AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

[WackyWeasel]

I have a AOC E2460PDA LED-backlight Monitor (built 2012) which is giving me troubles. I am not an EE, however am competent enough to solder an replace caps (as I did with my trusty HANNS.G HG281d). Any pointers would be appreciated!

The device

• Specs: AOC E2460PDA Specs
• Service Manual: AOC E2460PDA Service Manual

Symptoms
Monitor goes black after a while; the power indicator LED is going off as well. If I press the power button, nothing happens (everything stays black).

But in this state, the monitor is still recognized by the OS as if it was working.
If I replug in the mains cable again, the picture is coming back without any problems, until after usually ~20 minutes, the monitor starts going dark again.

Picturewise, there are no troubles at all; if the monitor IS showing a picture, all's very crisp and steady (both from DVI & VGA)

Pictures
I took pictures of the power supply (PN 715g5361), I did not see any bulged caps (most of them are Elite branded). After turning the power off, the voltage on the big cap decreased rather quickly, I don't know if that's okay.

[momaka]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

With the monitor appearing to die only after a while (with the power ON LED turning off as well), I'd be more inclined to think there are bad caps on your video/logic board. Could you post some pictures of that? The video/logic board is the one that has all the video inputs.

That said, the next thing on the list would of course be the Elite caps... though I doubt they are causing the issue you are currently describing.

[WackyWeasel]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

Note: the link in the first post for the service manual is not 100% correct.
Correct Link

Okay, I took out the logic board and spotted 3 electrolytic caps, all of them "JH" branded and without any visual defects.

All three are rated 100uF, 16V 105°C, as stated in the service manual

I know it's in circuit, however I did some measurements with one these cheap Ebay component tester to check for capacity and ESR (after shorting the leads before measuring).
C705: ESR=0.88 Ohm, Vloss=7.2%, Cap:116uF
C702: ESR=24Ohm Vloss=17% 127uF
C430: was not recognized as part (maybe the culprit?)

There is another small PCB for the switches and another one fixed to the screen itself.

[piernov]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

C430 might not be recognized due to in-circuit measurement, but it might be dead too.
However, C702 has a very high ESR so make sure you're making good contact. If the ESR is still high, it's bad. You should replace the 3 caps.

[momaka]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

C430 might not be recognized due to in-circuit measurement, but it might be dead too.
However, C702 has a very high ESR so make sure you're making good contact. If the ESR is still high, it's bad. You should replace the 3 caps.

Indeed.

Hard to say if the problem is 100% caused by C702 (and/or C430 for that matter), so you should remove these caps and test them out of circuit. If C702 really has more than 2-3 Ohms ESR, it's probably best to replace it, along with the other two caps.

That said, if you are buying caps, you might as well do the whole power supply board too (minus the big primary input cap, of course). That way, we can eliminate caps as the possible cause of your monitor's problems.

The only other thing I can think of is if there is a bad solder joint somewhere on the power supply board. But based on the pictures you provided (which are of excellent quality, by the way - big THANK YOU for that, as it makes troubleshooting much easier ), all of the solder joints look nice and shiny.

That said, I have seen this one issue on a Dell monitor once, where they used analog voltage readings to the front panel buttons. As the monitor warmed up, though, and due to its age, the IC would read the voltages wrong and so the menu would pop-up by itself. I found I can remedy the issue by adjusting the resistive dividers for each button, thus compensating for when the IC is hot. But I strongly doubt that's the issue here with your monitor.

[WackyWeasel]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

After de-soldering the three caps from the logic board (a PITA as always...), I measured them out nof circuit now:

C705: ESR=0.67 Ohm, Vloss=2.1%, Cap:101.4uF
C702: ESR=0.64Ohm Vloss=2% 104.3uF
C430: ESR=0.7Ohm Vloss=2.6% 100.6uF
(again, all three are rated 100uF, 16V 105°C)

Measurements are to be taken with a grain of salt, since I didn't use professional equipment, just a LCR-T4 component tester.

However, I think these caps are not to blame?

[momaka]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

However, I think these caps are not to blame?

Yup, they look alright on the ESR meter. For small caps like that, typically up to 3-4 Ohms ESR is not considered bad.

That said, let's try the following approach: try measuring the output voltages going from the PSU board to the logic board when the monitor is working and when it isn't. That should be the 5V rail on pins 6 and 7 on connector CN902.

This should help us narrow it down if the PSU is shutting down due to a fault or if there is something else wrong, perhaps with the logic board. I see only a single transformer on your PSU board (minus the inverters), so that means the PSU is always-ON, regardless of the state of the monitor. Thus, the 5V rail on pin 6 and 7 on CN902 should never go out.

If the 5V rail indeed never goes out, then try measuring the voltage on regulator U702 input and output pins when the problem occurs and also when the monitor is working fine.

Alternatively, you can try tacking the issue by removing the caps on the PSU board and see if there are any bad ones there.
...
Or just order new caps and replace everything if you think that is easier, so that we can rule out bad caps as the cause of the issue.

[WackyWeasel]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

Sorry for the long time since my last post.

I desoldered all capacitors for both the logic board and the power board and measured their values:

Logic board 715G5270M

CAP   MEASURED*        SHOULD BE
C430  101.4μF 0.67Ω 2.1%   100μF 16V
C702  104.3μF 0.64Ω 2%    100μF 16V
C705  100.6μF 0.7Ω 2.6%    100μF 16V

Note: MEASURED format: Capacity InternalResistance VoltageLoss

Power board 715G5361P

CAP   MEASURED        SHOULD BE
C601  105μF - 0.43Ω - 1.1%  100μF 16V
C613  105.9μF - 0.39Ω - 1.4% 100μF 16V
C801  223.5μF - 0.26Ω - 0.6% 220μF 35V
C809  30.89μF - 0.29Ω - 0.5% 33μF 100V
C913  45.3μF - 0.5Ω - 0.8%  47μF 50V
C918  911μF - 0.1Ω - 0.6%   1000μF 25V
C920  770μF - 0.09Ω - 2.0%  680μF 10V
C921  778μF - 0.09Ω - 1.7%  680μF 10V
C922  332μF - 0.26Ω - 0.9%  330μF 25V
C933  942μF - 0.11Ω - 0.8%  1000μF 25V
C934  333μF - 0.26Ω - 0.4%  330μF 25V

Although none of the values were too far off, I ordered Panasonic FR series caps to replace them all. With one exception however: for C809 I used a "SSL" branded capacitor rated for only 85°C, since the store didn't have a FR series in stock with these specs. I'm not sure if that's alright?

Unfortunately, the solder pads came off for C702 and C933 (I used some bodge wire, C933 is in parallel with C918 anyway).

After powering the monitor on, there was quite a lot of green noise in dark areas (see gif), but after 3 minutes or so, the picture became stable. I am not sure what was the reason, perhaps because I cleaned the board with Isopropyl and water?

The screen is running for an hour now without any issues. Recapping apparently solved the problem it seems for now - if there are problems again, I'll keep you posted

[momaka]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

Although none of the values were too far off, I ordered Panasonic FR series caps to replace them all. With one exception however: for C809 I used a "SSL" branded capacitor rated for only 85°C, since the store didn't have a FR series in stock with these specs. I'm not sure if that's alright?

That "SSL" capacitor is actually Samsung SSL series - very old caps. I'm surprised it didn't pop, as that is a NOS cap that probably sat in storage for over 20 years. Also, it's only a general purpose cap and only rated for 85C, so it may not last very long in the monitor. I definitely suggest to keep the original cap, just in case this one doesn't last too long. I'm not sure what C809's function is, but if it's just filtering for an output rail, I would replace it with whatever is the next closest higher capacitance. And if the voltage on it is much lower, I would use a lower voltage cap too. That way, you would have more choices rather than looking for an odd-ball value.

Just keep this in mind: manufacturers don't always use the "most optimal" parts during assembly. A lot of times, they just use whatever is the cheapest at the time that is closest to what they need. So you do have some "wiggle room" to play with the capacitor's capacitance and voltage rating, usually. The only cap I would not mess with (as in, keep the same capacitance and voltage) is the startup cap. For your monitor, that appears to be C913.

Unfortunately, the solder pads came off for C702 and C933 (I used some bodge wire, C933 is in parallel with C918 anyway).

Yeah, that's not a very good way to do it. The long wire increases the effective ESR of the cap and also puts more noise in the power supply.

You can just scrape away the solder mask next to the lifted pad instead and solder the lead to that. A small flat heat screwdriver works well for scraping away solder mask. Just make sure to scrape down to bare copper. Then heat with you iron and apply solder. Once there is enough solder, just bridge it over to the cap lead.

After powering the monitor on, there was quite a lot of green noise in dark areas (see gif), but after 3 minutes or so, the picture became stable. I am not sure what was the reason, perhaps because I cleaned the board with Isopropyl and water?

Nah, the Isopropyl/water cleaning wouldn't have anything to do with that.

Does the monitor do this every time it is cold? If yes, you may have excess ripple/noise from the PSU. In which case, my guess is that it could be either the Samsung SSL cap or perhaps the solder wire bodge job.

Otherwise everything else looks good. Congrats on the repair.

[WackyWeasel]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

Thanks for all your valuable input!

On C809 33μF 100V

That "SSL" capacitor is actually Samsung SSL series - very old caps. I'm surprised it didn't pop, as that is a NOS cap that probably sat in storage for over 20 years.

Interesting, since the store is actually one of germany's bigger electronic stores (Reichelt, link to the article page; the picture shows a Samsung cap, the datasheet is for Yageo - I guess they sell "whatever" for general purpose caps).

I'm not sure what C809's function is, but if it's just filtering for an output rail, I would replace it with whatever is the next closest higher capacitance.

I'm not an EE, but the schematic says it's part of the "LED drive" (for backlight control?). I've linked the schematic as attachment.
I still have the original capacitor around, I wonder if it is better to keep the new one or to put in the original one.

On using the bodge wire:

Yeah, that's not a very good way to do it. The long wire increases the effective ESR of the cap and also puts more noise in the power supply.

I'm quite confident that I made contact with the PCB as well, so the bodge wire is there as an addendum - it shouldn't hurt I guess?

On the noise issue
I could not reproduce the noise after the first time I plugged it in - perhaps the plug didn't make proper contact. The monitor has been running without issues yet for some hours (also after cold starts).

[momaka]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

On C809 33μF 100V

I'm not an EE, but the schematic says it's part of the "LED drive" (for backlight control?). I've linked the schematic as attachment.
I still have the original capacitor around, I wonder if it is better to keep the new one or to put in the original one.

I guess it doesn't matter too much, as long as the capacitor is working and doesn't go high-ESR or open-circuit. Looks like C809 just filters the output of a buck-boosted rail for the LED backlight, so its capacitance can likely be increased a little, if that helps with finding a replacement cap easier (50V/100uF is a pretty standard value).

On using the bodge wire:

I'm quite confident that I made contact with the PCB as well, so the bodge wire is there as an addendum - it shouldn't hurt I guess?

Yeah, in that case, it should be fine.

On the noise issue
I could not reproduce the noise after the first time I plugged it in - perhaps the plug didn't make proper contact. The monitor has been running without issues yet for some hours (also after cold starts).

What about if you completely disconnect the monitor for the wall for several hours or overnight? I'm just curious. You don't really have to do this, though. I guess if it's working, then let it be.

Strangely enough, I have a Gateway 19" monitor here that always displays gray/white garbled screen for several ON-OFF cycles, if I take it apart and happen to disconnect either the PSU board or the logic board. After that, it "fixes" itself and always works fine - even if I leave it unplugged for more than a year (it's a spare monitor I have). I never figured out what caused this, because once it starts working, it's fine. Similar issue to your noise issue? - I don't know. It could be.

[WackyWeasel]

Re: AOC E2460 PDA with PSU: 715g5361 - Monitor turns black

Hello!

After some months have passed a quick update:

The monitor started to turn off after a while again, so I exchanged the last capacitor (C809 - 33μF 100V) as well:

But after replacing it and turning the monitor back on, there were horrible color aberration (see first image).

After a while I discovered that the culprit was the flatflex cable connected to the panel - when I pressed it down manually, the color was fine again.

So I ghetto-fixed it by using some cotton wool on the connector to constantly apply some pressure.

So far everything works well again - I'll post here if there are problems again...