iMac A1225 startup issue- power supply or logic board?

Hi All,

I've been researching for a couple of days in these Apple forums as well as iFixIt forums, and haven't found a thread where someone was experiencing what I am with my iMac A1225 (Early 2008). When I try to startup the iMac by pressing the power button, the iMac will get halfway through the startup chime and cut out. It will lose all power and will become unresponsive to the power button, until I unplug the iMac, wait a few seconds, and plug it back in.

This lead me to believe it was a power supply issue, so I opened it up to take a look at the LED indicators. LED 1 is on when I plug the A1225 into power. I press the power button and LED 2 lights up, LED 3 goes on for a fraction of a second, and halfway through the startup chime, the whole computer loses power and all LEDs go out. I unplug the computer and plug it back in, and LED 1 is on again. Since LED 2 turns on for a few seconds, does this mean I have a logic board issue? Or is it likely the power supply?

I have visually inspected the power supply and don't see any signs of damage or blown capacitors. I have a multimeter, but am unsure how to use it for testing the power supply. I don't know where to begin on testing the logic board. I'm guessing it would be easiest to first order a replacement power supply and try that and then try a replacement logic board.

If anyone has had a similar experience and has any insight or advice, I would appreciate it!

Thanks,

Gugineal