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The PowerMac G5 is a desktop computer first produced in 2003 by the Apple Corporation. This guide will review the repair process of an Apple PowerMac G5 model number A1047 EMC 2061 from 2004. It was discontinued in 2006 as part of the Intel switch first to developers then consumers.

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Power Mac G5 won't start

Late 2005 Power Mac G5 (Model A1047) does not power up. It fires up, the power button light on the monitor blinks (single blinks about every 4 seconds) but the monitor does not light up. The fan in the tower does start running after its on for sometime, but no display or anything else. Tried the cudo (?) button (for one second first and again for 30 seconds as suggested on a forum), and resetting the PRAM (command+option+P+R), force shutdown..... nothing works. I have 4x 1 GB RAM installed and they are paired.

This is a hand down computer that has been sitting idle for months (maybe even a year) now. Not sure if that is the issue. Any help is appreciated.


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YellowStickie, see if this helps to narrow it down a bit. I am not a Mac person, just a hardware tinkerer with a few manuals ;-). Hopefully this will keep you busy until the Mac Guru's get to your question :)

" Power-On Self Test: RAM and Processor Verification

A power-on self test in the computer’s ROM automatically runs whenever the computer is started up after being fully shut down (the test does not run if the computer is only restarted). If the test

detects a problem, the status LED located above the power button on the front of the computer will flash in the following ways*:

1 Flash: No RAM is installed or detected.

2 Flashes: Incompatible RAM types are installed or RAM installed in wrong slots.

3 Flashes: No RAM banks passed memory testing.

4 Flashes: No good boot images are detected in the boot ROM (and/or there is a bad sys config block).

5 Flashes: The processor is not usable.

  • Note: The status LED lights up when the power button is depressed at startup. Do not count this light as one of the diagnostic flashes.

Diagnostic LEDs

Power Mac G5 (Late 2005) logic boards include a set of LEDs to help service providers troubleshoot the computers. The LEDs are located to the left of the top bank of DIMM slots.

Block Image

Power-on LED illuminates when power button is pressed and fans spin continuously but there is no boot tone or video

Reseat video card. (Make sure video card is fully inserted in connector and end of card is secured by the connector latch.) For video cards that require power cables, check that they are connected.

Verify speaker cable is fully seated.

Reset logic board. Refer to “Resetting the Logic Board” in this chapter.

Check diagnostic LED 1 and LED 6 for processor connection

Replace processor

Replace logic board

Power-on LED illuminates when power button is pressed, fans spin, and boot tone chimes, but there is no video

Reseat video card. (Make sure video card is fully inserted in connector and end of card is secured by the connector latch.) For NVIDIA Quadro FX 4500 graphics card, check that power cord for card is connected.

Reset PRAM (restart computer while holding down Command-Option-P-R keys until second boot tone chimes)

Reset logic board. Refer to “Resetting the Logic Board” in this chapter.

Replace video card

Replace logic board

I posted a service manual to the device page. Check on here under Support documents. Have to tell you I love the looks of the G5, my kind of machine :-)Hope this helps, good luck.

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The power supply is not mentioned. My fan does not go on (though for a long time, when it was working, I could not manually put it to sleep or the fan would rev up and race loudly, and cutting the power was the only thing that worked. I’ve reset the PRAM, replaced the PRAM battery (a flat nickel-shaped one, not the usual short AA type)

My question is how to know whether its failure to boot is due to a faulty power supply or bad system board.


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Thanks for the email. First thing I would do is replace the 3.6 volt 1/2 AA PRAM battery

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Did your mac G5 work now? I also have the same problem.


will check the battery. Has 8G ram just noticed it now indicates only 4G ram!!! thanks


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Late 2005 eh? Sitting for months to a year eh? I'm sorry to say, you might have a leaking cooling system. The late 2005 2.5 and 2.7 eventually start leaking due to failure of the liquid cooling system for the CPUs. Sitting for a long time like you said makes be think the cooling failed

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late 2005 2.3 dual no liquid cooling , but have just noticed loss of 4Gig of ram thanks


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I had the Power-On-Click/Power-Off-Problem. Most forums told "it was dead".. (bad soldering contacts, powersupply etc.) ..IT WORKS NOW:

The solution is to make maimboard-reset WHILE POWERCABLE PLUGGED!! Remove onboard-battery first. The manual shows the motherboard-reset with working battery! While the mac is plugged to power you don't need any battery - worst case is lost of date and time settings.

I don't know any electronic device that does anything WITHOUT POWER :-)

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