Powermac G5 failure: logic board or PSU?

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gvim

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A dual 2Ghz Powermac G5 I bought in December 2003 failed to restart in February this year after I replaced the PRAM battery and it hasn't worked since. I've tried all the recommended resets but it won't start so I'm considering replacing either the logic board or the PSU. 'Trouble is I don't know which is faulty. Here are the symptoms:

1. Single click sound near the PSU when the power cable is plugged in.
2. When the power button is pressed:
- a. The power light comes on and stays lit as long as the power button remains pressed
- b. The 2 CPU fans are momentarily jolted, along with a single click sound so some power seems to be transmitted
3. Nothing else starts
4. Same single click sound as 1. when the power cable is unplugged.

The thing is so heavy I can't get it in for a repair as I don't drive so I have to determine categorically which part has failed - PSU or logic board. Any help appreciated.
 
One additional clue to all this is that the G5 had been in continuous daily use for about over 6 years then was left unused for about a month after I successfully built a hackintosh. I then replaced the PRAM battery and it died. Maybe the intervening period of disuse was significant?
 
Here's some things to try:
reseat the graphics card.
If that doesn't help, disconnect your power cord, and remove that PRAM battery. Test it for more than 3.3 volts (an almost new battery does not mean it's good - test it with a voltmeter for at least 3.3 volts. A new battery should be between 3.6 and 3.7 volts.) Put your tested battery back in, and wait 10 seconds. Press the PMU reset button once only (it's not near the battery, but is under the RAM slots near the bottom of the logic board), Do not press a second time, as you may crash the PMU chip.
Wait another 10 seconds, then plug the power cord in. Then try the power button.
If you still get nothing, Try removing the bottom processor. Your PowerMac will run with only one processor, but it must be in the top slot. If it still doesn't start, then try swapping the bottom processor into the top slot.
If you still get nothing, it could be the power supply, but a bad power supply will usually not make any 'clicks' when you plug the power cord in.
After that, it gets to be not worth it to fix, unless you have a complete spare PowerMac for parts.
 
Thanks, DeltaMac for a very informative reply. That's the most in-depth advice I've heard since researching this problem. Will work on it later and get back to you.
 
Not really advice, but I did go almost step-by-step for troubleshooting your problem, directly from Apple's service manual for your PowerMac G5.
 
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