820-00430 No Power

[CRC2018]

Got a bit of a strange one here 820-00430 iMac 21.5" Logic Board.

We have replaced the PSU in this iMac previously a few months back but it has been brought back in with no power - no lights on the logic board but the PSU is outputting 11.85V and PP12V_G3H is present. PP12V_S5 is not however.

I'm using the schematic for the 820-00034 board as I cannot find one for the 820-00430 - would I be correct in assuming that Q6970 is a likely culprit? My only confusion is that Q6970 on the schematic is a 3 leg IC but on the board itself the IC in this position appears to have 8 legs?

 

[2informaticos]

Such difference is usual for Apple, since old schematics.
Just use the power rail and signal names to locate into boardview; or surrounding components.

12V_S5 MOSFET fails a lot on iMac boards.
Is the first to try.
Be sure no short to ground, on its output.

 

[CRC2018]

Ok so i heated the 12V_S5 mosfet and it worked for a bit then stopped again. I've now replaced it and the iMac is working normally again.

Thanks for the advice!