Power Mac G5 Quad Overtemp and Checkstop

[mduser63]

I've got a new (to me) Power Mac G5 Quad that was in supposedly working condition. When I got it, it would boot to OS X fine, but after a minute or so of running, would hang and the overtemp and checkstop LEDs on the logic board would come on. I suspected the liquid cooling system, so I took it out and rebuilt it. Completely flushed the radiator, disassembled and cleaned the water blocks, flushed the pump, replaced all the hoses and clamps, filled it with new coolant, and bled the system. I also replaced the thermal paste on the CPUs with Arctic Silver 5. I'm pretty confident in saying that the LCS is working well now. To be honest, I think it was working OK before, based on tests with the pump running and a heat gun. It's the single pump Delphi system, which was supposedly reliable-ish.

Anyway, having reassembled the machine, it's behaving exactly the same way. It will boot, but shortly thereafter it hangs, the fans ramp all the way up, and the overtemp and checkstop LEDs are on.

I'm wondering if anyone else has seen this, and can recommend other things to look for? It being able to boot tells me that the CPUs themselves are likely OK, and the CPU daughterboards are seated. I've also verified that the airflow deflector sensor is working OK, and that it detects that the deflector is seated. Both the front and rear fans for the CPU/LCS assembly are spinning. As far as I can tell, the LCS pump is receiving power and is running. I can feel it start vibrating slightly when I power the machine up, anyway. Are there other sensors that could be bad? Loose connectors to check for? Any help is appreciated.

 

[AphoticD]

What are your temperature readings while running? Try dropping performance to "Reduced" in Energy Saver settings. This may allow the Quad to stay upright for longer.

What kind of coolant and thermal compound did you use?

Would it be worth applying fresh thermal paste on the logic board ICs under the black heatsink too?

EDIT: Also try removing RAM in pairs. Certain modules might be causing excessive heat?

 

[Eriamjh1138@DAN]

Did you clean the heat sink on the back of the Mobo?

http://thehouseofmoth.com/a-little-...-mac-g5-and-what-to-do-with-this-information/

 

[mduser63]

What are your temperature readings while running? Try dropping performance to "Reduced" in Energy Saver settings. This may allow the Quad to stay upright for longer.

What kind of coolant and thermal compound did you use?

Would it be worth applying fresh thermal paste on the logic board ICs under the black heatsink too?

EDIT: Also try removing RAM in pairs. Certain modules might be causing excessive heat?

I used Arctic Silver 5 thermal compound (a very thin layer), and XSPC EC6 clear coolant.

At this point, I can't seem to get it to boot all the way to the OS X desktop. Not sure what's changed. It tends to hang shortly before the desktop is up.

It had 12 GB (6 x 2GB) of RAM. I've removed all but one matched pair with no change there.

Did you clean the heat sink on the back of the Mobo?

http://thehouseofmoth.com/a-little-...-mac-g5-and-what-to-do-with-this-information/

I didn't even know about this! It's going to be a bit of a pain to get the logic board out so I can do that, but I'll try it this weekend.

 

[1042686]

I know everything is pointing to a temperature issue but the only time I've experienced consistent freezing on bootup prior to the desktop was due to a gpu failure (PBG4 12"). Try pressing shift (safeboot) key when you start the machine and see if it boots to the desktop using integrated graphics.

 

[fourbirds]

I just finished refurbishing my own dual pump quad G5. I experienced the same exact symptoms as you. It took me close to 10 attempts at properly bleeding and flushing the system out. Every time I reassembled everything back together, I would get a different result. Either the system would not even fully boot before an over temp light would come on or it would boot with one cpu remaining cool and the other operating at close to 75 degrees Celsius. My three main issues were:

(1) not properly flushing the system out. The cooling blocks have a type of pressure adjusting thing-a-ma-bob in them. If any itty bit of pink nodules dislodged itself from the radiator, it immediately clogged the cooling blocks. This would not manifest itself immediately. On some attempts, it took over 5 minutes of pumping for the flow to stop/be reduced to a trickle. I ended up using an external 12v pond pump to run a 50/50 hot water and vinegar solution through both blocks in both* flow directions for an hour or so. I did the same with both sides of the radiator. This eventually produces a consistent flow through the blocks.

*I also noticed that while flow in the correct direction as indicated by the arrows on the blocks would eventually slow to a trickle, the flow if installed in the incorrect direction was not affected. I did not explore this further.

(2) air in the system. I replaced the S shaped metal tube with clear tubing with a T and valve. I also cut open both metal nubs off the radiator and added clear tubing and valves to both. This in combination with my external 12v pump made filling and bleeding the system very easy. I pushed the cooling fluid through my replacement S tubing and valve and bleed the air from the nubs off the radiator using the second valve. (I ended up using 28 hose clamps!)

(3) I am stubborn. If I had simply taken the time to do it properly the first time, I would not have sunk 30+ hours into this project.

My temps at idle are now hovering around 28 degrees Celsius. Good luck.

 

[Eriamjh1138@DAN]

Thanks for the update. I dread the day I have to do this to my QG5.

 

[fourbirds]

Having gone though my own G5's cooling system, I think I could get the dual pump system refurbished in under 2 hours. My stubbornness forced me to become an expert at taking it apart ...

To the OP, I would suggest you install istat to identify which of the cooling loops is overheating. Take the system apart once more and run hot water and vinegar through the cooling blocks individually using an external pump.

 

[Eriamjh1138@DAN]

Thanks for the update. I dread the day I have to do this to my QG5.

Old thread, but this day has come. My QuadG5 will not boot.

While there are no physical signs of leakage, I’m afraid the system is clogged or a pump has failed. Immediately upon pushing the ON button, the overtemp LED lights up. I have the version 2 processors and LCS. I am compiling the tools and parts needed for a tear down, rebuild, refill, bleed, and recalibration.

Wish me luck. Tips appreciated.