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Two more things to test:

1) Bad RAM? Try removing the DIMMS and reinstall them one at a time to find ones that are bad.

2) Bad Power Supply? This is hard to test unless you happen to have another good one around.

Try resetting the CUDA switch.  Its a small round button on the motherboard.  I can't remember exactly where it is (I think near the RAM slots) but if you press that button, it will reset the motherboard.  Mine did a similar thing after I added RAM one time.  Took care of the problem.  Just push it once, count to ten and then try booting again.

I tried unplugging everything, and I've tried resetting the mother board several times. Still nothing. If I take it to the genius bar at my local apple store will they be able to tell me if its the power supply or the board?

Damn, first mac to ever die on me.

Do they have the parts available to fix it there? I'm sure a new logic board is $$$

http://resale.headgap.com/bobsmactips.html

If you want to dig deeper, this place has some relevant tech tips. It's a long page though. About 2/3s of the page down you'll find:

"Help! I pushed the CUDA Switch on my G3 or G4 and it still is not working

LET ME REPEAT: BEFORE YOU GET TO THIS POINT, you may want to ask yourself what happened just before the computer quit working. Perhaps taking out that new stick of ram or that new PCI card will get your system working before going to extreme measures. Even items that were working okay but recently installed may be suspect. Sometimes things fail. Try taking them out first.

Sometimes computers lose their mind. Don't ask me why or how it happens but it does. Sometimes you simply have to totally discharge the computer. One thing I have learned about the Blue and White G3 and G4 computers is that sometimes pushing the CUDA is not enough. If your machine still is dead, then try the following.

    * Unplug the Unit
    * Remove the Battery
    * Push the CUDA Switch (count to 5 slow)
    * Push the Start button on the front of the computer (count to 5 slow)
    * Let the unit sit for 15-30 minutes
    * Replace the Battery
    * Plug it back in, and push the start button

Amazing! It works again!! If it doesn't I usually repeat the steps above, pull the ram, and let it sit overnight. Make sure you only have the keyboard, mouse and monitor plugged in. I usually also remove PCI cards and leave only one stick of ram. If it doesn't work after this it is take it to the shop time (or ship it to us)."

Last edited by adamjg (2007-11-03 2:22 pm)

Sounds like the logic board if you ask me, i had a sawtooth do the same thing once. I just got rid of it since they wanted an arm and a leg for the logic board

FYI, I've revived seeming dead computers (G3s) by unplugging all the major components (and batteries), letting sit for a day or more, pressing all the reset and CUDA buttons, and carefully putting all the stuff back in (and trying alternate RAM and Drives too).

Sometimes that works, sometimes not!

Last edited by adamjg (2007-11-03 4:27 pm)

Just picked up a QS dual 800 for $137. So I'll be parting out the 733 and selling off the stuff that still works, along with the dual 800 CPU since I have a gigadesigns CPU upgrade on the way. Thanks for the help everyone.

Hi group,
I have a M8493 QS G4 tower with the symptoms of: was working fine in the AM, walked away, came back and Mac was off.  I pressed the power button & it lit white while I held it, went out when released.  I found this site surfing for help.  I followed adamjg's advice:

Sometimes computers lose their mind. Don't ask me why or how it happens but it does. Sometimes you simply have to totally discharge the computer. One thing I have learned about the Blue and White G3 and G4 computers is that sometimes pushing the CUDA is not enough. If your machine still is dead, then try the following.

    * Unplug the Unit
    * Remove the Battery
    * Push the CUDA Switch (count to 5 slow)
    * Push the Start button on the front of the computer (count to 5 slow)
    * Let the unit sit for 15-30 minutes
    * Replace the Battery
    * Plug it back in, and push the start button
IT WORKED!! And now my QS lives again.  adamjg THANK YOU so much!! 

I guess I found the CUDA switch right next to the 3.6v 1/2AA tl-2150 battery holder.  Thanks Again!!