820-3588 First LED blinks after power button press

[No-Clean]

Clean board, no shorts found on any of the rails from page 100.

All test are done with board alone and PS set up at 12.2V like I always test this boards, with iMac PS does the same thing.

Already replaced Q8450 and U7600.

I have steady PP5V_S5, PP3V3_S5, PP3V42_G3H

Not sure what else to check.

 

[2informaticos]

Change Q6970...

 

[No-Clean]

Done, but same behavior.

 

[2informaticos]

Did you set PSU amp limit to max first?

 

[No-Clean]

Yes and all the donor parts are coming from a working board that I was able to power on with PSU

 

[2informaticos]

If 3V3_S5 is really stable, first LED can't blink; it is driven directly from 3V3_S5!!!

 

[No-Clean]

First LED is steady green, it blinks only when power button is pressed or if power on pads are shorted.

 

[2informaticos]

You've said steady 3V3_S5; seems not, probably didn't note drop pulse.
Should be good to use o-scope to monitor 12V_S5 also, at same time.