A while ago I obtained a G5 dual 2.7Ghz PowerMac with the intent of installing MorphOS. I currently run MorphOS on a G4 MDD so this would be a nice performance upgrade.

Initially, the G5 would run for about 10-20 minutes; the fans would then speed up and shortly afterwards it would shutdown. It ran like this for a few months. I intended to repaste the cpus and check the cooling system.

Before I could do this a new problem appeared. When attempting to start-up there was sometimes no response when the power button was pressed. Cycling the power supply switch would sometimes cure this new problem. I would then press the power button, the machine would start-up and then operate as described above, shutting down after 10-20 minutes. Pretty soon however, cycling the power supply switch no longer ‘cured’ the problem and when I subsequently pressed the power button instead I would hear a click followed by a second click from the power supply and then – nothing.

As far as troubleshooting, I have replaced the battery and reset the mcu. I have also removed/reseated memory, gfx card, HDs one at a time. My machine has the Panasonic heat exchangers. No leakage evident.

That is where I am at presently. The 2.7Ghz model takes a 600w power supply. I have tried a 450w supply. I was optimistic at first because when I pressed the power button, the machine immediately came to life, the fans came on – but after about 3 seconds it shutdown.

I have 2 questions for our G5 gurus:

1. Should a 450w Powermac power supply work in the 2.7GHz G5 or is it looking specifically for a 600w supply?
2. Any other ideas on troubleshooting or things I could look at?

I think you should consult with the G5 service manuals. They have step by step diagnostics outlined, including voltage measurements and LED states. I'd imagine 450W would work if your graphics card isn't drawing too much.

G5 Manual

[ Edited by jacadcaps 04.04.2021 - 16:58 ]

Thanks. I should have mentioned before that I did follow the troubleshooting in the G5 service manual for the power supply and PMU (I called it the mcu in my initial post).

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Not sure how related my issues in the past is to yours, but I ended up having a bad GPU. I tried everything and nothing would solve this. Someone on a Mac forum recommended I swap out the GPU and it solved all my issues. It was strange.

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Interesting. I will give it a try and see if I can swap it with the G4. Thanks for the idea.

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I'm not quite sure what gfx card you have in your G4, but for Apple Radeons this could be impossible. Wouldn't the "G4 style" ADC power connector interfere with AGP Pro standard G5 slot? Anyway, here's the compatibility chart for the gfx cards.

I wonder why you haven't checked temperature of CPUs and components before system shut-down! I also know such a behaviour, if some components becomes to hot.......(including PSU!)

Use CPUFanControl to check: https://bigfoot.morphos-team.net/test/PowerMac7FanControl

It's also a good advice to check the system with Apples Diagnostic-CD:

https://web.archive.org/web/20170310014624/http://www.dreamsupport.us/downloads/apple-mac/Apple_Service_Diagnostic_Disks_25_GB/ASD%20v%202.5.8%20Dual%20Boot%20CD%20(2005)/

It's worth noting that you cannot be really sure the coolant didn't leak just looking at the CPU modules and not disassembling them. When I visually checked my G5 2,7 GHz CPU modules they looked OK, but the overal state of LCS turned out to be very poor. Look here:

The water block developed significant white-greenish residue around itself (O-rings leaking):

o8YecD9.png

The tubing got almost completely clogged by aformentioned residue:

3Jk9TI2.png

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Yes, I used CPUFanControl to check cpu temps until the machine stopped running. I didn't mention that in my initial post. Temps were around 85C. That is why I said that I was planning to repaste the cpus, although from my research it does appear that G5s run quite hot. What would a 'normal' temperature range be for a G5?

Thanks for the link for the Apples Diagnostic-CD. TRhat will come in handy.

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Good call. I had both machines apart yesterday. Yup, slots are quite different. ATI Radeon 9000 Pro in the G4 and Radeon 9600 in the G5. Too bad. There goes that idea.

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Yikes. I will add this to my worklist. thanks.

I think 85° is very high (but I don't have a liquid cooled Mac). My G5/2.3GHz (aircooled) is running at max.70° under MacOS - which is very high too, in my opinion. Under MOS I've defined it to max. 65° (which does'nt give loud fans during normal work) and backsidetemp is also limited to 55° by CPUFanControl.. (many G5 died in reason of too high backsidetemperature)

[ Editiert durch Amigaharry2 11.04.2021 - 19:15 ]