Two Quad-Questions

Discussion in 'PowerPC Macs' started by fuzzface, Mar 20, 2015.

  1. fuzzface macrumors newbie

    Apr 1, 2011
    Hi folks,

    for some months I bekame more and more annoyed with the noise from the gpu-fan of the 7800gt in my lovely G5 Quad. Googling resulted that this is a common problem with this card, probably due to a failing transistor.
    Anyhow, I looked out for replacement-fans and came across the Arctic Cooling NV5 Silencer. Since these fans are not easy to get these days (there was one on ebay for about 30 Euros, including shipping, which seemed a OK-price but too expensive in second thought), I choosed simply to wait.
    A week ago there was a Quad on ebay Classifieds (since Craigslist is not really an option here in Germany). The unit was advertised as "would not boot". But it got a nice genuine FX4500 inside, so the 60 Euros were almost a non-brainer.
    I put the Card in my Quad and it's running fine and is much more silent than the 7800gt. Im very satisfied. So long, so good.

    Since I'm on vacation these days, I became interested in what was wrong with the broken Quad.
    The machine would power on, solid white Light, fans spinning, HDD comes up, no diagnostic-LEDs, but also - no chime. I noticed, that the fans would not turn into hurricane-mode after some time and long-pressing the power-button would do nothing. I had to unplug the cord to switch the unit off.
    So I pulled the processor-block (2-pump-version from Cooligy), repasted and switched the CPU-cards - same results. Next I tried with only one processor-card in the upper position installed. No go. After swapping cards again (bad luck), the machine would chime and is running fine since, with low temperatures and idling fans.
    One Diagnostic-LED (No. 6 - reseat CPU B) stays on permanently, though. That's OK, since there is no 2nd CPU-Card installed.
    So it seems to me like the lower processor-card is toast, probably due to a failing LCS. I know the Cooligy-System has two independent cooling-cycles, so the LCS definitly needs service.

    What brings me to my first question:

    What would You do?
    Sell for parts, archive the machine for replacement or refurbish?

    If I decide to restore the machine, I need a new CPU-card.
    Servicing the LCS (which, thanks to Heikki Lindholm's excellent writeup, I already have done on my first Quad with the 1-pump-version from Delphi) is another story, but not deterring. For me it was kind of fun working on it, but took some time and expenses...
    So restoring the LCS would also mean further costs.

    The defective CPU-Card brings me to my second question:

    The Apple-part-number stamped on the card is 820-1792-A. Since I found out that the heatsink-fin is detachable (after a rude loosening with a flathead-screwdriver - very sticky thermal-pad), the CPU-cards seem to be interchangable between the two LCS-variants. So it must be possible to aquire a "new" CPU-Card.
    A little search on google brought me across some US-auctions on ebay. One Seller is advertising a 2-GHz-Card which has the same part-number. Further digging unveiled that all Late-2005-processor-cards (I found at least some 2GHz- and 2.5Ghz-ones) seem to share the same part-number.
    Could that be?
    If this is true, the hard-coded frontside-bus-speed of the logic-board (1GHz for the 2GHz, 1.15 GHz for the 2.3GHz and 1.25GHz for the Quad) seems to determine the CPU-clock-speed.
    Can this be true?

    It would be interesting if some of You know more about this finding.
    Also I would appreciate your opinions about what to do with the machine.

    Cheers and thanks for reading for so long,


    P.S.: Here're two photos of the CPU-card in question.

    Attached Files:

  2. Altemose macrumors G3


    Mar 26, 2013
    Elkton, Maryland
    I would rebuild the machine and install a new CPU card and overhaul the LCS. There are a number of members here with parts on the Marketplace, and there was a thread by a member looking for a quad where parts were offered. Perhaps you could PM them.

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