820-2828-A iMac 27" 2011

[lincev]

hi all, I have this board with a power problem, I connect the power cable and LED1 ON, I press the power button and LED1 turns off and when I release the power button it turns back on. It seems to have a short to ground.

I have tried another power supply and same problem

problem GPU or CPU? replace Q8110? or any ideas?

 

[2informaticos]

Did you check diode mode to ground on all secondary power supplies?

If 12V_S5 drops, change Q8110.

 

[lincev]

sorry I don't cheack all secondary power supplies

i have short to ground at line PP12V_S0 and 12V_S5 drop to 6v 5v etc..

change Q8110?

 

[2informaticos]

Not yet.
Find what causes the short on 12V_S0.
What is the exact ohm value?
Compare with values on the big coils.
You may have shorted MOSFET on CPU power supplies.