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Newbie, G5 Quad

bkmoore773

bkmoore773

macrumors member
Original poster
Jun 14, 2022
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I just purchased a G5 from the local classifieds. It was only listed as a PowerMac G5, without any specifications. I took a gamble and it turned out to be a nearly mint-condition Quad. It was missing RAM and the HDD. I installed 2x2GB RAM and an old HDD I had sitting around and was able to install OS X 10.5 Leopard on it. This machine is in amazing condition for its age. It has the dual pump LCS configuration and unlike all the G5 Quad videos on YouTube, this one runs very quietly.

My questions to the group are, do I need to consider servicing the liquid cooling system any time soon? Should I replace the thermal paste on the CPUs? I would like to upgrade the graphics card from the stock 6600. Is there anyone out there who could flash an ATI Radeon for me? Or sell me one preflashed? I don't have a PC to do this on.

I intend to mainly use it for vintage mac gaming. I would like to play Halo Combat Evolved, StarCraft, Falcon 4.0, and any other old games I can get my hands on. This computer is probably overkill for that, but I don't care. It will be cool if I can track down a 30" cinema display. I have a set of SoundSticks to go with it.
 
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Congratulations! I own a PM G5 2.3 DP myself and these machines remain highly useable and capable. I hope that you have fun on the gaming front and you can never have too much horsepower when it comes to that. :)
 
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I really should get around to identifying all my stepfathers old Macs. Here in the attic I’m sure I spotted a computer with the exact same external case wrapped up in plastic bags. I wonder if it still works…
 
bkmoore773 said:
I was beginning to think the PowerMac G5 had a special YouTube firmware mode. If it detected a YouTuber filming, it automatically cranked up all the fans to full power to cool his ego off. :)
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Maybe most Quads are chronically camera shy and the overkill thermal dampening is because they're blushing?
 
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Edit: I put the G5 back carefully back together. Now both CPUs are running cool. mid 30s to mid 40s. I didn't remove the CPUs or reapply any thermal paste. What I did find is one of the wiring harnesses could possibly block one of the rear fans if not carefully routed. I made sure the fans were all clear when I reassembled the unit and everything is working within specifications.



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Quick follow up for the G5 gurus: I attempted the thermal calibration. The system appears to lock up, and two red leds come on on the Main board. I let it run for about 45 minutes, no progress or changes. When I run the system diagnostics, I get 100% pass on all systems and the system doesn't lock up.

The CPU A idles at about 40C and 60C under load which seems good. CPU B runs much hotter, about 60C at idle, 90C under loading. I downloaded the service manual and would like to redo the CPU thermal paste to hopefully get the temp on CPU B down. I followed the directions to remove the CPU, but as hard as I pull, the CPU won't come loose from the mother board. It almost seems like it's glued in place. I'll keep trying, but I don't want to force anything and break it.

I feel like a car mechanic, where one sticking fastener is keeping him from finishing the job and going home. I'm taking a break and will tackle the CPU again later. Anyone get the CPU out successfully? How hard do you really need to pull?
 
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There are like 12 bolts you need to remove from the processor heatsinks and the whole assembly should just lift out. You NEED to change the thermal paste on the processors and the u3 chip on the back of the board or you will continually have problems with it.
 
mustagcoupe said:
...the whole assembly should just lift out. You NEED to change the thermal paste on the processors and the u3 chip on the back of the board...
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YES!!! Agree 100%. I'm going to put using this computer on hold until I get that taken care of. I have the service manual and am following it to the letter. Unfortunately the CPU will not just lift out. I even put the case on the floor and used my whole body to try to pull the CPU out. No luck. I don't think there are any fasteners holding it in. Maybe it's stuck somehow from being in there all these years.

Other than that, this system is pretty easy to work on. If I could just get it apart, the rest would be very easy. I did recap the GeForce 6600, and it now works with the new capacitors. The old ones were leaking and bulging. Hopefully I'll be able to get the cooling system sorted out soon.
 
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You are missing one of the screws somewhere. i think there are 4 allen bolts around the perimeter of each processor card and then 2 recessed captive bolts way down in a difficult area per processor. You should have like 8 non captive allen screws and 4 captive bolts that wont come out of the processor. you are probably missing those captive bolts. If your having trouble look up a different writeup. The one for the dc 2.0 and 2.3 should give you an idea how to remove one processor. There are 2 in the quad but all the bolts are in the same places on the 2nd processor.
 
Edit: I believe the LCS on CPU B has failed. I did get the computer to boot, and the temp reported 102C before shutting down. CPU A was 30C.

Quick update: I finally got the whole unit apart. The service manual wasn't clear in the step when it said to loosen the 4 captive screws, but didn't say how much. I realized I had to keep loosening them until they came out. Then the CPU lifted right out. I repasted both chips on the mother board and both CPUs. When I reassembled the unit, it would boot to OS X, but then the red CPU overheat light would come on and the system would hang. I rechecked all the cabling and made sure everything was plugged in where it should be. I think I either reinstalled the CPU incorrectly onto the heat sink, or the LCS has failed on at least one of the CPUs.

I'm going to remove the heat sink again and reassemble the CPUs to it. If that doesn't work, probably the LCS has failed.

Any helpful advice would be appreciated. I really want to get this computer working right.
 
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bkmoore773 said:
Edit: I believe the LCS on CPU B has failed. I did get the computer to boot, and the temp reported 102C before shutting down. CPU A was 30C.

Quick update: I finally got the whole unit apart. The service manual wasn't clear in the step when it said to loosen the 4 captive screws, but didn't say how much. I realized I had to keep loosening them until they came out. Then the CPU lifted right out. I repasted both chips on the mother board and both CPUs. When I reassembled the unit, it would boot to OS X, but then the red CPU overheat light would come on and the system would hang. I rechecked all the cabling and made sure everything was plugged in where it should be. I think I either reinstalled the CPU incorrectly onto the heat sink, or the LCS has failed on at least one of the CPUs.

I'm going to remove the heat sink again and reassemble the CPUs to it. If that doesn't work, probably the LCS has failed.

Any helpful advice would be appreciated. I really want to get this computer working right.
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sometimes these old powerpc macs will just report the sensors wrong randomly. my g5 quad will sometimes say that it's running at over 1000 degrees celcius and then very quickly flip back to the actual temperature :p
 
Here's my plan: I'm a sucker and a fool who can never turn down an engineering challenge, :) and will get this machine sorted out. First I'm going to build a wiring harness to bench test the cooling system. That way I can tell if the CPU temperature sensor or the cooling system is bad. I am sure the coolant has degraded over time and the LCS needs to be serviced regardless. I will perform the New Blood Mod. If I'm successful, I should have a rock-solid G5 Quad that I can reliably use without worries for many years to come.
 
Tratkazir_the_1st said:
@bkmoore773
Apple manuals recommends to run thermal calibration after each CPU reinstall.
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I did some reading on this and the thermal calibration should only be run on a functioning system. I ran the system this morning with the cover removed, guitar pick in place to fool the system. I immediately noticed the liquid cooling system for CPU B is not circulating. Either the pump is bad, or the system has a blockage. I could tell this by simply touching the water return line into the pump. The return line on CPU A is warm. The one on CPU B is cold. I rechecked all the cabling and everything is connected properly.

I will service the cooling system and hopefully can salvage the bad pump or find a suitable replacement.

In a way this is actually very good news, because I know the CPU is good, the temperature sensor is good, and the problem is mechanical in nature. I can fix mechanical problems. If anyone knows what kind of pump is used in the version 2.0 LCS for the quad, please let me know. I'm assuming its a standard DDC liquid cooling pump.
 
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Yet another update. I picked up an air-cooled 2.3 MHz G5 Dual Core. After disassembling the Quad G5 it only took me a couple of hours to completely disassemble and clean the dual G5, re-paste all the heat sinks, and run thermal calibration. Unless you're the kind of person who likes to unclog toilets and work with hazardous chemicals, if you're getting a G5, get an air cooled one. :) :apple:

Back to the quad. I disassembled the CPUs from the LCS again, but this time, I went much further disassembling the floating plates and covers. You can see in the image, the heat transfer block for CPU B shows signs of leakage. CPU A also shows similar signs, but is much less severe. I'm thinking due to the heat, any leaked fluid immediately evaporated or boiled off before coming into contact with the CPU card.

This cooling system has two independent cooling loops. My theory is the loop that was cooling CPU B lost too much fluid and ran dry. I'll drain the system soon to confirm. Hopefully the pump is still good, but at this point I'm thinking about replacing the pumps with new, modern ones just to be sure. Getting my G5 Quad working correctly has become a mission...
 
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First a disclaimer, I never set out to buy a G5 Quad or any other liquid-cooled G5. When I answered the ad on CL, there were no specs. I wanted a dual core or dual processor air-cooled one. I also never set out to rebuild a water cooler and this is my first experience ever touching one. But I know if I didn't repair the LCS, this G5 would probably have wound up in the scrap pile, and working G5 quads are very rare.

Quick update, I drained the cooling system today. I only recovered about half the amount of fluid I expected. I took all the safety precautions. The system had lots of air in it, and there was a lot of sediment in the drained coolant. I'll dispose of it properly. This stuff is nasty.

I was able to remove the hoses without damaging radiator. I ran about 8 liters of distilled water (4 liters per side) through the radiator. Cooling loop B, the one on the left in the picture, was initially blocked, confirming my theory that the loop had failed and wasn't cooling the CPU. I was able to get it unblocked using water pressure, and water flows freely with no resistance. I'll boil some water and vinegar and run it through the loops to make sure everything is clean and clear. I only want to do this job once. Hopefully the pumps still work.

I repeat: DO NOT BUY A G5 QUAD, UNLESS YOU WANT TO REBUILD AN LCS!!! These things are time bombs.

If I can get this LCS working as new again, this will be an awesome computer and hopefully will provide many years of enjoyment as a vintage Mac. I'll have the ultimate PowerPC, and it won't sound like a leaf blower.
 
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bkmoore773 said:
View attachment 2027769

First a disclaimer, I never set out to buy a G5 Quad or any other liquid-cooled G5. When I answered the ad on CL, there were no specs. I wanted a dual core or dual processor air-cooled one. I also never set out to rebuild a water cooler and this is my first experience ever touching one. But I know if I didn't repair the LCS, this G5 would probably have wound up in the scrap pile, and working G5 quads are very rare.

Quick update, I drained the cooling system today. I only recovered about half the amount of fluid I expected. I took all the safety precautions. The system had lots of air in it, and there was a lot of sediment in the drained coolant. I'll dispose of it properly. This stuff is nasty.

I was able to remove the hoses without damaging radiator. I ran about 8 liters of distilled water (4 liters per side) through the radiator. Cooling loop B, the one on the left in the picture, was initially blocked, confirming my theory that the loop had failed and wasn't cooling the CPU. I was able to get it unblocked using water pressure, and water flows freely with no resistance. I'll boil some water and vinegar and run it through the loops to make sure everything is clean and clear. I only want to do this job once. Hopefully the pumps still work.

I repeat: DO NOT BUY A G5 QUAD, UNLESS YOU WANT TO REBUILD AN LCS!!! These things are time bombs.

If I can get this LCS working as new again, this will be an awesome computer and hopefully will provide many years of enjoyment as a vintage Mac. I'll have the ultimate PowerPC, and it won't sound like a leaf blower.
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This is great to see. Please keep us abreast on the progress. I'd love to get a G5 quad but, for the reason you stated, I've avoided any liquid cooled G5.
 
Today I successfully ran both cooling pumps. They both work!!! I ran each pump for several minutes on a homemade test rig. Now all that's left is to connect the hoses, fill the cooling system, purge the air, bench test it, then install it back in my G5. I posted a short video of the cooling pumps running.

 
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I need some help from the Mac Community: When I attempted to reassemble the heat sink to the CPU cards, I noticed one of the spring-loaded fasteners was stripped and cannot be assembled. Without this part, the CPU will not make good mechanical contact with the cooler and it won't work. I scoured the web for a replacement part, but to no avail. If anyone happens to have an extra set of G5 CPU to heat sink spring-loaded screws, I would be very happy. This part appears different than the ones used in other G5s.

If I cannot find an OEM part, I will try to find a standard part with the same thread and length. I pride myself on being a master mechanic and to have stripped a fastener is very embarrassing. :( But this project, almost went too smoothly and until this point, I haven't encountered any problems all. It went too smoothly...

That being said, I bench tested the water cooler. It has no air, and no leaks. It will work once I get the unit properly reassembled. But I see no reason to proceed until I can properly reassemble the CPU cards onto the heat sinks.
 
bkmoore773 said:
If I cannot find an OEM part, I will try to find a standard part with the same thread and length. I pride myself on being a master mechanic and to have stripped a fastener is very embarrassing. :( But this project, almost went too smoothly and until this point, I haven't encountered any problems all. It went too smoothly...
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It happens to the best of us. I do a lot of old computer repair / restorations and, given their age, thing inevitably break no matter how careful you are.
 
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I ordered a threading die. I'll attempt to repair the thread. If that doesn't work, I found a suitable standard part that should work. In that case, I'll replace all four fasteners with the standard part so the heat sink has an even pressure on the CPU. Obviously, finding the OEM replacement part would be best.

The vintage computer Gods had to make sure this project has at least one bump along the way.
 
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