Hi all. Can someone help me troubleshoot a problem with an iMac I recently obtained from a fellow ehmac'er thinking (foolishly) that I would probably be able to fix it myself?
When cold, the iMac boots and runs normally.
I have no hard drive installed so I am just booting off the MacTestPro CD for this machine.
Once the iMac warms up (approx. 20-30 minutes), the screen will power off (you can hear it power down) and the power light on the front will start to pulse a dim green. You can also hear a slight clicking as the power button brightens and my optical mouse flashes on at the same time as the power button pulsing.
So far I have tried reseating the RAM, changing the battery, and resetting the PMU. When running the MacTestPro tests I do not see any failures although the test never gets a chance to complete before the iMac warms up and shuts down.
Once this happens, I need to let the iMac completely cool down before I can start it up again. Then the cycle starts all over again. If I unplug the iMac and wait 10 seconds then try starting again, the green light comes on but the iMac does not make any sounds like it is attempting to power up.
As this is a heat related problem I am thinking that there may be a logic board problem or a bad solder joint somewhere that only affects the unit when it warms up. My only problem is I do not know the first place to look to try to eliminate this and given the cost of replacement parts, I can't afford to start buying and swapping parts to see if the problem goes away.
Your iMac is at death's door and there isn't anything you can do to fix it that is cost effective considering the cost of the iMac. The only cure for this is a new PVB board.
I tried the exact same repair with the exact same issues on another "dying" iMac 400 and I removed the PVB, resoldered all the connections but the final issue is with one capacitor that you cannot purchase from your electronic supplier (don't ask me which one as it's been a while but a google search should help you discover this). I tried installing cooling fans, modding the case for better cooling, nothing stopped this problem.
So, I basically gave up stripped the system down and sold the parts on eBay and bought another one that didn't have the problem with the proceeds.
the crap is piled high ... now trying to keep up
I finally took the cover off last night to determine if it was Rev. 1 or Rev. 2 PAV board. I verified that it is the Rev. 1 board. Apple part number is 661-2212. If anyone comes across one of these anywhere let me know. I am watching ebay for it - there were a few sold a while back but at that time I did not know which one I needed.
This probably won't help but... make sure you have updated the firmware as there are all kinds of weird power and screen issues that will occur if you don't update the firmware on these iMacs before upgrading to OS X. I don't know if the MacTest CD is running OS X or not but try the update... although it may be hard to install it without a HD.
Thanks but that's what made me buy this mac in the first place. I was hoping that it was a simple software issue but alas, it was not. The Mac Test Pro CD I have is OS 9 and the first thing I did was check the firmware rev. and it is definitely 4.1.9. I also installed OS 9 on the hard drive and surprisingly the mac did eventually run well for more than 2 days before crapping out again. I am 99.9% sure that a new PAV board is the only cure but of course as the first reply suggests, this might be just the start of more to come with this machine.