Question for those who have rebuilt a G5 quad lcu

[amishallin]

I'm in the process of doing a complete tear-down of a G5 quad I got on Ebay. The machine does boot to desktop but overheats soon after. To my surprise the machine looks like it saw little or no use at all. The only place I found some dust was on the cutting edge of the fans and even that was minimal.

I was expecting the back to be dirty (especially the fins) but I removed it anyway to replace the old crusty thermal compound. Have some leftover thermal paste from a PC I built not too long ago.

Again, I was expecting this to be a dust bunny farm. Some minor dust on the fans and the holes in the rear. Looks almost brand new.

Aside from the discoloration around the rear exhaust and the crusty pad it looks almost unused. I did break 1 of the plastic spring loaded pins holding down the upper heat sink... but fitted it with a nylon screw/bolt. The 6-pin connector came with an ATI x1900 found on Ebay. Original hard drive contains an installation 10.4.11 with Final Cut Studio 2 and Aperture 2. The 2.5" ssd has an installation of 10.5.8 that kernel panics seconds after the grey boot screen shows up. Have replacements for both drives.

Looks fine to me! BUT here is my question: are those circled hoses the same size (3/8" inner diameter 1/2" outer diameter) as the hoses on the top side? It doesn't look like there would be enough room for the standard hose clams I have. Are these hoses "ok" to leave? Plan on alternating between flushing with distilled water/vinegar for a couple hours and about 30min at 60C in a 30L ultrasonic cleaner a few times. Hopefully the LCU is the reason it overheats and i'm not looking forward to draining it.

That stock 6600 looks brand new... except for the dried up thermal compound.

Can't be seen in this image but the copper block for CPU A seems to have someones fingerprint burned into the center. My guess is whoever built it wanted to leave their "mark." Doesn't come off with 90% isopropyl but will most likely come off in the ultrasonic cleaner.

So far this hasn't been what I was expecting...

 

[ftalbot]

Hi. Nice machine.

There is a thread on 68kmla about that. Someone is even working on a way to replace the LCS with standards air coolers.

https://68kmla.org/bb/index.php?thr...ing-the-dual-pump-cooling-system.37474/page-3

 

[bkmoore773]

I have the same G5 dual-pump configuration. To your question, I believe the lower hoses are smaller size, but they should be standard sizes and be replaceable. The only way to know for sure would be to cut them open and take a few measurements.

My experience with the the G5 Quad: I did the new blood mod as described on 68kmla.org. But I do not have an ultrasonic cleaner, so I could only pump warm vinegar through the cooling system and hope for the best. In my case, I believe one of the cooling blocks has too much mineral deposits, and I couldn't get CPU B to properly calibrate. During use, CPU B would run about 20C warmer than CPU A.

In my opinion, the only way to properly service this cooling system would be to clean the cooling blocks separately in an ultrasonic cleaner to ensure there are no mineral deposits. Before I could even consider such a repair, one or both of the cooling pumps in my Quad appear to have failed. Since the pumps are practically unobtainable, and newer pumps aren't compatible with the firmware, I put my G5 Quad away and will probably sell it to someone who wants to attempt the repair, or who wants to convert it to air-cooling. I already sank too much money into my Quad at this point, so am looking at just getting rid of it.

I do also own a Dual-Core G5, same revision as the Quad. I upgraded it to a dual-core 2.5 GHz CPU and it works reliably and runs quiet. I serviced it, cleaned all the heat sinks, replaced thermal paste, and successfully completed thermal calibration. For most tasks, the speed difference is not really perceptible. But now that I am attempting to edit video on it using Final Cut Pro, the Quad would probably have been a nice upgrade.

 

[amishallin]

I posted on the 68kmla post mentioned above but figured i'd post an update here. The reason this seemingly unused machine overheats has been found (assumed it would be like this). I also accidentally screwed up the fins in the radiator during this operation and will have to spend time straightening them. Damage is mostly on the front side. Be very careful NOT to touch them!

This is the remains of the Dexcool in both loops. There was about 5oz total.

Not a whole lot of fluid came out of this side. Notice the corrosion. It almost got past the rib.

This side had most of the fluid. Looks like it was starting to make its way past the rib but was stopped by the hole clamp. I asked this at 68kmla also but do the rubbery/silicone pieces around all 4 ports coming out of the radiator need to be removed? It's hard to see with images of the completed mod.

Another note: these clamps come off easier when these little tabs are broken. It's easy to rotate the clamp to expose these by grabbing the crimp with a pliers.