11 Replies Latest reply: Jul 30, 2013 7:08 AM by mikiotty
mikiotty Level 1 Level 1 (0 points)

Hello everyone!

I recently bought a second-hand PowerMac G5 Dual 2.0GHz June 2004 model. The guy that sold it to me said he was selling it because of a power supply issue. He told me that an Apple Genius noticed a PSU failure and that a PSU replacement would cost him about 350€ (I'm in Italy), so he decided to sell the computer. Meanwhile he bought a replacement PSU from an eBay shop. When I first plugged in the Mac (with the original PSU), there were no life signs. I thought that was a real PSU problem and I decided to test the new PSU before putting it into the computer. I connected the PSU to the power and... it literally exploded. Lucky I didn't put that PSU into my G5.

Anyway, I'm in the same situation as before. When I first tried to plug in the computer, I noticed a very short blink from the power LED. However, the computer won't start at all. No fan noise, no lights, nothing. I then tried to reseat RAM, video card, fans... nothing. I then tried to replace the PRAM battery and resetting the PMU, same results. I decided to reseat the processors being extremely carefully, but nothing. At this point, I decided to test the original PSU on the bench and it seems to be outputting all the correct values (all the 5V, 3.3V, 12V, -12V, 25V) on the correct pins, even under a small charge. I then tried connecting pins 14-23 and the PSU fan started running. I then tried to manually give the OK for the voltage to come up on the logic board by connecting those pins with the PSU plugged into the logic board. All the fans started running very slowly, but that's it. Nothing else happened (Note: I tried this without RAM, CPUs, video card etc. I then read that this model won't start without even one CPU, they both have to be on the logic board, that's probably because it didn't proceed with the boot sequence).

Any idea? I don't want to spend 950€ on a new logic board, and I may try to repair the components on the logic board myself if it's necessary (I have a lot of experience in soldering etc, I already replaced 6 caps on an iMac G5 logic board and now it works perfectly). Anyway, reading on the web, I think I have a bad switch on the front board (the one with the power button). The button itself works, maybe the circuitry on the board died. I'm not going to buy any component before I'll find out what the exact problem is BTW.

 

I rely on your help! Thank you (sorry for my english)!


PowerMac
  • 1. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    BDAqua Level 10 Level 10 (116,465 points)

    I think it does need at least one CPU, CPU0, it may start without CPU1.

     

    PS. Your English needs no apology, quite good in fact!

  • 2. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    Thank you :) anyway, living out the processors, what do you think about my problem? What could be the problem in your opinion?

  • 3. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    BDAqua Level 10 Level 10 (116,465 points)

    It certainly could be that little board behind the power button.

     

    Here's some more info on G5 PSU voltage values:

     

    http://www.insanelymac.com/forum/lofiversion/index.php/t105113.html

  • 4. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    I found some very detailed informations about testing the PSU, but I couldn't find detailed informations about this simple thing: a working G5 PSU, how many relay clicks does when I plug in the power cord? And how many when disconnecting the power cord?

  • 5. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    Good news! I managed to start the Mac only one time (with no PRAM battery, no intake fans, no video card, no optical drive... only with 2 processors, the RAM and the exhaust fans). It gave me a lovely bong and both the exhaust fan started running fine. Then I turned it off and unplugged it from the wall to insert all the other components and it doesn't want to start again.

    At this point, it could really be a bad PSU (evet if it works perfectly on the bench, apart from a double value on a resistance). I've got an iMac G4 that has about the same problem (it won't start unless you unplug it and plug it back to the power for a few times). What do you think? Let me know, if you think that it's a PSU issue I'll try to buy another one. Thank you!

  • 6. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    BDAqua Level 10 Level 10 (116,465 points)

    On the iMac G4 I'd say it's a bad capacitor that needs to bleed down. On the G5, try adding one component at a time between the minimal way it started & up, I suspect maybe Video card, but...

  • 7. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    I already checked all the caps on the iMac G4 and they are all OK.

    The G5 didn't start anymore after that single power up, neither in the "working" conditions. Video card seems to be fine, I tried another card (FX5200) from another G5, same results.

    There is something on the PSU or the logic board that stops the Mac from powering on (I also noticed that one of the pins of the air baffle sensor/HDD bay sensor cable is cut, I'll fix it this Monday when I can work on the Mac again), but I can't figure out exactly what. Very, very frustrating!

  • 8. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    BDAqua Level 10 Level 10 (116,465 points)

    On the G5 anyway, the little board behind the power button may do this.

  • 9. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    Ok, I should have another compatible front board to test with my G5. I'll try on Monday Thank you

  • 10. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    Ok, big update.

    I used my G5 all day today and it works just fine. The problem was (is) on the upper processor (since this model doesn't start without both processors in place, even swapping them putting the working one on the top), and I think it's a bad contact between the processor and the logic board or either on the processor board.

    This morning I removed the upper processor and noticed that the heatsink pipe just under the board was bended. I put that **** thing back in the correct position and reseated the processor. I immediately noticed that the two processors were correctly aligned (before bending the pipe, the upper processor was noticeably relieved on the right side and out of line with the other one). I tried to boot the computer and, with a very light pressure on the right side of the processor, the Mac started with a lovely loud bong.

    I then ran all the tests on the Apple Service Diagnostic disc (excluding the PCI ATI Video Controller, known bug on that model with ASD 2.5.8) and all the test were fine.

    Rebooted the Mac, installed OSX Tiger (didn't have a Leopard disc at the moment), all fine. Booted into Mac OS X, updated to 10.4.11, all fine. Installed iStat Pro widget and noticed that the temperature sensor on the CPU0 (yes, that same **** CPU) didn't work. Reboot again in ASD, re-run all the tests: "CPU0 thermal sensor reads under alarm setting 3". It was reading 9°C. Tried to run Thermal Calibration, same problem on CPU0, ok on CPU1.

    Apart from this problem (that prevents the CPU fan to ramp up, but it isn't a big deal: I can set the fan to run always at full speed or at least add another intake fan on the front of the computer, even a simple PC fan), the Mac works really well.

    After 3/4 hours being on, it started to boot even without touching the CPU. I think expansion due to heat makes that **** thing to work.

    I could try to fix the thermal sensor, I'll decide later.

  • 11. Re: PowerMac G5 Dual 2.0GHz June 2004 seems dead... how do I fix it?
    mikiotty Level 1 Level 1 (0 points)

    Another update.

    I'm writing from the G5 at the moment, and it seems to have some CPU-related problems. Apparently, that CPU is going to computer heaven... when I export any kind of video (ScreenFlow recordings etc) I have serious glitching on the final product and on the display during the exporting process (but not watching the recording on ScreenFlow itself).

    The positive note is that the computer now starts pretty much all times (sometimes it even starts without touching the CPU) and goes to sleep. In any case though, even when I wake it from sleep, is necessary to move the CPU (that glitching could be caused by a damaged contact on the processor board, as I said yesterday, and when I move the CPU the Mac has the OK signal to start up, even if the processor isn't actually in place after the boot sequence start).

    The thermal sensor on that CPU isn't working, so I screwed a normal 120mm PC fan and connected them to the Optical Drive Molex connection with a proper converter. It's a bit loud, but I think it's enough for the processor to stay cool.

    At this point, i'll probably replace that CPU with a new one when I find money and time (and a good offer on eBay or something like that).

    I'll try to use my G5 monitoring the CPU temperature with my hand, but it's summer here and it could get very hot indeed. We'll see.

     

    Thank you for all the support!