APPLE iMac (21.5‐inch, Late 2013) 820-3588-A not turning on, faulty PS?

[mexbeb]

Ciao a tutti! I was given an old late 2013 iMac that doesn't turn on. I have the .brd file and the schematics and I've done a little analysis on the boards. Starting from the PS it appears to have 11.6V instead of 12V and that is a little strange, isn't it? Measured test points for PP12V_G3H and gives me 11.6V as well.

The iMac have two different types of behaviour:

1) no button pressed when inserting AC cable; inserting AC cable turns LED #1 on, when pressing power button LED #1 turns off for half a second, then turn on again, LED #2 turns on for half a second and then turns off;

2) pressing power button when connecting AC plug; no LEDs for 4-5 seconds then LED #1 turns on, LED #2 turns on for half a second and the fan seems to start spinning for half a second, then LED #2 turns off and fan stops spinning.

Could it be a power supply problem? What else can I test to be 100% sure?

[mexbeb]

Re: APPLE iMac (21.5‐inch, Late 2013) 820-3588-A not turning on, faulty PS?

Ciao a tutti! I was given an old late 2013 iMac that doesn't turn on. I have the .brd file and the schematics and I've done a little analysis on the boards. Starting from the PS it appears to have 11.6V instead of 12V and that is a little strange, isn't it? Measured test points for PP12V_G3H and gives me 11.6V as well.

The iMac have two different types of behaviour:

1) no button pressed when inserting AC cable; inserting AC cable turns LED #1 on, when pressing power button LED #1 turns off for half a second, then turn on again, LED #2 turns on for half a second and then turns off;

2) pressing power button when connecting AC plug; no LEDs for 4-5 seconds then LED #1 turns on, LED #2 turns on for half a second and the fan seems to start spinning for half a second, then LED #2 turns off and fan stops spinning.

Could it be a power supply problem? What else can I test to be 100% sure?

EDIT:

Now I have no LEDs at all, I measure 11.6V at 12V pin on the board and no more PP3V3 or PP3V42. Is still a PS fault o do I killed the logic board? LED #1 went off when I was measuring U6970, I measured PP12V on pin 1, SMC_PM_G2_EN (3.4V) on pin 2 and then poof, no leds. Maybe a short between PP12V and SMC_PM caused by the DMM?

[mon2]

Re: APPLE iMac (21.5‐inch, Late 2013) 820-3588-A not turning on, faulty PS?

I would consider to source another power supply for at least testing. There are high voltages on this power supply so be very very careful. Best if you cover up the back side of the PCB with cardboard and tape so there is no shock hazard before testing.