PowerMac G4 MDD unstable after bus speed mod

[croissantking]

I've installed a Dual 1GHz CPU in my MDD (formerly Dual 867), and bumped the bus speed to 166MHz by removing R676 on the underside of the logic board.

However, it now has RAM-related issues with stability that it didn't have before. Depending on configuration, it either fails to boot or kernels panics/freezes later on. The only configuration that seems to work is a single 1GB module in the slot nearest the CPU. If I add my other 1GB module back in, things become unstable again. FYI, both modules are PC3200.

Are the 166MHz bus MDDs usually this picky about RAM, or could it be that 133 boards don't always like being overclocked?

 

[alectrona6400]

I've had a G4 MDD that had issues at a higher bus speed, so I underclocked it back to 133MHz. A good amount of early G4 MDDs are like that in my experience. A good idea would be to get a motherboard that is already clocked at 167MHz if you're unsuccessful with the bus overclock.

 

[croissantking]

That would suggest there is some other difference between a stock 133 and stock 166 board. Perhaps there is another option resistor that needs to be set (voltage?), or maybe the bill of materials is different and there is a chip inline with the memory controller that's rated to a slower speed.

 

[alectrona6400]

Perhaps... I haven't looked into it in years.