Power Mac G5 boot issue

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Level 1

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Power Mac G5 boot issue

Hi all,

I'm having trouble's with my recently aquired Power Mac G5. It's the dual 2.7GHz liquid cooled model, 2GB DDR-400 (4x 512), 2x 160GB drives. It all originally started with a coolant leak which seems to be a pretty common occurance with these models, however I repaired this (which included replacing the power supply unit). The RAM, HDDs and PRAM battery are all brand new.

The unit will power up when you hit the power button (i.e, the fans rev up as normal, the hard drives spin up and you can hear the liquid cooling pump running) but the power LED doesn't stay on. It only illuminates when you actually press the button. There is no boot chime or anything displayed on the monitor. The fans eventually speed up to max speed and you can feel that the CPUs are generating heat. The unit will switch off if you hold down the power button for a few seconds.

The diagnostic LED next to the RAM only illuminates when you remove the air deflector (and HDD bay fan revs up accordingly) and there is no obvious visual damage to the unit. There is a red LED underneath the CPU & cooling unit however, but I haven't found any information about what this one is for.

Any information on this would be greatly appreciated! Thanks

PowerMac, Mac OS X (10.4)

Posted on Aug 29, 2011 8:13 AM

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Answer 1

romko23

Level 2

408 points

Aug 29, 2011 11:12 AM in response to JakeB17

Hi,

Now, you mention that you repaired the liquid cooling, correct? Once you removed the processors or reseated the processors you need to run what is called: Thermal Calibration. Do you have Apple Service Diagnostic 2.5.8 which has the Thermal Calibration program you need? Without the thermal calibration software your fans will rev up to max as the fans' sensors don't know how to cool the processors, hense you need this program.

Once you run thermal calibration, then the fans should run normally and everything should boot up fine. If that is not the case, try an SMU reset.

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Answer 2

JakeB17 Author

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Aug 29, 2011 11:31 AM in response to romko23

Hi and thanks for responding,

Unfortunately the machine wont even boot to the initial grey screen so I can't get it to boot from an optical disc. I did try a PMU reset (as this is an earlier which SMU eventually replaced I believe) but it didn't seem to make any difference. I will try to get a disc though so I can perform the recalibration *if* the unit gives me something to work with. Thanks

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Answer 3

romko23

Level 2

408 points

Aug 29, 2011 11:50 AM in response to JakeB17

Jake,

Sounds like a faulty front panel board. When the front panel board goes, lots of weird things can happen.. for instance, you go to turn on your machine and all you hear is the power supply running, but nothing boots up and no light comes on where you turn on the machine. The more I think about this it sounds like a faulty front panel board. Its not a difficult fix, but finding the part could be hard since Apple now has the Early 2005 G5 power macs listed as "vintage".. Mine which is a late 2005 will be vintage status in early 2012, so I will need to get as many parts for mine as needed.

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Answer 4

JakeB17 Author

Level 1

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Aug 29, 2011 12:12 PM in response to romko23

Hi,

I hadn't thought of that actually. All of the internal fans and drives do power up though, could this still occur even though it might be the front panel board that's failing? (It does seem to be quite flimsy around the area where the connector is.. I can imagine I might have damaged it when first removing the cable)

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Answer 5

JakeB17 Author

Level 1

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Aug 31, 2011 1:26 PM in response to JakeB17

Hi,

Just an update. I removed the front-panel board completely and started the machine by shorting the power button pins on the logic board. Unfortunately there was no difference to the start-up than mentioned originally so we can assume that the front-panel board is working OK.

While I was at it, I also tried a full PRAM/SMU reset by removing power and battery for 20 minutes, reinstalling the battery, pressing PRAM Reset, plugging back in and starting, but was also unsucessful 😟

Jake

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