I will be working on a G4 (I think) tower and the user is saying that the white power light is one when he pushes it but no other power seems to go through to the computer or monitor (no chime sound). He already replaced the 3.6 Volt battery on the logic board and also hit the reset button (CUDA).

I haven't worked on these for a long time and have some questions:

1. Can I test the power supply using a 20 pin power supply tester? I did some reading up on this tower and it seems that it will have 24 pins on the main power connector to the board (so 4 extra pins).

2. Are the power supplies the same as the ATX model ones for the PC?

I'm steering towards either the logic board or power supply, but hoping there was some way for me to test it first without shelling out a bunch of money for a part I don't need. Both of these cost over $100 when I just checked out the prices.

Thanks.

I'm not quite sure about a PowerPC based Mac's inner working. However, I don't think a regular PC ATX is the same with the Macs.

I suggest asking the pros at Apple Forums:
http://discussions.apple.com/index.jspa

xboxrulz

Just looked into it more this evening and found that the voltages are different. It might fry the logic board if an ATX power supply is used on the PowerMac.

Well, I took a look at the machine and used the power supply tester (not sure if it's the same reading for Macs) and it showed no signs of power at all. I even unplugged all the unnecessary components inside and the power button light just powers on as long as I keep pushing it. The logic board looks ok, so I guess we'll have to start with the $100 power supply.

If it's the generation I'm thinking of, most have needed new powersupplies after 4-5 years. It can happen, if you keep any computer that long it's one of the componets most likely to go.