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Repair/Overhaul of PowerMac G5 Liquid Cooling System and CPU Boards
2.7 GHz Dual-CPU G5 built May 2005 - Delphi LCS

By Bill S.
Posted: July 22, 2010

(This is Page 4 of the 6 page article)

23) I used a 70% solution of isopropyl alcohol and an acid brush to finish cleaning the heat transfer modules. Figure 26 shows the results. Note the dark edges where the white contaminant had been; plating had been attacked by coolant.

HT modules cleaned
Figure 26. Heat Transfer Modules Cleaned

24) Attention turned to disassembling the LCS cooling system. First the system was drained. The LCS was held with the radiator held vertically on a diagonal with one spigot at the bottom. Coolant was drained into an oil drain pan. Hose clamps were retracted and hoses removed from radiator, coolant pump, metal lines, and heat transfer modules. Typical disassembly photos are below in Figures 27-29.

Radiator and Heat Transfer Modules
Figure 27. Radiator and Heat Transfer Modules

Bare Heat Sink Assembly 1
Figure 28. Bare Heat Sink Assembly (1)

Bare Heat Sink Assembly 1
Figure 29. Bare Heat Sink Assembly (2)

25) Next, the four flat head Philips screws mounting each heat transfer module were removed, which both released and disassembled the "HTM". A look inside the heat transfer modules shows contamination; see Figures 30 - 33.

Heat Transfer Module Interior (Dirty)
Figure 30. CPU A Heat Transfer Module Interior (Dirty)

26) The white OEM O-rings were very soft. Contamination was evident outside the circumference of the O-rings as well as inside the bottom section of the modules. The multi-finned mini-radiators were also somewhat plugged with contaminants.

Heat Transfer Module Interior (Dirty)
Figure 31. CPU B Heat Transfer Module Interior (Dirty)

27) The purpose of the white rectangle under the mini-radiator is probably both a mechanical and thermal bond to the top cap of the module. The fins are fragile and need to be kept evenly separated to allow all surfaces to pass coolant. Be careful when cleaning! I used an acid brush and alcohol.

Dirty Heat Transfer Module
Fig 31A. Dirty Heat Transfer Module

28) Figure 31A is a close-up of one HTM top cap and mini-radiator, showing typical contamination of heat transfer modules before cleaning.

Cleaned HTM
Figure 32. CPU A - Cleaned Top Inside of Heat Transfer Module

29) The surface shown in Figure 32 was cleaned with Amway Chrome & Glass Cleaner and a soft rag. This is a tricky job to maintain a flat surface for the O-ring, and still clean off all the contaminant while avoiding the mini-radiator. As you can see, the base material of the top cap is copper, with a silver-colored plating over it (nickel?). Near the edges, the contaminant had actually replaced the plating.

Inside HTM
Figure 33. CPU B - Cleaned Top Inside of Heat Transfer Module

30) The CPU B unit did not clean up quite as well as the CPU A unit, but the area under the O-ring is clean. This piece also was seriously attacked by coolant outside the circumference of the O-ring.

31) The bottom portion of the heat transfer assembly cleaned up nicely (see Figure 34). The new Viton O-Ring fits nicely in its groove. Figure 34A shows the mounting area for the HTMs (top side).

32) Before beginning reassembly, I ran tap water from a hose through most separate components - radiator, pump, and hardline tubing. I disassembled and inspected the pump while it was off the LCS, but found nothing wrong. Also, I replaced all the rubber hoses except for one, for which the OEM hose had to be used due to tight clearance between the radiator input port and part of a heat transfer module.

Bottom of HTM
Figure 34. Bottom Section of Heat Transfer Module

Topside of LCS HTM mtg area
Fig 34A. Topside of LCS - HTM Mounting Area

= Continue to Page 5 =

Index of PowerMac G5 LCS Repair Article

Page 1 | Page 2 | Page 3 | Page 4 | Page 5 | Page 6

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