iMac No Power. Is 12v & 3.3V on PSU pins ok?

Hi All,

I need help to diagnose the issue with my 2011 iMac 21.5" with i7. One day when i came back after dinner I noticed that the display was shutoff but the fans were spinning. I couldn't wake it up so i used the power button to shut it down. After that i cannot start it back up. No fans, no hdd spinning.

I've spent a lot of time in this and other looking at related threads. and diagnosed it this far

- only 1 LED lights up. LED 2,3 or 4 never light up.

- PSU doesn't show any blown capacitor or other issues on visual inspection.

- even after disconnecting the HDD, Optical drive, Bluetooth & wireless the system doesn't start.

- SMC reset doesnt' do anything to help the situation

- logic board doesnt' see any issues on visual inspection.

- All heat sink/fan looked clean without much dust that could indicate a cooling issues

I want help to identify if this is a PSU or Logic board issue. I couldn't get a authoritative pinout diagram for this PSU. I am only getting 3.3 v & 12 v on some of the pins (don't have the exact pin # but i can post later). Not getting any 5v on any of the 14 pins. Also some of the pins don't show any voltage.

I know the ATX powersupply for older pc had a 3.3v along with 5 & 12. What's the deal with the iMac. Are those readings i'm getting correct?

Or is my PSU busted (at this point i'll be glad if that's what it is) given this happened 3 months after i ran out of apple-care.

Any help greatly appreciated.

here is the voltage that i'm seeing on the various PSU pins

• 1 - GND
• 2 - 3.3v
• 3 - 12.1v
• 4 - 12.1v
• 5 - 12.1v
• 6 - 12.1v
• 7 - 0v
• 8 - 0v
• 9 - 3.3v
• 10 - 0v
• 11 - 12.1v
• 12 - 0v
• 13 - 0v
• 14 - 0v