Asus LS221H - Power LED is blinking

[-k2-]

Hi,
I've trouble with my Asus LS221H LCD Monitor.
When i put in Power, the Power-LED is blinking. I can't switch off the monitor.
I've disconnected the CCFL board => same problem.
I've disconnected the Screen => same problem.
I've disconnected Screen and CCFL board => same Problem.
So the fault is probably on the board in the stand.
I suspect one or both regulator "1084 PE 025H1" are faulty, because I can hear a very faint whistle from the field.

Has anyone an idea how I can check this, or what else could be faulty?
I have a multimeter (Amprobe AM-240)

I thank you in advance for the help.

[budm]

Re: Asus LS221H - Power LED is blinking

I would check those cap for capacitance and ESR. The TOROID with blue core is switching power supply with two caps next to it, check those caps also, that TOROID is more likely the one that is making noise. Have you already verify that the external power supply is OK?

[-k2-]

Re: Asus LS221H - Power LED is blinking

I've checked the two caps.
They should have 330uF, and they have 359uF and the other one 360uF.
I don't know how to check ESR with my Multimeter (AFAIK i need an ESR meter for that).
External power supply is ok.

[-k2-]

Re: Asus LS221H - Power LED is blinking

I've added a mp3-file (packed as ZIP-File). There You can hear the "whistle" (and Background noise).
It's around the "1084 PE 025H1" regulator. I can't locate the exact position from where it comes, because it´s really very faint.

I also measured a little, and found that at Q2 and Q15 the voltage jumps between 3,34 and 0V. In the same clock as the whistle.
I've added a picture, with the voltages from Q2 and Q15.
All but power supply disconnected. It's the same.
(PS: sorry if my english is nod good, but i think You'll understand what i mean)

[-k2-]

Re: Asus LS221H - Power LED is blinking

I've changed all the caps (4x330uF 4x100uF).
So we can exclude these.
I have measured some voltages (see pictures).
[e.g. 3.34V/0V means, that the voltage jumps between 3.34 and 0V]
Maybe it helps somehow.
I already fear that the EEPROM or serial flash is faulty.