iMac 24" 2007 boot loop, what to do?

[dsudorion]

A while ago I received an old iMac from a friend of which the HD was broken. The machine was covered in a thick layer of dust, so badly the CPU/GPU fan was completely stuffed. So I decided to remove all the parts, and brush them clean. As a result of this dusty mac it also had the classic brown spots on the screen.

So after cleaning this little menace I assembled it again with the result of.. a boot loop.
LED#1 lids when plugged in, when pressing the power button LED#2 and #3 show (without the screen installed) and after 2 seconds it goes back to LED#1 to repeat the procedure until I pull the plug. I "baked" the Logic board and after that it got it to work for 1 day. So I wonder.. I don't expect the PSU to be broken, because when I hold the power button it stays on longer and the fans kick in overdrive.. anybody had a similar situation?

btw, cleaning the LCD is, in the end super easy. I once saw a video on youtube (and about the only one online) of a guy doing the same with a 27" LCD.

 

[dsudorion]

Nobody has any advice?

 

[DeltaMac]

You said that you are trying to boot without the LCD panel installed.
Do you mean that you expect it to completely boot without the LCD panel plugged in?
Be sure to try that with the LCD panel plugged in.
Anyway, #4 LCD means that the video card and the LCD panel are successfully communicating, and you should have some kind of image on the screen, even if very dim.

If the #3 LED comes on only briefly, then goes back to #1 LED only, then could be the video card, BUT,
with the evidence of fairly poor cooling for likely a long time probably means that the power supply has been really "stressed". If the power supply can't hold power for very long, then one of the first things that will quit is the video/LCD, as that needs a good bit of power to light up. Part of that symptom is that you could finally get it to work, at least for a few hours. You should try a different power supply as a troubleshooting step.

While you are cleaning, be sure that the small cooling inlet on the back, just above the power cord, is clear. That's a place that some users miss

 

[dsudorion]

Hi there, yeah, I'm trying to boot without the panel, since I expect the 3th LED to burn and after that install the panel. I will give it a try with the panel installed but I'm not sure it will make a difference. I also suspect the PSU to be done for, especially since it didn't have a chance to cool with a clogged fan. I suspect the PSU won't be fixed with a reflow?

And yes, the HD cooling inlet looks spic and span, sorta

 

[dsudorion]

Oh and, I did try to boot it up with the LCD panel, which resulted in a black screen without the booting sound

 

[DeltaMac]

Might be bad RAM. Remove all RAM (so the slots are empty), then try to boot.
If you get a error beep (not a boot chime, but a beep) with NO memory installed, then try some different RAM, or just try one stick in one slot at a time, making sure to seat it fully.
If you still get no video, and no boot chime, make sure that the fans are running, indicating SOME power to the system.
Could still be a power supply, but maybe more likely now is a logic board, with a failed chip somewhere. That will be beyond a "reflow".

 

[dsudorion]

Hi there, I know the RAM should be fine. it has 2GB + 4GB and without them it indeed beeps. Installing only one (the 2 or 4) it still results in the same reboot loop. The chime does not happen since it reboot before it gets that far.

But I am indeed suspecting the PSU. Today I heard a very mild ticking sound coming from the PSU. Which doesn't very good. Unless somebody installed a time bomb there..