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G5 CPU Upgrade

SuperKerem

SuperKerem

macrumors 6502a
Original poster
Oct 29, 2012
863
261
I have a question about my Dual Core 2GHz Power Mac G5 (Late 2005). Currently, it's disassembled and I have the choice of installing either a 2GHz CPU board or a 2.3GHz CPU board.

The 2.3GHz (native) system has a 1.15GHz frontside system bus while the one in my system is clocked at 1GHz. I was wondering if this impacts CPU compatibility in any way, or if there are any other differences I am unaware of?

I'll keep this thread updated as I attempt the CPU replacement.
 
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the motherboard and cpu's on the G5 are matched. you cannot upgrade the cpu's. if you even switch the cpus on the same dual machine you have to use the Apple Hardware Test disk to recalibrate the machine.
 
havokalien said:
the motherboard and cpu's on the G5 are matched. you cannot upgrade the cpu's. if you even switch the cpus on the same dual machine you have to use the Apple Hardware Test disk to recalibrate the machine.
Click to expand...

Not all of the logicboards have a locked system bus. There are a few models that allow for switching of slightly faster, yet same model year, CPU(s) without a problem. Running AHT is still required, but it works. I don't recall which models, but they do exist.
 
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As far as I know all the G5's are bus locked on the motherboard. You can put in a faster cpu, but it will run at the 2x of the motherboard clock. So the same speed as the original processors.
 
havokalien said:
As far as I know all the G5's are bus locked on the motherboard. You can put in a faster cpu, but it will run at the 2x of the motherboard clock. So the same speed as the original processors.
Click to expand...

When my late 2005 2.5 Quad LCS went bad, I placed the same year single 2.3 processor and fan assembly in my system with absolutely no problems at all. Everything was reported as it should have been, including all of the screw mounts.
 
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AmazingKerem said:
I have a question about my Dual Core 2GHz Power Mac G5 (Late 2005). Currently, it's disassembled and I have the choice of installing either a 2GHz CPU board or a 2.3GHz CPU board.

The 2.3GHz (native) system has a 1.15GHz frontside system bus while the one in my system is clocked at 1GHz. I was wondering if this impacts CPU compatibility in any way, or if there are any other differences I am unaware of?

I'll keep this thread updated as I attempt the CPU replacement.
Click to expand...
I have successfully upgraded a 2.0 GHz late 2005 dual-core to 2.3 GHz. The two models are identical but for the processor card, and they're all capable of the faster bus speed.
 
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Thanks for the responses! Unfortunately, due to an issue with the heatsink, I was unable to rebuild my Dual after numerous attempts. Based on what has been said, it seems to be the case that it would've probably worked fine.

Additionally, for what it's worth, I can confirm that a Quad can run with a single air-cooled CPU to replace the LCS with two CPUs. :)
 
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redheeler said:
I have successfully upgraded a 2.0 GHz late 2005 dual-core to 2.3 GHz. The two models are identical but for the processor card, and they're all capable of the faster bus speed.
Click to expand...


Id like to see that then as the motherboard bus is locked, at it sets the processor speed.
 
havokalien said:
Id like to see that then as the motherboard bus is locked, at it sets the processor speed.
Click to expand...

Not all of the G5 logicboard have a locked bus. I've done the same or similar upgrade as redheeler and rawweb. Some of them are, but not all of them.
 
havokalien said:
Id like to see that then as the motherboard bus is locked, at it sets the processor speed.
Click to expand...
System Profiler screenshot from aforementioned G5. Look up the serial number (I'll save you the trouble by linking it here) and you'll find its original clockspeeds.
Dual-core 2.3 G5.png

I'm confident this upgrade will work on any late 2005 model, but maybe not the earlier ones which you'll find most of the info saying it's not possible refers to. That is, provided your processor card isn't defective like mine was the first time I attempted this...
 
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redheeler said:
System Profiler screenshot from aforementioned G5. Look up the serial number (I'll save you the trouble by linking it here) and you'll find its original clockspeeds.
View attachment 685384
I'm confident this upgrade will work on any late 2005 model, but maybe not the earlier ones which you'll find most of the info saying it's not possible refers to. That is, provided your processor card isn't defective like mine was the first time I attempted this...
Click to expand...

Second that, I've tinkered around with most of the machines from the late 05 series. Good to go so long as one runs the calibrater after upgrade/downgrade :)
 
funny the site you show says The Power Macintosh G5 models have the processor(s) mounted on a custom 300-pin daughtercard, but it is not feasible to upgrade the processor.

Your screen grab shows the bus speed is more than stock, how was that achieved? Again it is hardware set. Ive seen fake software hacks showing older macbooks as faster ones before. Just trading the cpu will not allow the bus speed set by resistors to change.
[doublepost=1485358441][/doublepost]I have done resistor changes from 68k to G4 powerpc, but this is the first G5 ive seen.
 
havokalien said:
funny the site you show says The Power Macintosh G5 models have the processor(s) mounted on a custom 300-pin daughtercard, but it is not feasible to upgrade the processor.

Your screen grab shows the bus speed is more than stock, how was that achieved? Again it is hardware set. Ive seen fake software hacks showing older macbooks as faster ones before. Just trading the cpu will not allow the bus speed set by resistors to change.
[doublepost=1485358441][/doublepost]I have done resistor changes from 68k to G4 powerpc, but this is the first G5 ive seen.
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I don't think they have info specific to the late 2005 models. Easy to assume that what applies to the earlier models also does to the later ones, but in this case that is simply not true. All I did was swap the processor card, nothing else was modified. The system is running stable and saw a slight but noticeable performance boost from the upgrade.
 
I have put many faster processors in the dual G5 I have and with success of booting, even after AHT calibration the board stays at normal bus and the processor is down clocked.

I also found both processors needed to be matched part numbers or would not boot.

Again this is the first I have seen this in the open, so you will have to excuse me if I find it hard to believe.

Is it PCI-X I assume then?
[doublepost=1485362110][/doublepost]Its also strange the 2.5 processor using the same bus speed as the 2.3 so something is real strage here. All have a high logic board failure (par for the course with the G5's).
 
Again havokalien, not all of the G5's have a locked logicboard bus speed. There's nothing strange here when the speeds are no locked on that particular logicboard. I'd imagine this is a myth, similar to the one where PowerPC Macs cannot boot from a USB drive.
 
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havokalien said:
I have put many faster processors in the dual G5 I have and with success of booting, even after AHT calibration the board stays at normal bus and the processor is down clocked.

I also found both processors needed to be matched part numbers or would not boot.

Again this is the first I have seen this in the open, so you will have to excuse me if I find it hard to believe.

Is it PCI-X I assume then?
[doublepost=1485362110][/doublepost]Its also strange the 2.5 processor using the same bus speed as the 2.3 so something is real strage here. All have a high logic board failure (par for the course with the G5's).
Click to expand...
This is a Power Mac G5 (Late 2005) with PCIe expansion slots and a single dual-core processor.
 
Powerpc did not have USB support to boot, just like the 128 mb of ram for the SE/30. It was not tested at time of sale so not Apple certified and tested (unsupported).

The G5's you show seem to be an odd duck.

I will look into it more I guess but the G5s solder is lead free and with the high heat and flex of the motherboard, very high failure rate among all of them. I only keep powerpc to run OS9 when I do use it so the one G5 I have just sits at the moment.
 
Apple supported the booting of USB from the very start on systems that have dual-channel USB ports, such as the slot loading G3 iMac and Sawtooth. Here's the official KB article that outlines it: https://support.apple.com/kb/TA25908 It was tested, certified, and publicly documented by Apple when those machines shipped. Saying that PowerPC Macs cannot boot from a USB drive is completely inaccurate as most people on this sub-forum that have tried it have succeeded. On USB 2 Macs it's a bit more difficult, but fully possible.

Those G5's are not an "odd duck". It's been done to many different machines that are of the models that allow it.

G5's may have a higher than average failure rate for machines of that vintage, but they can and do last a good long time so long as they don't go through temperature extremes.
 
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Isn't it all a bit moot? Given how cheap G5s are, would it not be just as easy/cheap to swap out an entire motherboard/CPU combo? Ok sure it's a bit more screwdriver work but then there's no need to do the calibration and no guessing as to whether it will all work or not. I swapped my 2x2.7 CPU and board into a 2x2ghz case, just because the case was in better condition, and it all works.
 
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stampedeadam said:
Isn't it all a bit moot? Given how cheap G5s are, would it not be just as easy/cheap to swap out an entire motherboard/CPU combo? Ok sure it's a bit more screwdriver work but then there's no need to do the calibration and no guessing as to whether it will all work or not. I swapped my 2x2.7 CPU and board into a 2x2ghz case, just because the case was in better condition, and it all works.
Click to expand...

That's a good idea in theory, but it's worth mentioning that unless you're buying locally a complete G5 can be well over $40 to ship and a CPU card is usually under $10.
 
stampedeadam said:
Isn't it all a bit moot? Given how cheap G5s are, would it not be just as easy/cheap to swap out an entire motherboard/CPU combo? Ok sure it's a bit more screwdriver work but then there's no need to do the calibration and no guessing as to whether it will all work or not. I swapped my 2x2.7 CPU and board into a 2x2ghz case, just because the case was in better condition, and it all works.
Click to expand...
Swapping out the entire motherboard of a G5 is no small feat. Pretty much every last component must be taken out beforehand.

Replacing the CPU card is far easier, requiring only a handful of screws to be messed with. It also serves as an opportunity to reapply thermal paste :).

Although G5s are relatively cheap, it's not easy to find a specific model - especially if you're outside the US. They aren't as common as they once were.
 
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