution to just get rid of the Backlight tubes, disable the invertor (thus saving the power supply from any loading from that circuit) and replace the backlight with LEDs. The solution is a bit involved but should be a permanent fix. I found at least one example of this being done. Check out:

    It should be possible to feed the LEDs from the monitor power supply itself. Goldmine has some 10,000 mcd LEDs for $0.50 each. It may be possible to use SMD LEDs for skilled people. Another bonus with this technique is that one doesn’t have to deal with high voltages. I checked the specifications on some CCFL lights. They seem to need higher & higher voltages proportional to their length. For about 17″ length, they need over 1700 volts to strike and about 760 volts while running.

  45. Hoopzz Says:

    Sounds like Kash’s problem is the 3 amp fuse that looks like a power diode at location PF751 easy enough to check with a multi meter.

  46. Dilip Says:

    I had three links in my message. Don’t know what happened to them. Trying again with just one first:

    http://hackedgadgets.com/2007/02/18/lcd-monitor-backlight-to-led-conversion/

  47. spilster Says:

    yeah this guide is quality and much in the interests of environment protection and pro ecology. these industrial manufacturers are literally taking the piss out of the world and it’s resources with expensive complex CRT monitors costing millions in man and machine labour, using a vast amount of power, time and energy to end up being obsolete and worth under a quid a piece! yeah we need to save the tft’s and lcd’s as they have cost the earth a lot of resourses (don’t under estimate the amount of work involved making machines like this. check the link to see the making and components in the simple ‘disposable’ lighter)

    http://www.bicworld.com/inter_en/lighters/how_is_made/index.asp

    to chuck them in the bin like a disposable lighter is bad. these makers need to account for sustainability. to churn out disposable crap at an ever increasing rate is sick… sick for mankind! companies that make products like these should be required by law to recycle every piece.

  48. syscon Says:

    you know spilster, I migth not word it like that but I totally agree. The cost of consumer products never seems to account for the enviromental costs, esp the cost of disposal of the product. If it only takes a few extra $$$ to fix a product and not have to throw it away into the dump (these have a whole lot of dangrous chemicals in them, for example, the solder may have lead, the CCFT have mercury etc) then I think its well worth doing. I know that oneday soon these LCD’s are going to die on me and theres not to much I can do about that but the longer they run for, the better it is for the planet and the better it is for my pocket too. I think that if you are going to throw away the screen, you might as well try and fix it or pass it on to someone who might be able to fix it for themselfs (if they cant fix it, i’m sure they would either find parts they can use / keep, turn it into a display in a furniture shop or gain some knowledge out of the whole experience that maybe they are able to fix the next one that passes their way…
    I love your thinking and wish theres more people who thought like u, keep doing whatever bits you do to help save the enviroment. Products should not be made disposable unless they are bio degradable.

  49. john Says:

    Thanks for the tip. Worked like charm. Saved me a couple buying a new monitor.

  50. Maximus Says:

    Hi, i dont know if this is the same problem but it is annoying me very much.

    My monitor is a “didi-t” “LM17A” no doubt a cheap model.

    The problem probably first started about a month ago and has got progressivley worse by the day. What happens is when i turn on the monitor it works fine for about 30 secs and then goes to a blank (all white) screen, so i switch it off and back on and it stays on for about 15 secs and then blank again….5 secs….1 sec……1 sec. …..1 sec…..aghhhhh!! Then eventually after about 5 mins of doing that on and off process, flickers and stays on for the whole day if i need it no problems. As say its getting worse by the day and taking longer and longer to turn on and driving me more and more mad.

    Would this be the same problem for me to have to replace a component or is it likley to be a loose conection somewhere, which i can resolder.

    Ive checked all the cables and graphics card by the way.

    Any help would be muchly appreciated.

    Many thanks

  51. syscon Says:

    I did some search on the “didi-t” “LM17A, doesnt appear to be much information on it :-(
    I would first consider taking it back under warranty (or any other way such as “not fit for purpose” etc) before trying anything on it. Try contacting the manufacture directly. if you cnat find teh manufacture, look on the monitor for a fcc Id and punch it into the search site http://www.fcc.gov/oet/fccid/help.html (also post here too if you can for reference)

    If unable, and its going to end up at the tip anyway, I would try opening it and looking for anythign that looks out of place. http://syscon.wordpress.com/2007/01/27/aoc-lm722-lcd-repairs/ may provide some help, Someone with a AOC which had a different model number found that replacing some caps helped him out and I think I got luckly when replacing the cap on my AOC cos it was so badly damage that I knew straight away that it would be part of teh cause (as it turns out it was the whole cause) so try that….

    worst comes to the worst, I would sell it on ebay, see if someone could use the parts or fix it themselfs, still better then the tip and it might help pay for a new monitor.

    Let me know how it goes, fingers crossed and all :-)

  52. Maximus Says:

    Thanks for the advice. I will let you know how i get on.

  53. Dilip Says:

    Hi Maximus,

    From what you have described, my thought process goes like this:

    The blank white screen – means it is not a problem with the backlight like the E172FPB we are talking about. It is something to do with the controller.

    It works for 30 seconds first , then progressively the working time diminishes to 15, 5, 1 etc. – indicates that this is heat related. Something gets hot and that causes the problem. Letting it cool between turn-ons lets you get back to a working stage. Compound it with the fact that even after leaving it on for a day, you are able to get it to work again (for a few seconds at a time) – indicates that the problem is not a thermal runaway kind that would distroy the components.

    So I have couple of suggestions for you to try. If you could open it in a way to be able to see the controller part of the circuit while you turn it on, that would be ideal. One of the techniques for troubleshooting heat based problems is to force cool suspect components to see if your circuit starts working again. There used to be special spray cans available to spot cool parts of the circuits. Even a compressed air can should work (using the canned air bottle upside-down ). Let the monitor stop working. The go over the circuit board with the can in a pattern that cools one area at a time. If the monitor starts working when you are blasting a certain area, you have localized the problem to components in that area. Now study the components in that area for obvious signs of heat damage. Even look at the soldering with a good magnifying lens under bright light. You may find an intermittant or a bad part this way.

    Touching up the soldering in that area and replacing suspect components are the next steps.

    Good luck.

  54. syscon Says:

    Dilip, Great writeup and good advice, thanks for that :-)

  55. rob Says:

    thorough and clear AND PIX!!!!
    thanks!

  56. Jim Says:

    The 4 required Transisto can be found at Farnell.com. Their part number is 1554597, and they are £0.91 each.

    Thanks also for taking hte time to wrte this out, i’ve waited so long to find a solution that workd.

  57. Sunny Yeung Says:

    I just following your information to repair my monitor, then my monitor now is reborn, Thank so much.

  58. Colin Says:

    there is some great information here, I have one of these monitors and it seems to have just developed a similiar fault, I turn it on, the screen and green light come on for a second then both go out and then the green light starts flashing and each time it flashes on the screen starts to light up slightly but they only flash on for a fraction of a second…they continue flashing.
    Could it be the same problem? thanks in advance for any opinions or insights

  59. Tom Says:

    hey if i get 4 new ones can i just replace all four rather then bother testing the old ones??????

  60. David Says:

    Hi
    great fix,i did all you did and still same problem
    cant confirm (memory going) but i think my green led stayed on test pattern showed after 4-6 seconds of test pattern screen went black.
    Stripped screen down and removed backlights with plans to fit white led, apon removing lights and hanging them on a nail wall one fell down,found the white wire going along tubes one was broken(heat, blackened/burnt) and had come away from end of tube,resolder it and all good now,and have orig transistors in place too

  61. ajaks Says:

    Hey y’all,

    Found your blog. What a stroke of luck! You seem to have nailed the problem with my Dell LCD #E173FPc. It will power up, but blinks off immediately, giving me only a glimpse of the Dell Logo. Then at regular intervals, it will blink on for a fraction of a second — then off again. This process will repeat forever, apparently.

    I discovered that if I heat the thing with a hairdryer set on high pointed into the vents on the back, it will eventually come on and stay on until I turn off the computer. That solution is no longer yielding good results, i.e., it takes longer and longer to get it up and working. So, I’ve given away my secret …. I’m strictly a low tech electronics idiot. Would like to give the repairs a shot though. Any thoughts? Should I just buy the transitors and a soldering iron and start to work? I live in the US of A, so may have access to the parts mentioned. Thanks!

  62. tattoum Says:

    hi, to all
    i have a benq fp767 monitor that when i turn it on it works perfectly for 1 or 2 seconds then it becomes black and after some seconds it flashes for a 1 seccond then black again, and every timer i turn the monitor off then on it does the same thing. the green led is on and i can see the picture so its a backlight problem, i test the 4 c5707 and the 2fu9024n they are all ok. now i dont know what to do and what to check else please help me to repair it.
    thanks to all helpers

  63. Jim in US (Ohio) Says:

    Definitely not “JUST” Another webpress.com weblog. Incredibly clear for such a technical topic, including all of your replies to other readers’ questions and such. You certainly have a talent for explaining the fuzzy stuff…..Thank You very much.

  64. Frightened Says:

    Okay, DO NOT USE the MJE3055 to repair this monitor. That it works is a testament to the relative hardiness off the transistor. That it’s going to burn your house down sooner or later because you’ve overdriven it and it’s caught fire is pretty much a given. There isn’t enough room to adequately cool it in the space available, and adding a fan isn’t going to help you any because there isn’t enough cool air available in the space. The 2SC5707 is a HIGH FREQUENCY design, which trades off current delivery so that it can switch very quickly. The MJE3055 is a GENERAL PURPOSE (ie. it can do “everything” but does nothing well). In Australia/NZ you can get 2SC5707 from http://www.wescomponents.com/ for about $2 AUD each, which is much better than burning your house to the ground!

    Oh, chopping pieces out of the metal shroud voids the monitors r/f emission controls and you run the risk of getting fined by your local broadcast regulators.

    Incidentally, the monitor you’ve shown there is made by BenQ for Dell. Searching on BenQ repair techniques would have turned up all the info you’ve published. You’ll need to resolder practically every joing on the secondary side of the PSU to guarantee your repair works.

  65. Taffy Says:

    Hi syscon, Wonder if you can help me with a Benq fp767?
    The monitor takes 20 to 30 min to turn on and now it wont.
    Teseted all C5707 Ok.
    ????

  66. Jonathon Says:

    Hey guys, I actually have a BenQ FP757 v2 that I rescued from the throw away heap at college. From what I’ve found, this monitor uses a similar power/inverter board as the Dell’s you are talking about. I was thinking about replacing the transistors, and then read the baccaps forum that suggests the problem could also be a transformer or capacitor. Since all three seem to be the culprit in different cases, is there an easy way to figure out which is the problem, or is trial and error the best route? Also, what do you guys use for soldering? I just have a standard solder gun with standard solder, but I would think silver solder and maybe a smaller solder gun would be better.

  67. ted Says:

    Thanks for this site. I just fixed my Dell 17″ monitor. Kinda waiting for it to go up in smoke. I did the best repair I could, but had a hard time seeing. Burnt a magnifing glass and a finger. Next repair I will have a self supporting magnifier. Thanks again.
    Ted.

  68. Ian Says:

    Hi
    Thanks for sharing your knowledge on the net, I now have two (15” 17”) working Dell monitors, both rescued from a skip
    Thanks again
    Ian

  69. Leo Says:

    Hello, i was having the same problem but when i took out the transistors they were all fine and had no sign of heat damage. So, i put them back into the unit and also resoldered all the pins on the wire wound components in the vicinity of the transistors. I put it all together and it worked. But, about 30 min later it went back to what it was doing. So, i took the transistors off and they were still good. So i put them on again and it worked for 30 min then dies. Turned it off. Then back on and it worked for 15 min then died. Now its just working for 3 or 4 seconds then shutting off like it did before i messed with it. Any idea what the problem might be?
    Thanks

  70. ratamaq Says:

    THANKS!!!!
    I bought one of these monitors off of craigs list for $30. Troubleshot it the first time and came across the bad caps forums. When I first read thru what was involved with repairing this I decided to just buy a new invertor board and replace that. The monitor worked for about 2 months and blew again. This time since I had a whole board of spare parts I decided to do it myself.

    Followed the steps, pluged it back in… WELLA!

  71. Peter Says:

    I have repaired other makes with the same problem but your instructions were very helpful. The case of these is very difficult to get apart. I used ZTX1051A which are E-line but can be made to fit and are cheap. They have higher breakdown voltage, lower Vce sat, but slightly less peak current at 10A. I wouldn’t put 2SC5707 back as they are discontinued and unreliable judging by the number of faulty dell screens.

  72. Jacob Says:

    Hi, TR,

    My Dell E173FP encountered the same problem that was power led stayed green(wouldn’t turn yellow when there was no signal suppplied) and the screen was black,I found a pair of c5707 and a 3A fuse damaged. I bought 2 pairs of MJE13007, 2 pieces of 0.22uf/250v capacitors and a 3A fuse.I changed them all.My screen works up to 6 hours and is still working. But there is a new problem encountered, the power led stayed in green, didn’t turn in yellow when there was no signal suppplied and when I turned the screen off power, the green power turned off with the screen remaining in white(back lights are on) which was supported to be black.

  73. DON"T FORGET Says:

    Don’t forget like http://www.badcaps.net/forum/showthread.php?t=1303&page=7&pp=20 says, you gotta replace the little fuse when you replace the transistors. They say it’s because when the transistors go, so does the fuse. Again, don’t make the mistake of replacing the transistors without replacing the fuse! Good Luck!

  74. Jeremy Says:

    I have a Dell E173FPc lcd monitor and when I plug it up and turn it on, the only thing it does is the light in the power button first shows yellow, then green, then it just turns off and starts all over again. I haven’t found anything on this model that has the same problem. If you have anything that would help me, I would love to hear it.

  75. Gary (California) Says:

    Syscom,
    I have appreciated your comments and have attemped to work similar magic on a prOview 19 inch, Model PL926Wbi. I have replaced two bloated caps and one that had an ESR about 3x the nominal value. This extended the light-up time marginally (if any). What appears to be the power switching elements for the back light are items in what appears to be in a TO-252 (or a D-PAK), it has ‘3055’ across the face with no other info. Now this is my dilemma, do I select a NPN epitaxial si transistor, an N-Channel enhansed mode FET, power MOSFET or some other device? I need guidance and was hoping you had some advice. Thank you.

  76. Jens Says:

    Dear All,

    if someone needs the 2SC5707, I can get it for 2€ / each.
    I will ship from Germany. Shipping costs must be added.
    Only give me a short note to jene72 at googlemail.com

    Regards,
    Jens

  77. Jordan Says:

    So i took my whole screen apart to check the same resistors as you said above in the tutorial and the board looks clean like brand new IDK if the resistors are bad yet but could there be a different problem because i know a bunch of other people had the same thing as me

  78. Roberto Says:

    What if the monitor stay totally white (bright white)

  79. Gaspare Says:

    Thanks guy! This article helped alot! The transistors were shot and I was able to find exact replacements. Im pretty good with soldering PC board components in electronics but I was not sure in the direction to go since alot of these parts are not testable unless you remove them from the board as you mentioned. Great article!

  80. Pecolt Says:

    Can saw me some In circuit bus BenQ FP-71G+ , what’s the element Q805.Thanк!!!

  81. Yoshi Says:

    I had two bad 2C5707 and fuse. so i replaced them and everything was good for a few days but today I saw the power button was flashing so I read your site again and it seem that people had the problem too. So i replace the other two 2C5707 and two FU9024 but now the monitor turns on for two seconds and the screen goes black.

    Can someone help. .driving me crazy !!

  82. Gareth Says:

    Many thanks, I now have 2 working Dell monitors :)

  83. jim Says:

    Great stuff
    Very useful advice in the main blog and loads more in the responses.
    We have a totally dead monitor that needs the kiss of life if it is to avoid the recycle bin. Now to get my hands dirty.

  84. David Says:

    Picked up mine at the dump and got it working by cutting the diode and trace feeding the bad inverter. I told myself there was a restful shading effect with only one backlight working. But after a few months the protection circuit decided to shut it off so I got here with google. I could find the bad transistors without desoldering, one was shorted and the other open. Replaced with two ancient TIP3055s from the parts bin, they are midsize so only had to make a cutout in the chassis for one of them.
    Thanks a bunch!

  85. brock Says:

    just did the repair and the green light stays on starts find than goes to black? turn it off and than on again and once again only stays on for a few seconds than goes black?

  86. bagbert Says:

    Just wanted to say a big thank you to the author and other posters for all the great info – I was a total novice at this type of thing, but managed to successfully fix my Dell e173 with the help of this page. Really appreciate the time you’ve taken to reply to most posts.

    There is one thing that I’d like to add – it was a very obvious mistake on my part (embarrassing!) but worth mentioning I think. In order for the fix to work, you need to make sure the transistors are inserted in the right orientation i.e. facing the correct way. You can see the correct orientation in the pictures above. Like I said, an obvious mistake but one that I made nevertheless. Doh!

  87. Kempis Says:

    Hi,
    I had the same problem as Tkniques above. I have changed twice the 2SC5707 and the monitor works for about a week and after that it goes dead again. The green power light is blinking. What can I do to make the repair permanent? Thanks,

  88. siebo Says:

    always look for bad solder joints in the inverter area (near the 4 yellow hight voltage transformers) . also resolder the 4 transformers.

    the transistors goes bad because bad solder joints. If you don`t do this, the transistors go defect again very soon

  89. matt Says:

    I have also replaced all 4 of the 2SC5707’s and the FU9024N’s … monitor worked for about a week or less and now when you power it on it just goes black after a second or 2. Is the transformer inside these monitors going bad?? Caps all look fine to me… so do the solder joints. Any help would be greatly appreciated, I have a TON of these monitors all experiencing the same symptoms.

  90. freddyzdead Says:

    The only thing wrong here is that the 3055 transistors will not do the job of the 5707s. The 3055 is a low-frequency audio transistor; the job requires a fast-switching, high-gain unit. The 3055 is neither of those. That is why they fail after a little while. There also may be further damage caused by heat. The circuit board is cheap consumer grade with thin copper laminate and will not tolerate overheating.

  91. Paul Says:

    Just wanted to say thx for help with my BenQ 767-12 LCD no back light. I changed the 5707’s but no change, so re flowed some solder joints, and jumped the 571 fuse with an automotive blade fuse. All good so far.

  92. Cletus Says:

    Gday, thx to this blog, my BenQ 767-12 is now running. I changed the 5707’s but the originals checked out ok and no change. I then jumped the fuse PF751 (looks like a diode) with an automotive blade fuse and resoldered the transformers and hot section and voila!

  93. John Klien Says:

    The link below shows the schematic for the LCD inverter.

    http://www.lcdinverter.co.uk/env056.htm

    I’m an electronics design design and has been designing circuits for 29 years. When I saw the schematic, I noticed that there is a design problem on that lcd inverter circuits. Look at that schematic and you will notice that each 2sc5707 has a 1k bias resistor. This is bad because during startup both transistors may turn on at the same time and the inverter would not oscillate causing the transistors to burn.

    The way it should have been designed is that only one bias resistor should be there, so during startup the transistor that has the bias resistor will come on first and the transistor not connected to the resistor will be isolated from the bias resistor by the inductance of the transformer thereby guaranteeing only one transistor conducting at the start.

    So to fix the design, remove resistors R748 and R768. Replace R749 and R769 with 750 ohms.

    Make sure you fixed the board first before doing the design modification.
    This design fix is to prevent the recurrence of the transistors burning up again.

    • Ed Says:

      John is right, I had replace the 4 transistors and 3 amp fuse only to have it turn on for a split second. After removing R748 andR768, and replacing R749 and R769 with 750 ohm resisters it powered on perfectly. Thanks John!!

  94. Ubong Says:

    Hi to all,
    I must confess to the good job you gays are doing in here. I had the problem stated in Dell E173FPc. After reading the procedures i quickly carried out a test on the C5706 at the inverter circuit. It showed that two of the transistors were bad. The real problem came when i could not find C5706 in the electronic shops here in Lagos, Nigeria. I did not want to use 3055 because of…. I was introduced to C3074 whose characteristics were a bit similar to C5706. Four of C5706 were replaced with C3074. Believe me, it worked!!

    Thanks gays

  95. MissingFrame Says:

    It’s very nice that you have this page, opening the case is tricky. Even though it’s been mentioned elsewhere, I think something at the top should mention a warning that many of the fixes simply aren’t permanent. I got about a month of use before it died again and for a monitor that you can replace for less than $100 USD it’s not worth replacing transistors once a month.

    I think it’s pretty obvious these things weren’t engineered correctly in the first place and not worth fixing without some redesign. Peter mentions ZTX1051A which is a good find but personally I’m not spending any more time and money so mine is hitting the landfill.

  96. Eric Says:

    This fix also worked for my Benq FP91G+. That monitor would turn on for a fraction of a second before turning itself off. Based on the information on this page I removed the 4 transistors. One of the 4 transisters was open. I replaced all 4 with C5707 transistors.
    It worked.

  97. fasalurahman Says:

    first time tern-one the monitor light is ok . after two seconds will automatically
    tern offing monitor light ?????

  98. Bonnie Says:

    Thank you for the instructions! It’s working great!

  99. ShicheDer Says:

    Fantastic website Hope to come back.

  100. Jerry Says:

    Great instructions. Have never repaired a computer monitor and after one small glitch (our fault), we were able to complete the job.

    Our pcb looked a little different than the schematic and we took a little time making sure we were replacing the correct parts.

    Also, we used Radio Shack TIP3055 transistors (and had to modify the casing so that the heat sinks on these larger transistors did not touch the casing).

    (total cost $11)

    THANK YOU VERY MUCH

  101. Barry Arnold Says:

    I hope this is of use , thank you for the time and trouble

    http://uk.farnell.com/jsp/displayProduct.jsp?sku=1554597&CMP=KNC-GUK-FUK-GEN-SKU-OTH&s_kwcid=2sc5707|3425185959

  102. Don Says:

    Guys, I just ordered 10 of the Sanyo 2SC5707
    Transistors from thecapking.com. The total bill came to $8.00. No tax and no shipping.

  103. Russell Says:

    Thanks for all this information. I am viewing this on my newly fixed dual dell 17″ monitors!!!

  104. frances Says:

    Not sure if this blog is still active, given the last entry was seven months ago, but I must say it is contains the best, most sensible discussions and tips for repairng flat panels anywhere on the web. I was drawn here as I have simialr issues with one of my Benq FP71E+ monitors. It occasionally goes black, preceeded by a greying of the upper part of the screen. Rapid switching on and off and the occasional hard thump on the desk restores it temporarily, as does disassembling and reassembling it, but it always reverts to bad habits eventually. In my experience, flat panels respond to a good thump more than any other electronic device. Why, I do not know, but with all the dinky-toy connectors inside them, I’m not surprised. I have 15″ Dell that occasionallywhites-out (full backlight but no signal). A very hard, heel-of-the-hand thump (so hard I expect the glass to break) on the right hand bezel fixes it for surprisingly long (weeks) periods. Anyway, I’m getting around to resoldering everything in sight to see it that changes anything (for the better, hopefully.) Meantime, I can’t stress enought the theraputic and remedial benefits of a satisfying thump.

  105. Sasa Says:

    Thank you! Changed one 5707 and a pf751 fuse (patched with a piece of wire) and I am typing on it right now!

  106. Mike Nolley Says:

    Fixed a broken Dell LCD that I got at Goodwill for $10, in its broken state. Got the transistors from “CapKing” and they work fine, *and* I have a few left over! Thanks a million!

    –Mike

  107. Billy D. Says:

    I have a Dell E173fpb lcd that goes blank after about 5 seconds. The power light does NOT blink. When the display goes blank, I can still see the test pattern on the screen using a flashlight.

    My question is, is this the backlight or the inverter? How do I test for one or the other?

  108. Billy Says:

    I have a blank screen on a Dell E173fpb lcd but NO blinking power button. The display, when just hooked up to power, comes on for about 5 seconds with the test pattern then goes black. If I shine a light on the screen, I can still see the test pattern.

    Is this a backlight problem or an inverter problem? Is there a way to check one or the other so I can be sure what I need to replace? If it’s the inverter, is it just a matter of replacing the 2SC5707 transistors? I’ve checked fuse PF751 and it’s ok. If I do replace it what part number do I get and where?

    I know that’s a lot of questions, but this place seems pretty helpful.

  109. Michael Says:

    Although not technically the same as the monitor mentioned here, I have a Benq FP71E+, was suffering the LCD backlight switching off after a few seconds…
    Although the layout of the transistors is different, I replaced the 4x C5707 with 4x MJE3055.
    I did not have the space problems inside of the metal shield as is the case with the Dell monitor, I have plenty of room above the transistors!

    Thanks for the a wonderful page of help!

  110. david Says:

    I needed this! Thanks!

  111. Brian Says:

    Hi there. Good blog. I have an LM722 AOC monitor that has a flashing green power led. I can hear a faint ticking like a relay latching whenever the led illuminates. Have ripped it apart (as you do) to check it out. No sign of any bad caps, or overheating, or anything of that ilk. Can’t find a relay anywhere, so not sure what the ticking sound is…
    I have tried thumping as frances suggested, and it was very satisfying, but alas did not improve things. Interestingly the Video card (7600GT) that this was attached to failed at the same time. Not sure if the monitor took out the video card, or vice versa, or whether it was just an unlucky coincidence. I have since tried the 7600GT in another PC and it is producing weird distorted images so is clearly buggered. I have never heard of a video card taking out a monitor – have you?
    Any ideas where I could look to fix the monitor?

  112. Arvind Says:

    I had the same problem with my Dell monitor and replaced the transisitors and now it works well. Aa a result at South Island Components, Christchurch – we now stock the 2SC5707 transistor. It is more expensive than the MJE3055 but save a lot of time and trouble.

    regards

    arvind

  113. Kevin G Says:

    Great Blog! I am hoping to use this to help me out.

    Just today my Dell E228WFP started this nonsense – backlight would turn off, but monitor still on and image could barely be viewed.

    Of course my warranty expired on August 11.

    I have a few questions for anyone with some experience:

    1) I am in the US – what transistors should I use? I am reading that some used may burn up or catch fire. Don’t want to mess with that. I want to do it once, the right way.

    2) I’ll make sure the solder joints on the transformer(s) are good. Is there a need to replace the transformers (i.e., will they fail soon too), or will repairing the joint on the transformer and using better transistors give a long life?

    3) Can the entire board be replaced? If so, can you point me to a source?

    I am studying for my CPA exam, and had to revert back to a cheap, blurry, 17″ CRT. It really shows me how spoiled I’ve become with the 22″ LCD! I have a headache from completing practice exams all day on this old piece of junk!

    Thanks again!

  114. nacho Says:

    Hi there:
    I have been trying to fix my 19″ kds lcd monitor for the entire summer. the symptoms : The screen went black after 3-4 secs after turning on the pc. I did some online research I follow some advice about putting a flash light in front of the screen and effectively in the back of the screen I could see everything. I follow the tips and changed the 2 electrolitic capacitors in the inverter board that were burned. I was confident this was going to solve the problem. Well. It solved the problem of the black screen for about 1 minute and then the screen went black again. I read the instructions on this website and check out that one of the two pairs are of the bubls are burned. this might solve the problem. the question is: how can i know of the technical specifications ( voltage, amps,etc)
    on the burned bulb in order to buy a new one? thnks

  115. ema Says:

    ————————

    Hi.
    My Benq 767-12 monitor has the same problem: every 10 minutes it turns off for one second then it works again. I think that when it is hot in my room, the monitor has this behavior often.

    I open the monitor, removed the transistor and measured them. All show the same characteristics and seem to be ok (2.2KOhm between base and emitter/collector; and almost infinite resistance the other way).

    The capacitors are also ok. None is inflated or leaking.
    I have also re-soldered those 4 high-voltage transformers.

    But the monitor still shows the problem.
    What else to check? Maybe something that is related to heat.

    —————————–

  116. Dr FixIt Says:

    Anyone with this problem, you can get the original replacement parts here:

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=220486136668

    I used this kit and have fixed 3 monitors.

  117. freddyzdead Says:

    Hi again, I’d just like to warn people again that the 3055 transistors most definitely will not do the job. The 2SC5707 that is used originally is a very fast switching transistor with much higher gain (hfe) than most transistors have. If you put in 3055s, they will get hot and self-destruct, maybe taking other components out with them. Here is something useful I discovered:
    If you have some old Pentium motherboards around, you will find near the processor socket some power components for generating the CPU core voltage, usually around 1.5 volts. Some are FETs, some are bipolar, the bipolar ones are what I used to replace the 5707s and it works beautifully, no heat at all. The Benq monitor I did this way is nearly identical to this Dell one. Well, ok, it’s made for Dell by Benq; it’s been running flawlessly for months and months. This inverter is a bad design by Benq and this fault is very common. So if you can’t/don’t want to hunt down the 5707s and you have a pile of old motherboards, then you should try this.
    I don’t know where all this bad caps stuff comes from; somebody found bad bypass capacitors causing trouble on a motherboard and now blames them for everything! I’ve been messing around with this kind of stuff for 40+ years and hardly ever see bad caps.

  118. James Hartley Says:

    Do you have anything in print on trublesshooting flat-panel TVs
    power supplies ?

    Hartley-TV-Repair
    109 Cedar St.
    Richwood,Tx. 77531
    Email: jhartley42@yahoo.com

  119. peter Says:

    am looking for c5706 or its alternative for my dell lcd monitor, it displays that the monitor its working properly but after connecting to the cpu the display is inderneath after openning the monitor I realised that transistor C5706 was not working after replacing the other pair failed now help me if you have any suggestions. thank you.

  120. Paul Says:

    Hi there,

    That is a great guide you have made. I wonderif you could advise me on a similar problem?

    I have a dell laptop with wuxga screen and the ccfl tube stopped working. I replaced the inverter with a new one but still nothing so I stripped out the ccfl tube.

    I plugged the inverter and ccfl tube back in, independent from the lcd screen so I could see what was going on and I found that the tube lights up for just a split second when I power on the laptop then nothing. This will happen every time the laptop is restarted, just a brief flash from the tube which is around 5 years old.

    I am currently using a secong desk standing lcd through a vga cable and that works perfectly so I guess my graphics card is fine.

    Can you comment on what you think the problem may be?

  121. savageinjun Says:

    I am duly impressed with the instructions given here. i have been to a couple of other pages before i came to this one and all of the others were about complaining and about how this will kill me from electrocution. lol…i’m sure it would if i decided to pull apart all the transistors,diodes,and what-have-you on the PCB and if it was still on. yeah right Einstein… anyways I have found another site that sells the C5707 that is needed for the fix… http://www.afforthecc.com/cgi/search.pl?S=C5707&C=36330
    there are a variety of packages made up. rangeing in price from a dollar (singles) to over a hundred bucks (quantity) hope this helps and thanks for the information… you are a tech god.

  122. savageinjun Says:

    *EDIT* Also forgot to mention..the Board is stamped with the Benq logo…i have the Dell E172FPb model. lol.

  123. Gamaliel Says:

    Hi, I´m having some problems with a flat monitor HANNS-G model HC194, it was working well til start to go off and on then it was off forever. When I put on the ligh is lime and flashing but the monitor doesn show nothing on screen. I need some help on it Please.

  124. Nate Says:

    Just finished replacing the four transistors, and the Dell is up and running again! Thank you for the easy to follow instructions. This was my fist circuit board fix, and I had no experience going-in. Thanks again for saving me the cost of a new monitor.

  125. Ed Pagan Says:

    I wonder if you can help me, i have a dell 19″ se198wfp that doesn’t power up, I want to buy components for it and dell won’t sell the parts to me. First it powered up but then it started to flicker. I opened it up again looked at the power invertor board, I don’t see any burn , also the ab logic board. can you help??? thank Eddie P.S I can’t find a company that carries this board, and I rather fix it my self than sending it to get repaired

  126. HD LCD TV Says:

    Hello you have a great blog here! I’m definitely going to bookmark you! Thank you for your info.

  127. freddyzdead Says:

    @John Klien No that is wrong; no two transistors have exactly same gain, so one always turns on first. No way would it fail to oscillate for that reason. Are you sure you’re a “Design Design”?

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