Chosen Solution
iMac 21.5” late 2009 EMC 2308 A couple days ago I discovered the machine was off and would not power on. Don’t think we had a power surge or anything like that - nothing else in my home was affected. So far have tried several fixes. Swapped the AC power cable. Nothing. So I opened up the machine and… Checked the Diagnostic LED’s. Light #1 comes on when the machine is connected to AC power. Light #2 does not come on when the power button is pressed.Checked the logic board test pins:Pin 4 (Standby Power) - 12V OK!Pin 11 (Run-Mode Power) - NothingPin 12 (Power On Request) - NothingChecked the power button by testing for continuity between the two pins on the power button cable. Seems to be working properly (infinite resistance when not pressed, zero resistance when pressed).Swapped the power supply - NothingSwapped the DC-In cable - Nothing Is the only remaining step to replace the logic board? So far the parts and attempted fixes have been pretty cheap. I’m not sure I’ll want to buy a new logic board. Is there anything else I should try? I can’t find any other recommended fixes or troubleshooting steps. Thanks!
Sorry I did not spot your question when you posted it. All #1 LED indicted is that you have power to the power supply. Just replace it: If it fails to work, return the part. iMac Intel 21.5" (Late 2009-Mid 2011) Power Supply iMac Intel 21.5" EMC 2308 Power Supply Replacement
Old post, but there I go anyway… I had two of these iMac model in my hands a few months ago, and both had same problem. Before finding this thread, I did everything you already said , and tested components from one to the other with no success. I’m afraid there is an unknow problem with this motherboards. An interesting fact is that the iMac that failed on this issue have been those with AMD graphics. The models with NVIDIA integrated graphic have not given any problem of that kind I’ll stay over here if there’s any update
