Imac A1311 late 2009 820-2494A

[ex250]

Hello guys, I have this one with a non-starting failure, on board diagnostic led 1 lights ok, tested other know working power supply to discard, same behavior.

The board is the 820-2494A

the S5 lines read:

PP1V1_S5_REG -> 1.11V

PP3V3_S5_REG -> 3.37V

PP5V_S5_LDO -> 4.98V

PP12V_S5 -> 12.01V

Seems all ok

This ones not, too high readings, maybe the same culprit:

PGOOD_1V1_S5 -> 3.37V (should be 1.1V?)
5VREG_EN -> 3.37 (should be 5V?)

I was thinking that the U7300 could be the problem, but replaced and all is the same.

Any one could point me some direction? Quite lost with these boards.

Thanks!

[ex250]

No body?

[reformatt]

The 2nd LED on these only comes up when PP3V3_S3 is on, which in turn is enabled from PM_SLP_S4_L. You need to go through the pre-requisites for this signal to be generated from the PCH.

Whilst this is doable, troubleshooting these boards outside of the iMac requires a jig of some nature. Is supplying 12V to the main power input enough from a bench supply? Maybe, but given the age of these things now, I refuse to fix mainboard faults on them.

[ex250]

Sorry for the delay, quite lost on this board. The 12 V supply is ok, tested with 2 different know working power supplies.
It's not quite clear for me how to check PM_SLP_S4_L