Friday, July 30, 2021

And now for something completely different: "Upgrading" your Quad G5 LCS

One of the most consistently popular old posts on this blog is our discussion on long-life computing and how to extend the working, arguably even useful, life of your Power Mac. However, what I think gives it particular continued traction is it has a section on how to swap out the liquid cooling system of the Quad G5, obviously the most powerful Power Macintosh ever made and one of the only two G5 systems I believe worth using (the other being the dual-processor 2.3GHz, as it is aircooled). LCSes are finicky beasts under the best of conditions and certain liquid-cooled models of the G5 line have notoriously bad reputations for leakage. My parents' dual 2.5GHz, for example, succumbed to a leak and it ended up being a rather ugly postmortem.

The Quad G5 is one of the better ones in this regard and most of the ones that would have suffered early deaths already have, but it still requires service due to evaporative losses and sediment, and any Quad on its original processors is by now almost certainly a windtunnel under load. An ailing LCS, even an intact one, runs the real risk of an unexpected shutdown if the CPU it can no longer cool effectively ends up exceeding its internal thermal limits; you'll see a red OVERTEMP light illuminate on the logic board when this is imminent, followed by a CHECKSTOP. Like an automotive radiator it is possible to open the LCS up and flush the coolant (and potentially service the pumps), but this is not a trivial process. Additionally, those instructions are for the single-pump Delphi version 1 assembly, which is the more reliable of the two; the less reliable double-pump Cooligy version 2 assemblies are even harder to work on.

Unfortunately our current employment situation requires I downsize, so I've been starting on consolidating or finding homes for excess spare systems. I had several spare Quad G5 systems in storage in various states, all version 2 Cooligy LCSes, but the only LCS assemblies I have in stock (and the LCS in my original Quad G5) are version 1. These LCSes were bought Apple Certified Refurbished, so they were known to be in good condition and ready to go; as the spare Quads were all on their original marginal LCSes and processors, I figured I would simply "upgrade" the best-condition v2 G5 with a v1 assembly. The G5 service manual doesn't say anything about this, though it has nothing in it indicating that they aren't interchangeable, or that they need different logic boards or ROMs, and now having done it I can attest that it "just works." So here's a few things to watch out for.

Both the v1 and the v2 assemblies have multiple sets of screws: four "captive" (not really) float plate screws, six processor mount screws, four terminal assembly screws (all of which require a 3mm flathead hex driver), and four captive ballheads (4mm ballhead hex). Here's the v1, again:

And here's the v2. Compare and contrast.
The float plate screws differ between the two versions, and despite the manual calling them "captive" can be inadvertently removed. If your replacement v1 doesn't have float plate screws in it, as mine didn't, the system will not boot unless they are installed (along with the terminal assembly screws, which are integral portions of the CPU power connections). I had to steal them from a dead G5 core module that I fortunately happen to have kept.

Once installed, the grey inlet frame used in the v2 doesn't grip the v1:

The frame is not a necessary part. You can leave it out as the front fan module and clear deflector are sufficient to direct airflow. However, if you have a spare v1 inlet frame, you can install that; the mounting is the same.

The fan and pump connector cable is also the same between v1 and v2, though you may need to move the cable around a bit to get the halves to connect if it was in a wacky location.

Now run thermal calibration, and enjoy your renewed Apple PowerPC tank.

15 comments:

  1. Hi! I've got an iMac G5 20" Model A1145 (iSight) which symptoms look as you describe (the fans never ramp up, then occurs an abrupt shutdown above a certain temperature).
    As I've been using it exclusively as a high-level alarm clock for years now, I'm a bit reluctant to disassemble that compact beast... ;-)
    I sometimes have opened it a few times though (last time was to replace the power supply) and there's no obvious sign of leakage, from what I was able to see.

    Do you think a change of thermal paste could be enough? (if I ever have the courage to disassemble it...)

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    1. iMac G5s are all air-cooled, so it's possible cleaning out and replacing the thermal paste might be sufficient. But you point out the worst thing about the iMac G5: they are a pain to work on.

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    2. I'm surprised: aren't those copper tubes carrying fluid?
      https://guide-images.cdn.ifixit.com/igi/Qfp1MOBfgUNsecKL.huge
      If it's just a piece of metal carrying heat to another point in the computer, it's probably the worst design ever... ;-)

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    3. They do have liquid in them, but heatpipes aren't considered "liquid cooling systems" because the fluid is sealed in them and the heat diffuses passively through to the heat exchanger through vapour-liquid transition rather than using an active pump to move the hot liquid around.

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    4. Thanks a lot for the explanation! :-)

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  2. I still use my PPC 1.8 ghz air cooled tower for a variety of tasks. Personally I prefer the air cooled to the liquid cooled PPC. Maybe my Mac isn't as fast but the machine runs 24/7 and gives me little or few issues to complain about. (and I've never had or will have a leak!) Just my 2 cents . . .

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    Replies
    1. I forgot to mention my 1.8 ghz is a DP model!

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  3. FYI, RenéRebe upgraded a single socket G5 to a air cooled 2,5GHz CPU:
    https://twitter.com/ReneRebeTM/status/1167837104824639489

    Maybe a LCS is not needed anymore.

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    Replies
    1. Single socket, though. Not sure how well that would work for the Quad.

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    2. The Quad runs fine with one CPU removed and doesn't even balk at the lack of an LCS. As long as you install CPU A back in the same slot it was in to start with you don't even need to run a thermal calibration. I know from experience, I also use my G5 for development and have even added an NVMe SSD and Radeon HD6670 which are both supported under Linux and don't cause issues in OS X other than sleep not working.

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    3. That's not what I meant. One CPU is obviously a lot cooler running than two.

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    4. Of course. The air cooler that ships with single socket machines occupies more than half of the space that the LCS does so you'd have to get creative in order to air cool both CPUs. I reckon a couple of Noctua heatsinks would probably do the job if you could figure out how to mount them.

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  4. CK - Have wondered if it might be possible to put an M.2 / MVME upgrade card into that 8X slot? While you'd obviously have to find one with auto-trim (garbage collection) and might need to do some testing, I wonder if you might really open-up that G5's Hyper-Transport with such a system disc? They really cheap (the cards anyway). https://www.ebay.com/itm/143180485808

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    Replies
    1. Yes, but it only works in Linux because Leopard has no support for NVMe in the kernel. Bearing in mind it's PCIe 1.0 and most SSDs are only x4 the performance isn't amazing but it definitely speeds up my compile times.

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    2. If you want the fastest possible storage for OS X then you should consider something like the Sonnet Tempo SSD which lets you add two additional internal SATA SSDs in RAID and works from 10.4 onwards.

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