• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

PowerMac G4 MDD 1.25GHz DP Upgrade

mattsoft

Well-known member
Hi all - I have a PowerMac G4 MDD that is the dual firewire 400 model with dual 867MHz G4s on the CPU module. Just picked up a dual 1.25GHz CPU module off of eBay and plugged it in and nothing. Plugged the 867MHz module back in and all is good again.

I opened up a return with the seller and he mentioned that this dual 1.25GHz CPU module would only work with a PowerMac G4 MDD with both firewire 400 and 800, and not with the model I have (firewire 400 only). To make matters worse, he said I probably killed the card when trying to run it.

A quick search on the google doesn't turn anything up about compatibility issues with multiple versions of the CPU module card for PowerMac G4 MDDs, so thought I check here if anyone is familiar with this.

Thanks!
 
Last edited:

Byrd

Well-known member
Hi mattsoft,

All may not be lost, your MDD has a 133MHz bus speed - the early dual 867 and single 1.0Ghz were specced at this, with all other models (a mixture of FW400 and FW800 shipped at a 167Mhz bus speed.

Your new dual 1.25Ghz CPU is set to run off a 167Mhz bus (at a 7.5X multiplier = 1250Mhz); it should in theory still run fine on your MDD @ 133Mhz bus x 7.5 = 1000Mhz. However, stranger things have happened for a higher clocked CPU to not want to run at a slower speed. There is no way you've killed it. You need to relocate a resistor on the CPU daughtercard to a 9.5X multiplier to get it to work at the rated speed.

The seller has misinformed that the CPU works in all MDD models as they have a differing bus speed. I'd try once more and clean the motherboard and CPU daughtercard connector with electronic solvent spray, firmly reseat the CPU and press the CUDA switch on the motherboard, then try again.

JB
 

mattsoft

Well-known member
Thanks Byrd, I'll try it again tomorrow.

If it still doesn't work, you think it's worth it to change the PLL resistors on the CPU module to a 9.5x multiplier (133MHz bus x 9.5 = 1267) which should be close to the speed of the CPUs? The modification looks pretty simple to do. The eBay seller will not take it back, so I'm stuck with it. Might as well have some fun with it. :)
 

mattsoft

Well-known member
It looks like I can change the bus speed of the CPU module with a single resistor from 167 to 133. So I might try that first if the CUDA switch does nothing.
 

Byrd

Well-known member
Was just going to say same - yes I’d go the bus speed clock up, just make sure your RAM can handle the speed
 

Franklinstein

Well-known member
Older SDRAM-based models like the QS and earlier used bus-sync'd RAM, so matching RAM speed to bus speed would be a concern there. However the MDDs used 333MHz DDR regardless of bus speed (it's fixed to its own clock, not CPU bus clock) so it shouldn't be an issue.
 

mattsoft

Well-known member
I cleaned the socket with some deoxit and plugged the dual 1.25GHz CPU module in, hit the CUDA button, and pressed the power button and nothing. I then tried just holding the power button and a poof of white smoke came from under the heat sink.

So I remove the CPU module and put my 867MHz back in and the G4 works fine. I couldn't find any damage on the 1.25GHz module, but the white smoke and smell of burnt electronics are obvious signs that something ain't right with the module. At this point, I'm going to give up, e-cycle the module, and stick with the dual 867MHz for now.

The seller is quite adamant that this module will not work with a firewire 400 model, only the firewire 800 model, so maybe he's right.
 

herd

Well-known member
Wow, that doesn't sound good at all. I'm glad your MDD is still working. If you're going to scrap that CPU, I'd be interested in it for parts (if you're in the USA).
 

mattsoft

Well-known member
Wow, that doesn't sound good at all. I'm glad your MDD is still working. If you're going to scrap that CPU, I'd be interested in it for parts (if you're in the USA).

Sure, you can have it for shipping. I'm in WA state and will happy ship it to ya.
 

k24a1

Well-known member
Ah yes, if that's an original 7455 I can definitely see an issue. I had a dual 1GHz card for my QS and it stopped working.

Couple years back I had a 2002 1.25GHz DP MDD and the CPU card also died in that. Sucks to be me, I suppose.
 

Nifty950

Well-known member
i know its kind of late now, but you should have filed a paypal dispute or something because I can tell you for sure that a dual 1.25 will run in an 867 at 1.0 - im doing it right now!
 
Top