Acer 4K monitor troubleshooting

[fiskmaas]

Hey EEVblog forum,

So I'm trying to diagnose what could be wrong with my monitor. It's a Acer xv273k, the problem is that it blinks black every ~500ms. Here's a video of the problem: https://imgur.com/a/UcL3sEb

So it's definitely a monitor problem, it persists on OSD and on different inputs. I'm wondering if anyone knows what it could be, or how to troubleshoot. I'm not very experienced with troubleshooting electronics like this, but I have all the gear required (cheap oscilloscope, multimeter etc.) and experience soldering.

Any and all help welcome as I was hoping to get some more time out of this thing, warranty expired just 6 months ago

Thanks!

[wraper]

Seems to be a backlight issue as image seems to persist when backlight disappears. Probably protection kicking in and backlight restarting. Could be a problem with backlight driver or an issue with LED strips which causes protection to kick in. Try adjusting brightness setting and see if it changes anything.

[n4u]

Yea.. You may additionally  check with flashlight - it should be visible image when you highlight the screen. I will start with temperature of inverter and capacitors.

[fiskmaas]

Thanks both for your quick answers.

Seems to be a backlight issue as image seems to persist when backlight disappears. Probably protection kicking in and backlight restarting. Could be a problem with backlight driver or an issue with LED strips which causes protection to kick in. Try adjusting brightness setting and see if it changes anything.

Yep, lowering brightness seems to fix it for the time being, going above ~60% will make the blinking start again. Does that indicate something specific?

I also tried the flashlight and it seems to just be the backlight. Image is constant.

[Traceless]

I'm going on a hunch here and say this is a power supply problem. I've had similar issues with Samsung screens. Does the power LED go slightly dim when the backlight cuts out?

[fiskmaas]

I'm going on a hunch here and say this is a power supply problem. I've had similar issues with Samsung screens. Does the power LED go slightly dim when the backlight cuts out?

I will check if the problem comes back. Now the problem won't come back, obviously because I'm trying to get it to come back. 

Another thing I could add is that it usually happens in the morning after the screen has been off for a while. Yesterday it went away after a while, and it seems to be the same today.

[wraper]

Another thing I could add is that it usually happens in the morning after the screen has been off for a while. Yesterday it went away after a while, and it seems to be the same today.

While electrolytic capacitor failures are not nearly as common like a decade ago, it's probably the issue with such symptom. When capacitor heats up, its ESR becomes lower which may cause the issue to go away when it warms up, but not for long until capacitor fails completely.

[Traceless]

Keep an eye on it. If this is similar to the problem I have in mind a component in your PSU is marginal and will cause the supply voltage drop under a critical threshold (which may cause the power led to dim down slightly). The feedback circuit will detect that and restart the supply. This will repeat, eventually the power supply stabilizes and stay on if you don't turn it of. In my experience the component degrades exponentially if you power off the screen and let it settle for a while. So basically what will happen is: First it flickers once and then just works. If you switch the screen off for a while and turn it back on it will flicker twice, next time ~4 times then ~8 times and so on until it will not stabilize at all any more.

[fiskmaas]

Another thing I could add is that it usually happens in the morning after the screen has been off for a while. Yesterday it went away after a while, and it seems to be the same today.

While electrolytic capacitor failures are not nearly as common like a decade ago, it's probably the issue with such symptom. When capacitor heats up, its ESR becomes lower which may cause the issue to go away when it warms up, but not for long until capacitor fails completely.

How long is that usually? Are we talking 20 minutes or could it be 3+ hours? Because yesterday it went away pretty quick (1 hour or so) but today it might have been 3-4 hours.

Keep an eye on it. If this is similar to the problem I have in mind a component in your PSU is marginal and will cause the supply voltage drop under a critical threshold (which may cause the power led to dim down slightly). The feedback circuit will detect that and restart the supply. This will repeat, eventually the power supply stabilizes and stay on if you don't turn it of. In my experience the component degrades exponentially if you power off the screen and let it settle for a while. So basically what will happen is: First it flickers once and then just works. If you switch the screen off for a while and turn it back on it will flicker twice, next time ~4 times then ~8 times and so on until it will not stabilize at all any more.

Ok, will check. The problem is usually pretty constant, ie. not doubling like that, just consistant ~500ms on/off.

[Traceless]

@fiskmaas: It might be a bit different for you since you have an Acer unit, not a Samsung. Someone documented their troubleshooting process for a faulty Samsung supply (see video below). For for those Samsung screens it is easy to diagnose because they use an external DC power adapter so you can just swap the faulty one or hook up the screen to a bench PSU. I assume your Acer has an integrated supply with IEC-cord?

[fiskmaas]

@fiskmaas: It might be a bit different for you since you have an Acer unit, not a Samsung. Someone documented their troubleshooting process for a faulty Samsung supply (see video below). For for those Samsung screens it is easy to diagnose because they use an external DC power adapter so you can just swap the faulty one or hook up the screen to a bench PSU. I assume your Acer has an integrated supply with IEC-cord?

No it's an external PSU aswell. I don't have any PSU that's equivalent I think, but I'll check.

[fiskmaas]

So I removed the cable from the power brick for about 1 hour, and flickering started when powering up again. The power LED did not flicker at all, so there's that.

I'm assuming it's not the PSU. Can I troubleshoot further to narrow it down somehow? Someone mentioned inverter/cap temps.

[Traceless]

... The power LED did not flicker at all, so there's that. I'm assuming it's not the PSU...

Unfortunately you can't rule out the power supply yet. While the LED dimming is an indicator for a problem with the PSU, just because the symptom doesn't show on your unit doesn't mean the power supply is okay. Getting a spare DC-Adapter for the screen might be the easiest way to proceed. Sometimes replacements from the original manufacturer are pretty expensive. In this case you can look for aftermarket ones on amazon. If you have a multi-meter you could check the DC-adapter's output voltage and see if it matches the specified voltage. If it is too low this points towards a faulty supply. However even if you see the correct output voltage that does not necessarily mean the PSU is okay (because you are measuring without a load).

[fiskmaas]

... The power LED did not flicker at all, so there's that. I'm assuming it's not the PSU...

Unfortunately you can't rule out the power supply yet. While the LED dimming is an indicator for a problem with the PSU, just because the symptom doesn't show on your unit doesn't mean the power supply is okay. Getting a spare DC-Adapter for the screen might be the easiest way to proceed. Sometimes replacements from the original manufacturer are pretty expensive. In this case you can look for aftermarket ones on amazon. If you have a multi-meter you could check the DC-adapter's output voltage and see if it matches the specified voltage. If it is too low this points towards a faulty supply. However even if you see the correct output voltage that does not necessarily mean the PSU is okay (because you are measuring without a load).

Allright, I checked with multimeter. Output is 19.5V. Rated 19V, 7.1A. Not sure I have anything that high voltage/amperage that I can swap with to be sure, but output looks ok at least.