Help! Power Mac G4 powers on but doesn't boot.

[Steve]

I have a Power Mac G4 MDD/FW800 (dual 1.42 CPUs) that powers on but doesn't boot. The system turns on, no video on screen, no startup sound, the power button's light turns off, and after a few seconds the CPU fan goes from low to full blast.

This did not start until after I took off the heatsink and put some Arctic Silver 5 on the CPUs.

What I've tried: Made sure the heatsink was screwed down tightly, that RAM and video card were seated firmly, tried booting with Cmd+Opt+P+R, tried booting with Ctrl+Alt+Shift, tried booting with Shift, got the battery checked and tried resetting the PMU.

Help!

 

[TheStu]

Well, I suppose it is possible that you fried the mobo or CPUs with a static discharge. Or you could have over-tightened the heatsink. I think you may have killed it.

Only other Macs that I have seen with similar issues were also dead.

 

[Compman55]

I know this will sound stupid, but tear it all aback aprt and spray all the AS off with a product at autozone called "QD Electronic Cleaner". Then apply just plain old white thermal paste and put back together. AS is very conductive, it is possible certain things are being shorted out with it. Also the G4 as a very odd CPU card socket, make 100% sure it is clean and well seated.

 

[Steve]

I'll see if I have any of the white stuff. I don't know how to seat or unseat the CPUs or their daughterboard.

 

[Compman55]

You will find out soon enough.

 

[Steve]

Figured out how to unseat and reseat the CPU daughtercard, cleaned off the heatsink and CPU cores with 91% isopropyl alcohol and applied white thermal paste. No change. I'll see if I can find that cleaner from Auto Zone this weekend.