G5 late 2.5GHz CPU A thermal runaway

[jlofgr]

Hi Folks,
Haven't been on for a few weeks...thought I had my issue resolved, but apparently not all of it. No boot up problems and the G5 doesn't shut down on it own, but I think CPU A is toast from too much past overheating. This is a single pump 2.5. I rebuilt the LCU with flushing, hoses and coolant. New heatsink compound and all. I may have blown it by not doing a thermal calibration on the unit after all of this. CPU B sits at 33 degrees C all the time. CPU A will sit at 45 degrees C until you try to do something other than open firefox. Printing is too much of a challenge for it. It may jump to high 80's as long as your working. I don't dare process any video. I think it may be too late to run the Thermal calibration on it, but if someone has a link to it, I would be most appreciative. I'm about to go shopping on EBAY for a new 66-3729 processor. Any thoughts would be appreciated. I'm not quite ready to give up on this box yet.

Jim Lofgren- Redmond, WA

Late '05 2.5 GHz PPC with 8 GB Ram, 500 GB HD 1 GB Raid, Airport card, Gforce 7800, IPAD Mini 32 Gb, Wife's I7 IMAC 27" My G5 is her Handmedown.....(;]

 

[gavinstubbs09]

On one of my 2.7GHz G5s I rebuilt the LCS, and CPU/A would still be really hot. I swapped the top/bottom CPUs and that helped for heat as CPU/B gets fresh cold coolant from the LCS. Also find ASD (Apple Service Diagnostics) 2.6.3 and do a thermal calibration after swapping the CPUs to re-program the fans.

My 2 cents!

 

[jlofgr]

I thought the position determined which was A and B... Switching the CPU's shouldn't make a cooling difference to the A CPU, or am I totally off on that?

Jim

 

[gavinstubbs09]

I thought the position determined which was A and B... Switching the CPU's shouldn't make a cooling difference to the A CPU, or am I totally off on that?

Jim

The bottom CPU gets cold coolant straight off the radiator. The Top CPU gets the heat from the bottom processor as well, then it goes into the pump and back into the radiator. The difference in temps from the bottom and top CPUs is anywhere from 5-15*F differences.

 

[jlofgr]

Ok...I think I understand somewhat. Since B is on the bottom, It does make sense that the heat surrounding the CPU itself would be a little cooler, but the actual coolant in my model takes the same length path from the radiator and into the cooling blocks for the CPUs. Please correct me if I am wrong, the top CPU is always A and the bottom is always B. The Top, A CPU is always the primary one and the B bottom one is always the secondary. I had thought of changing the two just to make the undamaged B, the new A. Do you know where I might find a copy of the ASD? When you run the ASD, do you get to choose which one will be A?

Regards

Jim Lofgren

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Incidentally, this is a Quad if I hadn't mentioned it before.

Jim

 

[gavinstubbs09]

A is used all the time and B is still used, but not nearly as much usage as A. Swapping the 2 will make B the new A and vise versa. I can't specify here where to get it but find ASD 2.6.3 and burn it, then boot off the disc and at the top left there will be a calibration button, this will take a while and the G5 will act sluggish.

Some Quads had duals and some had singles. The dual was much less prone to leakage! If I recall the LCS in yours uses fuel line the entire way and doesn't have aluminum tubing like mine, although similar.