iMac 820-2733-A won't power on

[protocold]

Used known good PSU, Diagnostic LED1 will intermittently blink after a few try but won't stay on...

where should I start?

 

[2informaticos]

Check diode mode to ground on all secondary power supplies (big coils).

 

[protocold]

i can only find a few big coils but they dont seems to have short..

Here are some measure of voltages:

PP12V_G3H = 12v
PP3V42_G3H = 3.4v
PP12V_S5 = 12v
PP5V_S5 = 5v
PP3V3_S5 = 0v. (NO short to ground)

 

[2informaticos]

Try changing U7700.

 

[protocold]

ok U7700 replaced, now LED1 is on. I now have PP3V3_S5.

However, it wont respond to power on if I short J5010.

I saw SMC_ONOFF_L goes low from 3.4v to 0.3v when i short J5010.