Chronic wake/boot problem for G4 DP 500

Greetings,

I've had this problem since the day I bought my computer, and none of the solutions I've been able to find have worked. So I'm looking for either someone that has actually managed to fix the same problem, or (more likely) confirmation that I'm screwed and should have had it replaced under warranty when I still had one.

Problem:

Computer (powermac g4 dual 500 mhz) won't wake from sleep about 40% of the time, and doesn't cold boot every once in a while (more rare, but same situation)

Symptoms:

Fan comes on, but no HD spin up, no video, no response to anything but a power-button-reset (the soft reset button doesn't work).


Failed solutions:
-resetting Parameter RAM
-resetting NVRAM (open firmware)
-reformat/replacement of HD
-multiple OS upgrades (running Tiger now - no help)
-unplugging ALL peripherals

I've done all I know to do, and haven't had any luck. Also, it should be noted that the original HD (IBM 40Gb) started having problems (bad noises/spin down) and was replaced by a drive that eventually started having problems too (incurable bad sector - found a "serviceable used part" sticker on it when I pulled it yesterday): I don't know that this is related, but I'm just the slightest bit concerned that whatever is causing the sleep problems may also be destroying drives, which is a fate i'd like ot avoid for the fresh 80Gb maxtor that's in there now.

Anyway, this problem has frustrated me for years, and has prevented me from using sleep at all. I've really enjoyed this computer, but man-o-man am I ready to see this issue go away. Help is greatly appreciated.

Thanks,

I did try resetting the PMU: the battery voltage is still within range, and it seems to me like problems would manifest themselves differently if that were it. I may try slapping a new one in there just to completely eliminate that possible problem source, but I'd be really surprised if that did it.

It may be worth noting that I tried resetting hte PMU again yesterday, and was able to sleep and wake the computer about 5 times before it failed to wake on the 6th attempt: I'm guessing this is just luck of the draw with about the same odds as before, but if you guys think that means anything, I'd love to hear it.

Still looking for the real problem here.

No other ideas?

I haven't done any RAM swapping, but I have run a few system-wide diagnostics, including Techtool Pro, which didn't return any problems.

Is the RAM really something that would effect this? I'm fairly sure that when the computer fails to start or wake, it's because the primary HD never spins up, which would seem to me to be something like a Logic Board Issue. And correct my if I"m wrong here, but when I removed the battery and hit the PMU reset button, everything on it was reset. I'd think my next step is to hunt down a new logic board, but to my eyes this seems to be integrated into the motherboard on this model, and thus not an insignificant repair.

Let me know about the RAM: i haven't tried it yet, and I will if it's really a potential problem.