Chosen Solution
Just tested my dead iMac Intel dual 2.4Ghz PSU. It currently doesn’t boot, no signs of life. After looking at the pinout voltages on here I see pin 8 should read 12V. I have the 3.6V on pin 5 but no 12V rail. Is it likely the PSU is shot. I had somebody elese test it and they said it was OK but I am wary of their motives. i.e. Replacing the logic board as a repair instead of swapping out the PSU. Any pointers would be great. Thanks Chris
What are the last 3 characters of your serial number, please? That way we can define your exact machine. Weak/bad power supplies can have all the correct voltages, but not be able to handle the current draw. Your 12v rail is missing then LED 2 will not be lit. With a totally dead machine you need to start with what the diagnostic LEDs say The diagnostic LEDs to the right of the RAM slots (this may be covered by a piece of black electrical tape). LED Startup Sequence LED #1 = Power available. If no LED is visible: • Verify AC source • Verify known-good AC cable is connected • Verify cable connection between AC inlet and power supply • Verify cable connection between power supply and logic board • Verify power supply LED #1 + LED #2 = Power available, and system is powered on. If second LED is not visible when power button is pressed: • Verify power button connection to logic board • Verify power button functionality • Verify cable connection between power supply and logic board • Verify power supply • Verify logic board LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found. If third LED is not visible after power on: • Verify that MXM video card is seated properly • Verify logic board If no lights are coming on you need to replace your power supply. A trickle charge is sent from the power supply to the first LED. If the first LED is not lit the power supply is not working. If the power supply is weak and can’t sustain the system, the LED 1 will be lit, LED 2 should blink when the power button is pressed - but may not light at all. I would look to the guide Richdave put together for your pinouts. - iMac Intel 20" EMC 2210 Power Supply Output Voltage Test
If not done already - check the cable between the PSU and Logic board is seated correctly, and that no pins have been pushed out of the connectors. This could explain no LED 1.
Also you may want test each wire in the cable with a meter - there are reports of this cable failing. (again assuming I have ID’d the correct model) Check the part number on the cable near the logic board connector - if its 922-8188 it’s the new type cable. If it is not visible then it is likely the older (less reliable??) cable. TBH the more I think about it the more convinced I become that no 12V at pin 8 is a terminal indicator for the PSU. Hope I’m wrong.
