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tobyjah Level 1 Level 1

I have a Power Mac G5 (June 2004). Recently when turning on the plug switch (at the wall) there was a power surge to the Mac which blew the internal power supply. I bought a reconditioned PSU and replaced the blown one (following online instructions). When I turned it on again, it booted up, but without the start up chime and a blank monitor screen. The monitor power light is on, but nothing appears on screen (black). Eventually the fans go crazy and only stop if I turn the Mac off. I can't boot up in safe mode as there is no chime and have tried command shift P R to no avail. After much searching I'm lost as to what to do next.


Anybody have any ideas?

  • BDAqua Level 10 Level 10



    Might be time to replace the PRAM Battery, 4 years is close to their lifespan, far less if ever without AC power, & can cause strange startup problems...


    See which one your G5 has...




    Have you done a PRAM reset, CMD+Option+p+r...



    In fact, do 3 in a row, takes a bit of time.


    How to reset the SMU/PMU on a Power Mac G5 (Late 2004) or Power Mac G5 (Late 2005) ...



    Earlier G3, G4, G5 models...



  • branddoc Level 1 Level 1

    Guys, I have the same problem but not managing to fix it. any additional thoughts. Here is more detail.


    Apple G5 not starting black screen. No chimes. After a few minutes the fan kicks in running very loud. Have to unplug to stop the fan. Have tried apple/option/r then powering on and pressing p. Same result.


    I then replaced the PRAM battery and bingo it worked. Now a few weeks later the same problem occurred. This time replacing the battery had no effect.


    I reset the SMU, but pushing the SMU reset button, but no go.


    I cannot reset the PRAM (from online instructions) because the screen is black and there are no chimes.

  • Jacumba Level 4 Level 4

    When you turn on the computer now it has a black screen, but are the fans running normal, and are you able to turn it off and on with the power button?

  • japamac Level 7 Level 7

    When a major overhaul has failed to produce the desired result, pulling it apart and reinstalling everything is usually a good idea.

    At a minimum, I would reseat the processors, RAM, all cables, PCI cards and graphics card.

  • branddoc Level 1 Level 1

    When i turn it on I can hear themm machibne whirring. i assume this is the fan. and yes I can turn off the machine by depressing the power button for 5 seconds. Does this mean anything??? Can I be saved?

  • branddoc Level 1 Level 1

    That is the doom and gloom answer I was fearing. It is a old work machine so I so not have the system disks or original software.

  • Jacumba Level 4 Level 4

    The reason I asked you if the fans were running was to determine if the power supply was bad, if they weren't that could have been an indication it was. It appears they are but you should have opened the case to be sure and while doing so check if they are clogged with dust.


    I'd like you to try something. Take the ram out of the computer and start it with no ram. Then turn it off. Then put in one ram stick only and turn the computer on. If it starts and you get a screen turn it off and put back in the rest of the ram. I have an older Mac that I have to do this with if it sits for weeks. If I use it regularly it just starts. This is commonly done with computers that are having a problem and alot of times it works, ram gets corrupted or not recognized for some reason or another, so give it a try. I realize that the computer documentation may require ran in pairs, but try to start up with one only.


    Also are you sure the monitor is good? Do you have another you can try with the computer?

  • branddoc Level 1 Level 1

    Hi and thanks for the detailed reply.


    The fan is working, I have checked. I also hooked up a different monitor as suggested.


    I took out the RAM as suggested and restarted and started the machine. No chimes and the fan kicked in running very loud as before.


    I put the ram back in (one stick top slot and matching stick bottom.) and restarted. After a few secs there were two high pitch beeps and the fan kicked in running very loud. I then realized that in fact I had forgotten to put the fan mechanism back in! So what was making the fast running fan sound?

    I put the fan mechanism back in, put all the RAM in and restarted. The same result: two loud beeps and the fan kicks in.


    Losing the will to live now.

  • branddoc Level 1 Level 1

    Oh another thing. Power light flashing.

  • branddoc Level 1 Level 1

    Hi Jacumba,


    I have checked the led lights on the logic board to see if they give any more info for diagnosis.



    Red light top right.

    Red light middle left (third led down),

    Orange light middle left (fourth led down).


    At the bottom of the board there is a green (SYS) led flashing in sync with the power light which flashes two times, repeating.


    When I switch off two lights remain on

    Red light top right.

    Orange light middle left (fourth led down).

  • Sergio Lis Level 1 Level 1

    I do not speak English, sorry if I do not write correctly ... I had exactly the same problem and I could solve it by changing the Lithium Battery 3.6 volts (note that the positive terminal of the battery must be toward the back side of computer) and completely disassembling the entire computer, including the Power Supply, cleaning and removing dust, first with a brush and then with a toothbrush around the Mother Board, cores and fans. Using a vacuum cleaner all the time to remove all the dirt ... After that the Mac started ... I hope it help

  • johnston133 Level 1 Level 1

    Hi Guys,


    This is of course an old post however after remembering my old Power Mac G5 June 2004 sat in attic i fished it out.


    Similar issue... Turned on and had 2 flashing power lights, changed RAM to DDR3200, job done.


    However i now power on and have solid power light and chime, however no display... its a working monitor on DVI (this machine has 1 - longer DVI type and 2 -  normal sized DVI, im using 2 -  normal DVI) and after leaving it on for a 5 minutes the fans get louder and louder until its about to take off. Nothing on screen ... The HDD is being read after chime for very small amount of time.


    machine has not been turned on in years so i will try the above and give it a go (PRAM and check battery voltage / replace)

  • BDAqua Level 10 Level 10

    machine has not been turned on in years so i will try the above and give it a go (PRAM and check battery voltage / replace)

    Good thing to try!

  • johnston133 Level 1 Level 1



    So after hours of effort last night after finding my G5  with solid power lights, chime and HDD activity but no display then extreme loud fans after 5 minutes or so, I have fixed it.


    My June 2004 model has under the RAM slot left to heat sinks a PMU reset button. So I disconnected mains lead left it out for 2 minutes, power on same thing. Powered off keeping mains lead connected I pushed the PMU reset button for 1 second, same fault. Powered off keeping mains lead connected, held PMU reset button for 30 seconds and then powered on, no difference. Powered off, disconnected mains lead, left for 30 seconds, removed and checked PRAM battery and was showing as it should, 3.6v. I kept the mains lead and battery out for 30 seconds or so then connected mains lead back with battery STILL REMOVED, powered on and boom it came alive. Powered down and reinserted PRAM battery and now things are looking good and all is working!


    Whole time I always put the plastic inner cover back keeping the RED light OFF and FANs at a minimum and ESD precautious.


    Be sure RAM is not faulty, if you got dual CPU then make sure they are paired and exact, start with 1 x DIMM in both number (1) banks and are DDR3200 as lower speeds are not supported (on mine anyway)

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