Dell u2412mb troubleshooting

[cyberserf]

Hello,

purchased two of these when they were on sale at Dell several years back.
had this Dell LCD for a while. worked great but not has intermittent power issues. sometimes it powers on perfect and other times after leaving it off for a while on standby it just stops working. no power on or off or light.
I have seen several videos and read about the parts that goes on this power board and it is very interesting to gain knowledge and learn and get this fixed.

to test I took out the working board from the good LCD to test voltage and continuity.

I tested the input side and it reads 170V at cap and and 170V at near transformer going to output side so I think the input side is good.
both boards have same input V.

broken board DC:
mosfet left side has 2.9V to 2.9V
mosfet right side has 16V to 16V
four diodes with gray color line
A 6V
B 5.8V
C 16V
D 16V

caps:
left side right side:
1 2.9V 2.9V
2 5.5V 2.9v
3 5.5V 16.5V
4 5.5V 16.5V
5 n/a 16.5V
6 n/a 16.5V

good board DC:
mosfet left side has 5.3V to 3.3V
mosfet right side has 24V to 24V
four diodes with gray color line
A 12V
B 11V
C 24V
D 24V

caps:
left side right side:
1 5V 5V
2 5V 5V
3 12V 24V
4 12V 24V
5 n/a 24V
6 n/a 24V



Can someone please guide me on next step?
why are the reading less on the defective board when not working?
what part could be causing the voltage to drop like this?

Thanks!

[cyberserf]

Re: Dell u2412mb troubleshooting

sorry by mosfet I meant power IC. both IC's have been replaced. no diff
there are also 3 mosfets on this board.
waiting for ESR meter which is on order.

[Gabriel]

Re: Dell u2412mb troubleshooting

I have fixed a handful of these monitors and it was always the same blown fairchild 278r12. There are two of them on this board and since the lower 278r12 is used for providing power to the external dell speaker which we dont use I just removed the broken one and fitted the lower one in it's place.

[cyberserf]

Re: Dell u2412mb troubleshooting

I have fixed a handful of these monitors and it was always the same blown fairchild 278r12. There are two of them on this board and since the lower 278r12 is used for providing power to the external dell speaker which we dont use I just removed the broken one and fitted the lower one in it's place.

Thx Gabriel. I have ordered a few and will update after soldering if they are able to fix the issue.