AOC LM722 LCD repairs

100_1343.jpgOne of my real bad habbits is picking up faulty junk off trademe in hopes of me repairing them and making use of them, I just cant stand how people end up throwing away good stuff which only costs $1 to fix (no really, only $1 or even less!!!). Luckly for me, someone elses loss is my gain and also luckly for me, Ive had some good luck in this area, in this case, picking up this faulty AOC LCD Monitor for the cheap cheap price of only $45, Ofcourse, it did have this minor problem of actually being faulty.

The auction described the monitor as  “*****POWER PROBLEM WITH MONITOR, IT DOES NOT STAY ON! COULD BE AN EASY FIX FOR SOMEONE WHO KNOWS WHAT THEY ARE DOING.************”
After having it arrived at work in its original packaging (really must stress the packaging, once the screens cracked, or have dead spots, nothing left to do but dump the poor thing), I pluged it in and sure enough, the monitor would turn on for about 2 seconds and then nothing.

Suspecting the backlight as bing the issue, I grabbed a tourch and tried to see if there was a dark faint image on the screen, no luck, the monitor had actually gone on standby mode (indicated by the orange led). Further diognostics required taking the unit apart…. heres some quick notes on how to do this (without putting too much stress on the plastic and the actual lcd).
You will need only 2 screw drivers (one philips for the screws and one flat head, for best results and to avoid damaging the plastic, go for the widest flathead you can find) and a small spanner.

Ok, some pictures on removing the plastic casing.

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The insides (click for high res)

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The problem!

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A visual inspection quickly showed the croperit, the pluge of the bad capactors strikes again.
After a quick replacement of the cap, I quickly put the sheild back on and gave it a quick wheirl. Fixed!!!
Reassembled the casing and left the lcd running over night with a  screensaver. By morning, still running and has

been for over 3 weeks now.

Net Result? Dual Monitors!!!

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So, whos up for a cheap LCD? 🙂

Brand: AOC
Product name: LM722
Model Number: TFT1780ps+

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18 Responses to “AOC LM722 LCD repairs”

  1. Angel Says:

    Hi there!

    First, sorry for my English, it is not my native language. Second, good job!

    Third ;), I have the same problem with the same kind of LCD, an AOC LM727: Stay on for a few seconds, then screen goes black. If I did carefully look, I was able to see the image, so I suppose it was a problem with the backlight.

    I have already openned it (I didn’t know your page and it was a pain in the ass, now it is funny to see pictures of the same parts that I have seen). How did you know that capacitor was the bad one? I thought the cause was the red things cover with plastic (I don’t know the name).

    I was looking for a replacement of the entire part, but I have not found any yet. Now I am going to replace the same capacitor (wish me luck!). Any suggestion?

  2. syscon Says:

    Hi there, the thing I look for when looking for bad parts is pretty much anything thats out of the norm. In this case it was pretty obvious, The capactor had a bent top (looks like its under presure rather then a flat top as it should). Pretty much the design of these types of capactors mean that when the start to fail, a common result is that they build up with gas (i think this is relating to heat) and eventually the vents at the top open up.

    The red plastic things are also capactors but of a different type. My udnerstanding is they dont die as easily as the cound metal types, however I have seen them die in the past.

    I would start by looking at the larger (420uf or greater) caps and see if they look stressed (hot water cilinder looking like its going to pop). There are ways of testing which is alot better then visual (testing their ESR) but that is normally a long process that requires removing the cap from the board to test and if you are going to test alot then that becomes along process.

    If no luck then I would start looking at the transistors and diodes around the inverter area, esp the transistors doing the push/pull for teh transformers around the inverters (I’ve had them die, documented on the dell lcd posting (https://syscon.wordpress.com/2007/07/13/dell-dell-e172fpb-lcd-backlight-repair/)

  3. syscon Says:

    Quick note: PLEASE PLEASE be careful when playing with the monitor if its pluged into the wall…. Lots of bad stuff could happen and could cost your life. I only make changes when its not pluged in, I then put the case back on (to avoid acidential shorts against anything i have around like a screw driver or something) before plugging in and testing the changes…
    You dont have to reassemble the whole lcd but screwing the boards in place is a must and laying teh lcd panel in its correct position is prob a good idea too (so you can avoid putting the front frame on to make life easier)

  4. Angel Says:

    Do not worry Syscon! and thanks a lot!!!

    I have replaced the capacitors but I think they were fine. Anyway, I think I have solved (althought partially, I am sure) the problem. Since the circuit is symmetric and only a half was malfunctioning (the symmptoms are exactly the same that for your Dell LCD, one of the backlights does not turn on and the other turn off after a while, to protect itselft I suppose), I tried to interchange components from one half to the other. By chance, I tried to replace the diodes that you mentioned, but I was not be able to do that (I am very bad desoldering, and they became too hot), and a pair of coils with the same luck. After a while I dessisted and put all togheter thinking on buying a new complete inverter or even a new monitor. But then, it worked!

    I don’t know why (was something unplug or almost?, could the heat help in some way the dioides? sometimes, after let it plugged both backlights turned on and it worked for a long time) but I decided don’t touch anything! 😀

    During this weekend it have been working well, except for some backlight blinks (from very long time to time) that worried me a bit. I think I will eventually replace the diodes (after reading your post for the Dell monitor, I think they are the cause), but for now it is OK.

    Thank you very very much for your help! and keep doing do good job with your blog!

  5. Myke Says:

    Hy guys, I have an AOC 727 lcd, with the same simptoms like yours, suddenly just started blinking the upper light, and then it went of, and after a feew seconds the LCD started acting like it does’n have signal (a black screen) Afert mesuring some capacitors, I changed 5 of the 16v 470micro capacitors, and 2 of 16v 1000micro capacitors. In the end the LCD is working without any problem… 🙂 I think that those bad capacitors are the source of all the defects that makes tha AOC 7xx series make stupid things.

  6. syscon Says:

    Hey Myke, Its great to see someone else who managed to get anotehr AOC working 🙂

  7. N overend Says:

    Hi I’v got AOC 176S & it runs the same boards but you plug it in turn it on & nothing no light just a total lack of power the caps are fine is there a fuse
    on theses boards if so witch one is it or would it be somthing elsecould someone help a stuck kiwi cheers

  8. flayzer Says:

    i have same problem with the 727… works fine for 5 mins then the screen dims slightly then turns off but the power light is green, turning it on and off brings it back to life or letting the pc go to standby then waking it up.
    I have replaced all the 470 and 1000uf caps with 25v ones and still is the same, resoldered all joints too.
    It just seems such a shame to chuck it away

  9. Matt Falcon Says:

    Haha, another AOC problem. Google guided me to this one.

    I had a much, much, much more complicated solution to a problem with a “junker” LM929. The power board looked very, very similar to the one in your picture, except the transformer was closer to the center of the board and had a connector for the audio (yes, on the power board) that plugged straight into the audio amp (?) board off to the side. Still 4 backlight connectors.

    My problem was a widespread failure of the high-side MOSFET, I believe. It blew the fuse and when I tried shorting the fuse (bad idea, I now know), it blew a trace off the board in a puff of smoke. I later found that the MOSFET chip was internally shorted, 0 ohms on all 3 contacts. I ordered a replacement chip and while it stopped the explosion, it didn’t fix it, and later tinkering ended up totally obliterating the new chip (probably by locking it “high” by accident and overloading the sh*t out of it).

    My long-way solution actually involved a dirt cheap 12v/”3a” power supply off eBay – $10 shipped to be exact. The first thing I did was crack the case open and found the cheap components inside. The low-side rectifier (I think is its purpose…?) got hotter than hell and would nowheres near allow it to sustain the 3+amp draw that monitor needed. I hacked it up, removed the single chip the PSU came with, and wired its pins to the two chips that were on the original AOC power board (and breaking contacts with them from the rest of the original board). After doing that and replacing the filter capacitors with higher quality/capacity ones, I ended up with an ice cool replacement power supply (those two chips more than quartered the heat output) that runs this monitor like a champ now. I wired its AC input to the original power socket (through the fuse contact and one of the filtering-stage “coil” thingies), and the DC output to one of the empty capacitor pads near the power plug. It also requires 5 volts, but there’s an auxillary regulator that converts the 12v input to 5v (feeding it “backwards” seems to cause no problem there). I Velcro’d the new power brick to an empty spot in the case and sealed it up.

    New monitor! 😀

    ‘Cept for one problem, the one I was Googling for. Everything works perfect on this monitor except for when I put my computer into Standby (probably even if I shut it down, which I never do). It then says “Cable not connected” and stays on, bouncing that damn “Cable not connected” message around the screen. If I leave the computer on and let it turn the screen off, it turns off. I have to hit the power button on the monitor to turn it off whenever I Standby my computer. I think it’s an issue with my video card + monitor combination… but I dunno. Sure is an annoyance… =(

  10. Max Says:

    Hi, I had the same problem with a AOC LM727 monitor, the logo showed then a second
    of windows then it went blank, the menu would display very faintly, solding the coils
    fix the problem, this site might help:

    http://www.starwars.myzen.co.uk/AOC-LM727/

  11. Mark Chamberlain Says:

    I had the same problem on an LM729. I found exactly the same capacitor failure as you show in your pictures. Replaced it and all is working.
    The hardest part is taking off the cover. Thank you for the photo’s they helped a lot.

  12. Emma Says:

    Hi, I followed the instructions on replacing the capacitors, I put it all back together, but the screen is coming up white – no display… It was just turning itself off previously, so I am half way there, Just wondered if you had any ideas as to why the display is just white?

    Thanks in advance.

    • syscon Says:

      Sorry for late reply, if you still having this issue, I would check to see that all cables are in correctly (esp the data connection between the panel and the booard which is usually a ribbon cabale of sorts). The plug can oftern come loose or bent pins etc which causes the same desceribed symptoms

  13. Mikes Says:

    I managed to give myself a little shock off of one of these things…
    I have the same symptoms (display goes black after 10 seconds, it’s the backlight going off as you can faintly see the display still)

    I am somewhat of a novice, but all the caps look fine, the big black “battery” looking thing (is it a capacitor?) has leaked all over the board.

    I’ve uploaded an image here:

    reckon it’s worth just ebaying a new power board?

    Thanks for the information on opening the thing, man, I’ve done easier jigsaw puzzles than opening that PoS

    • Sivera Says:

      The stuff you see underneath the Capacitor is glue, to keep the big and heavy cap in place, to ensure that it does not shake loose.

  14. Clive Says:

    Hi, I’ve got a couple of AOC LM-700’s, one of which is fine. The other powers up and there is always a screen display, but the screen presented is awful. Starting from cold, it can be ok for a few minutes, but it soon does some or all of the following

    a) all characters appear thin and out of focus. The focus control has no apparant impact.
    b) when the brightness is reduced to zero and contrast is around 30, its ok for a while, with the characters blacking up and being in focus.)
    c) the colours seem to invert or lose a colour (its very confusing)
    d) if the brightness is increased past 30, it seems to get a little lighter, then around 60, screen rapidly goes all white and you can’t see anything.
    e) the backlight starts blinking, with brightness varying with each blink.

    I suspect its a heat-related problem, can you point me in the direction of which one please????

  15. George Says:

    Thanks heaps, Syscon.

    I’ve been running dual monitors for 6 yrs: ViewSonic VP191s and AOC LM722. Had no trouble whatsoever until a few weeks ago, when the AOC started playing up – going black after a while. It would come good when I switched it off, but the day arrived when that no longer worked, and it stayed on for only a few seconds. Then not at all.

    I tried Googling a few different combinations, but with little success. Some said the graphics card was the problem, but I tested that and knew it was ok. Then I tested the AOC in another computer. Aha!

    So I Googled again and found your blog containing the exact description of my problem, plus clear instructions on how to dismantle and fix the thing, AND photos with little arrows – wow! I’m no electronics expert, but I know how to use a soldering iron on circuit boards, so I figured I had little to lose. And if I couldn’t fix it, that would be just the reason I needed to buy a fancy new monitor.

    After dismantling the monitor, I found the dead capacitor. It was the same one as yours, and looked the same, with the top slightly bulging out. Unsoldered it from the circuit board, and marked which way it was orientated, just in case that was important. (I had learned that from fixing my various cars for over 25 years). Went to my local electronics store in Sydney with the dead capacitor and asked for 2 new ones (I thought I should get a spare, just in case…). Cost me 90cents each. I asked if they had polarity and was told “No”.

    Went home, soldered one of the new caps in, put the monitor back together (well, the most important bits, anyway), connected it and switched it on. A slight flicker, then nothing. Turned it off, checked the connections and tried again. Heard a soft, strange sound, then saw a bit of smoke wafting out from the back! Yipes! Turned it off quick-smart and unplugged it.

    Dismantled it again and saw that the same cap had blown. Unsoldered it, looked carefully at the circuit board and saw a little + sign on it, near one of the holes where the pins had gone thru. Checked the original capacitor and saw printed on it what I figured must be a – sign in line with one of the pins. And my mark confirmed that the orientation was related to polarity. So I figured that the salesman got it wrong. But shouldn’t he have known better? I mean, it wasn’t a packet of Corn Flakes he was selling.

    I had no idea what damage I had done to the circuitry by apparently reversing the polarity of the new cap, but figured I had nothing to lose by trying with the spare one, and if it still didn’t work, I’m off to buy that new monitor after all.

    Anyway, I soldered in the spare cap, taking care to get the polarity right, put the monitor back together, connected it all up, switched it on and stood back. It was with surprise, pleasure and a slight disappointment that the screen came to life again.

    So thanks, Syscon, for your fantastic help. But now I have to think of another justification for getting a fancy new monitor.

  16. Neoss Says:

    LM-729=lm727 http://www.eserviceinfo.com/equipment_mfg/AOC_3.html http://zorg.tripod.com/ C201
    150uF/25V C223
    150uF/25V Q202
    DTA144WKA Q201
    DTC144WKA
    works fine for 5 mins then the screen dims slightly then turns off but the power light is green, turning it on and off brings it back to life or letting the pc go to standby then waking it up.

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