How to test a G5 power supply

[iTris]

My 2*1.8Mhz G5 tower (second version) shutdown two day ago and refuses to turn up again. I have absolutely no sign of life, not even the external white led or the internal red one. I'm trying to figure out whether it is the power supply of the start button which cause the problem.

Is it possible to test a G5 power supply like an ATX power supply, by connecting two pins which would make the fans start ?

[MClever]

To test a G5 PS, you must measure for a trickle voltage on Pin1 . There will be+5Vdc (btwn Pin1 & Pin 23 GND) after plugging in the AC Cord. If there is no trickle , the supply is bad.

(Note: Pin 12 and 24 are empty. Pin 13 is GND. These are the other 4 corners. You probably will have to remove the black cover to expose the wires).

Pin 14 is PWRON. I've never jumpered that to ground to force a power up, but that is the only signal listed that is similiar to the ATX signal used to force a power on.

I doubt that the front panel board is bad, but there is always a first time.
I've seen a failed processor not allow a PM G5 to power on, so nothing in these units surprise me anymore. (You can run 1 processor at a time, but return them to their original slot. Otherwise the thermal calibration will be off and the fans will run fast all th time).

Good luck!

[iTris]

Thanks a lot for your very complete answer. I tested the pins as you advised and got nothing so it is effectively a PSU problem.

Thanks again

Tristan

[iTris]

I changed the power supply today. The mac now turns on, every fans work correctly but I have no display. I checked with 2 video cards with the same result. I also look like the powermac refuses to power the old usb apple keyboard I have. caps lock is not active. a usb mighty mouse do light up however. After a few times the fans turn to hurricane mode. I'm starting to be desperate about having this machine work again.

If someone has an idea, or a another test I could do, I'm all ears.

Thanks

Tristan

[MClever]

Reseat the processors. Many times they feel like they are the whole way back in, but are not. It would not hurt to check the pins for the CPU socket on the logic board. I've seen 'em bent over by improper installation (which is extremely easy to do). Since you stated earlier this is the 2nd Gen G5, running 1 CPU at a time might not work for you. The earlier models could run with just one CPU installed. As I recall, the top slot had to be occupied.

It is normal for the fans to kick into high gear if no video is present (in failing mode). However, once you get video and it still is there, you might have accidentally switch the processors. Shutdown and switch 'em back .

[iTris]

Thanks a lot again, you were right, the processors where not reseated correctly. Everything works fine again now.

[gtarantola]

Hey guys. i know this thread is 3 years old, but i'm having the exact same problems with my G5 June 2004. I have metered pins 1 to 13 and pins 1 to 23, and get just over +5VDC on both. i have also metered across pins 1 and 2 and measured around 7KOhm, as suggested in this thread: http://discussions.info.apple.com/me...ageID=11980210

i have tried different PMU battery as well. if i hold the pmu reset while plugging the power in, the front panel light will stay lit as long as i hold the button. any ideas?

[DeltaMac]

You didn't say which processor you have. If it's a dual 1.8 GHz, then you can try removing the lower processor, and see if your G5 will continue to boot. You can't do that with a dual 2.0 Ghz or higher, unless it's a first generation.
Do the fans spin up at all, and do you get a boot chime? Each symptom (power light, fans, boot chime, video) will take you to a different troubleshooting step.