1 Reply Latest reply: Feb 19, 2009 2:00 AM by japamac
JeffDy Level 1 (5 points)

Everyday I come and watch the growing number of failing G5 computers, other websites forums also point to the same main problem: BGA failures. And this is not only an Apple concern...
Let's go technical:
Read this:
http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/59BEA03A4FA9E41787256FD 600710800/$file/BGA%20Solution%20for%20G5.pdf

Temperature variations lead the solder joint, mostly in the corners of the chip to fracture. On the PowerMac G5 there is an underfill between the CPU chips and their boards. Maximum reliability then.


But under the Northbridge U3 (or U4 on late Quad G5) there is no underfill.


And even if CPUs are what everybody know and talk about, the Northbridge chip is the heart of the machine. Various troubles (no boot, kernel panics, only 1 operating CPU, no reboot after RAM addition) come from the fact that the contacts between this chip and the board are failing...

I quote a company who answered me it will cost 115$ for a reflow and 200$ for a R/R/R (stands for remove/reball/reflow) for the U3. You must send the motherboard only for this price and add shipping costs. It's also possible to add an underfill for maximum reliability...

It's possible to DIY a reflow with a heat gun and some skills. Some links on the web point to fixes made on the graphic chip of the iBook G3, on the XBox 360, on cell phones also. Good news is it will not be necessary to recalibrate if you put back the CPUs at the same place...

Important notes:
There is a small blower hidden behind the HD fan which drives fresh air under the board from the front of the machine to the hard drive bay. Mine was very dirty, half clogged by dust. It's tricky to remove it from the front of the machine and putting apart the whole case to remove it is boring as possible, but this blower is essential to cool down the backside of the board and keep the U3 to overheat. Since few people know it exists and so never clean it, there are lot of chances a lot of them are not working properly anymore...

Here are pictures of mine (4 years old)

Another problem is that the heatsink upon the U3 is not correctly applied on the chip for a rubber pad (glued on the heatsink) gets in contact with the board before the heatsink is level with it. And that leaves a gap (1/2mm) between the chip and the heatsink. I cut about 3mm off the pad to make things right. Here under the cut rubber pad picture.


And since all those G5 troubles are linked to alternate temperature variations, you should never let the machine get hot and cold too often. Keep it running everytime...

Hope it helps ;+)


Spare parts of G5DP2G, Mac OS X (10.5.6)
  • japamac Level 7 (24,385 points)

    Thank you for what appears to be a solid assessment of the conditions leading to logic board failure in G5's.
    Even more helpful, is the possibility of relatively economical repair.

    Regarding the repairs that you have made, we can assume that the repairs were successful in returning the machine to a stable, functional state?

    I know many will want to know as many specifics as is possible.....