Ok. I've read all the posts about the Power Supply and the LED tests etc. My problems have been unique and intermittent

About a month ago, my iMac was in SLEEP mode. I went to wake it up with a keystroke or mouse move (not sure which) and it simply turned off. No shutdown, the light and power went “out.” Dead.

I went to power it up and it had no response. Annoyed and upset, I went to sleep and left it all night. The next AM – being new to the iMac diagnostic world – I found instructions on and executed a reset. It took a few tries but it came back. I put the incident behind me.

Then a few days later, it happened again. Same sequence – system dies on sleep “wake up.” This time I was more in tune with the procedures. So I did the reset of the Power unit (again – unplug from wall, wait 15 seconds, plug in, wait 5 and power up.) On these tries I had weird results:

• First' (try) – nothing;

• Second – white light and drive motor sounds for about 2 seconds, then stops dead;
• Third – white light and drive motor sounds for about 4 seconds then dead;
• Fourth – it boots and sits on grey screen. (NOTE: this was the only time it sat on grey screen. ) After this last try I put the System disk in and she booted up.
• Concluding actions after booting - I ran diagnostics on the hardware – all GOOD; I ran Diagnostics on the drive – all good not repairs needed.

Yesterday she was dead again (same sequence.) On FixIt and MacSupport I’ve read many of the posts. I opened her up. Got familiar with the insides. Tested it open and she booted back up ok. NOTE: I could not find the LEDS on this unit while it was dead and open. But when she came back to life when the cover was off, I could see the LED under the tape. Thus – I can assume – when the system was “dead” we had NO LED ACTIVITY AT ALL. And when she was working yesterday I did a few cycles of Power off through the OS and turning back on. During this sequence when when it was off – we had 1 LED working. But…….. (finally and I am almost done.)

She died again yesterday evening. And NO LED at all when plugged in.

Conclusion as of this 12-13–2011

I ordered a new Power Supply. Seems as the time of failure is increasing, the PS is having issues. Hope to install tomorrow or Thursday.

Does anyone think its something other than the Power Supply? Can this be a logic board issue? (I hope not.) ''italic text''

Can we assume that the “startup” issues I noted above where it would start for 2 seconds then stop are related to needing sufficient boot up voltage? This is where I am going but any input would be appreciated. And I will update the posting as I get the new PS installed.

Update

UPDATE:

The Imac failed a few days ago. I installed the NEW Power Supply today. I got the green light and its booted up fine. I will monitor it for the next 2 weeks and update my post. I agree it most likely is solely a power supply failure and nothing more. But will update the post should the same symptoms come back. Happy Holidays.

FA