G3 iMac shuts down

[Rich Wiebe]

my son's G3 iMac shuts down for no reason at all
it will start up, run for about a minute, then completely turn off
trying to restart immediately gives no response at all
but unplugging and waiting a few minutes allows it to start, but then after about a minute it will shut off completely

i think it is a bad motherboard

anybody else have any ideas?

[PrintIT]

Heat issues maybe?

[Rich Wiebe]

okay - the dissipation of air cooling not always great - may be some dust in there to boot

[tnelson@bexx.com]

If it is a hardware problem it likely will be logic board or power supply. Most likely logic board as I haven't seen too many power supply failures on first gen iMacs. Can you run it long enough to look at the crash log?
You can try some resets:
on boot hold down "command-option-o-f" keys / you will get a command line screen / type "reset-nvram" and then "return" / then type "reset-all" and then "return"
When you do this the computer will reboot.
In addition you can reset Parameter RAM at this time by holding down "command-option-p-r" - let it reboot a couple of times. I suspect you've got a logic board problem but these are painless trouble shooting fixes.

If you want to poke inside the iMac, take off the RAM cover. Looking inside from the back of the iMac, to the right of the the RAM slots you will see a small button. Using something non-conductive, press it once. The button is a logic board reset and I have seen it solve powering off issues a couple of times.

theo

[Rich Wiebe]

i tried to power it on and it stayed on for about 2 seconds (not booted and running, but just the light on) the first time
then i had no response whatsoever

i had a donor imac lying around that would boot and run (shipped in poorly executed packaging by ebay seller resulted in broken screen supports)
i swapped out the logic & down-converter boards and found that the old ones were good
swapped out the divider panel with power supply, etc and had good luck

so i suspect it was the power supply

now i have a spare logic board for him, or my other son, when the next one goes out

[blackjack]

it's a Kernel Panic. The one and only OS X true crash.

Try removing all but the original RAM. i'll bet that's your culprit right there. OS X doesn't like cheap RAM.

If not, you should zap your pram, that fixes things alot sometimes.

[republic]

I dealt with lots of G3 iMacs (revs B through D) in their day, and nearly 100% of them had a specific failure after about 2 years resulting in symptoms similar to what you are seeing. The power-analog-video board (PAV board) fails and causes at first video issues, and then intermittent shut offs, and then failure to turn on eventually. The replacement used to cost us about $275 for the part and labor in 2004 - 2005. It was worth it then when the machines had more value.

These days you be better off putting that towards a Mini or something else.

Cheers.