G4 800 tower switches off after start-up

M

multidiscipline

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I have a G4 800 powermac Quicksilver tower. I haven't used it regularly for a number of years, although it has been started up say every 5 months or so without any problems at all.

Last weekend I started it up and it worked for about 2 minutes before suddenly shutting down, without warning. I tried starting up again and it started up, only to shut down as soon as the desktop appeared.

I started up again, and whilst the light in the power switch on the front panel illuminated, and a short 'apple boing' noise came on, it just shut down immediately after.

Having left the computer untouched until the following weekend (today) the same order of events has unfolded. two minutes for the first go until unannounced shutdown, and then progressively shorter amounts of power.

Whilst this isn't a critical piece of hardware for me, it does hold some useful data, can anyone help me to resolve what the problem might arise from, and hopefully suggest a way to fix it. I have no idea if this problem is hardware or software related.

Looking forward to hearing your thoughts.
 
Quite sure that'll fix you up, however, if not; 1 last fix: reset the PMU--a small black button on your motherboard (make sure the Mac is off before doing so)
 
I've got the battery now, but will have to wait until the weekend until getting back home to fix the computer, I'll let you know how I fare then...
 
I seem to have a problem with the same symptoms. G4 starts, runs anywhere between a few seconds to a minute or so, then suddenly turns itself off. I replaced the battery, did PMU reset, started with all peripherals disconnected, including internal hd and cd-drive, started without memory, without pci cards, including taking out the video card. Always the same: after a short moment the power goes off. The exception was when there was no memory: computer beeped and kept blinking the power light but stayed on. Once I got lucky and it was on long enough to get thru the login screen to the desktop.

Sounds like either the motherboard issue or power supply. Is there a simple way to figure out which it is? I actually have another identical G4, so I could take the power supply from and try it out. But that requires some effort.
 
multidiscipline said:
I've got the battery now, but will have to wait until the weekend until getting back home to fix the computer, I'll let you know how I fare then...
Click to expand...

I bought a new battery, inserted it, also reset the PMU whilst the side of the tower was open. Curiously it's even worse, when the start switch is pressed the switch lights up, but the computer doesn't start, not even a whimper.

Strange that changing the battery should make it worse... any further thoughts?
 
I'm hoping that when you put in the battery, that you did it with the power off and the Mac unplugged.

The procedure is the following:
  1. Turn off and unplug the computer (regardless if it's a Mac or not, this must be done when working on the inside of any computer).
  2. Open up the Mac.
  3. Replace the PRAM battery.
  4. Push the PMU reset button that's near the battery ONCE AND ONLY ONCE (holding down the button for too long or more than once can crash the PMU, causing the battery to degrade).
  5. Close everything up and plug in the power cord.
  6. Turn on the Mac.
 
I certainly unplugged the unit before opening it up (don't like the idea of frying myself when opening up such a machine, or any machine in fact), but I did push the PMU button a number of times, holding it down for a few seconds at a time, oh man, does this really mean that the otherwise new battery is completely done for?! There goes 12 UK pounds worth of battery, what a waste. That would explain why nothing happened when I did plug it back in then wouldn't it. Seems daft that this little battery could be so easily killed. I'll need to reinvest again in a new battery won't I. Now that the PMU button has received it's fair share of pushing, do I need to do it again when I put another new battery in?
 
Well, it won't kill the battery, but it can degrade the life of it. It only needs to be pushed once.

Also, make sure that you leave it plugged in for a while before you actually turn it on. Sometimes, it seems that leaving it alone for a while after the battery has been replaced will help. Happened to me with an old LC II and an old StarMax 4000 Mac clone after I changed the PRAM battery on them as well.
 
Sounds like either the motherboard issue or power supply.
Click to expand...

OK. It took some effort to swap the power supplies but now it is confirmed that the power supply is the source of the problem.
 
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