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I got Philips 190V as a gift, which would be a nice replacement for my old AOC 9K+ which consumes a lot of power by my calculations.
I have a lot of experience with electronics, and LCD monitors, but this one is a mystery to solve.

The problem: The monitor turns off after a few seconds, power LED also turns off, and then turn on again, works well a couple of seconds and goes off again, and as always the power LED together with him, and so a couple of times or infinitely...
Then sometimes happen that it will not work anymore until I press button ( any except Power ) and works as long as I hold the button, as soon as I let it extinguishes.
There are also other symptoms: So for example, sometimes starts blinking together with power LED and then turns off and stays off until I turn it on again by pressing the power button. Then sometimes happen that it will not work anymore until I press button ( any except Power ) and works as long as I hold the button, as soon as I let it extinguishes.
Sometimes it just works, but suddenly menu opens...
Then sometimes, it works, but if I press any button, it will turn off and will stay off until I release the button. Power button works very rarely.
I figured out that the problems gradually weaken when it is well warm . Sometimes working at 2 -3h and suddenly problems start again.
Also, sometimes, when PC is off, it doesn't want to go sleep, it just shows "No video input"... But that's not important to fix.

I disassembled it, power board gives the OK voltages even when the problem is happening. For my visual inspection, it looks fine. Video board also looks right. Neither the one nor the other, no inflated capacitors.
I checked the main filter electrolytic capacitor at high voltage section and the output filter electrolytes (2200uF x2) at the low voltage section, with my primitive method of measurement, without appropriate instrument and using just a multimeter - These capacitors seems like OK.
I checked and 2-3 Low Capacity (1uF or more) capacitors on the video board, and they all seem OK. I measured the voltages on the voltage regulators, and they seem to be normal. Disconnect the front panel buttons, if they are defected, but it does not solve the problem .
I ran out of ideas, my soldering iron is broken so I only get one with a thick tip, making it difficult to de-soldering a small capacitor on the video board. Should I get one by one and test them? There is a lot of them... And with this soldering iron I'll have hard times....

Does anyone have any tips and ideas?
Thanks!

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You will need to verify every capacitor. This was a used item? If so ask the gifter if it worked. If shipped it might have been damaged in transit. –  Ramhound Feb 6 at 2:19
    
On video board? - Yes used, by my customer, which decided to not wait until I repair it, and go for new one. This monitor is 5 years old. No, it is not shipped. –  xZero Feb 6 at 2:21
    
I am pretty sure this is out of our scope here a Superuser. Your asking on help diagnosing a power issue on a circuit we don't even have access to. –  Ramhound Feb 6 at 2:23
    
I asking for only suggestion for what I should look for, from someone more experienced than me. The suggestion which helped will be marked as an answer. –  xZero Feb 6 at 2:25
    
That would not be an on topic question here a Superuser. –  Ramhound Feb 6 at 2:27

1 Answer 1

The problem cause is slightly banal, it was a front panel failure. When I disconnect it, monitor works, immediately after connecting, the problem appears.

I still don't know where on the simple front panel PCB problem is, but it contains several SMD parts - resistors and capacitors. They might be faulty. Other parts are push buttons, and 3-pin two-color LED diode.

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