Custom Air Cooling Mod for PowerMac G5 (7,3) Dual 2.5GHz — No More LCS!

[yucel_kandemir]

Hey everyone,
I’ve got a PowerMac7,3 Dual 2.5GHz G5 (originally liquid-cooled).
I completely removed the Panasonic LCS and replaced it with two Thermalright Assassin 90 Peerless White air coolers.


At first, I even tested it without any fans — just pure passive cooling.

• Idle: CPU A ~62°C, CPU B ~54°C
• Under full load (both CPUs): system reached ~110°C and automatically shut down (thermal protection).

Now with fans installed (case open, idle test):

• CPU A Die: 35.1°C
• CPU B Die: 31.3°C

Under real load (Photoshop, Dreamweaver, Fireworks, Flash, Illustrator all open):

• CPU A peaks around 78°C

Everything’s stable and quiet.
The machine runs macOS 10.5.8 and the temps are measured with Temperature Monitor 3.1.


Also, just a note for anyone who has worked with these Panasonic LCS units —
on the single-core 970FX models, the CPUs are not mounted directly on the logic board, but on the aluminum base of the liquid cooling system itself.
So converting this model to air cooling is not at all like the common G5 Quad mods where the heatsinks bolt to the CPU daughtercard.
This one is much harder to adapt.


I also took photos at every step of the process — every part, every modification — but unfortunately I can’t upload them here.


Has anyone else tried air-cooling mods on the liquid-cooled G5s?
I’d love to see your results or mounting ideas.

 

[TheShortTimer]

Welcome to the forum and congrats on your technical achievement!

I also took photos at every step of the process — every part, every modification — but unfortunately I can’t upload them here.

Doesn't "insert image" from at the top of the message window work for you? If you use that and drop the images inside the window, they'll attach to your post. Otherwise you could share them using an image site like Imgur.

(I used to be an Amiga devotee. Which model/models do you/did you have?)

 

[eyoungren]

Might want to talk to @mac57mac57

https://forums.macrumors.com/threads/comprehensive-guide-to-converting-g5-quad-to-air-cooling.2457994/

 

[Doq]

Also, just a note for anyone who has worked with these Panasonic LCS units —
on the single-core 970FX models, the CPUs are not mounted directly on the logic board, but on the aluminum base of the liquid cooling system itself.
So converting this model to air cooling is not at all like the common G5 Quad mods where the heatsinks bolt to the CPU daughtercard.
This one is much harder to adapt.

This is only relevant if you plan on keeping any of the LCS structural pieces, though the hole locations on these earlier processor cards do look different, so maybe a bit of origami is required.

For what it's worth, while it looks like modification to the processor may be required for 970FX models, on 970MP models the modifications have to be done to the logic board instead.

I'm still waiting on an early LCS model to come in to do a similar modification.

 

[yucel_kandemir]

This is only relevant if you plan on keeping any of the LCS structural pieces, though the hole locations on these earlier processor cards do look different, so maybe a bit of origami is required.

For what it's worth, while it looks like modification to the processor may be required for 970FX models, on 970MP models the modifications have to be done to the logic board instead.

I'm still waiting on an early LCS model to come in to do a similar modification.

I think there is a small detail that might have been misunderstood. On these systems, the heatsinks are normally mounted directly to the CPU daughterboard, and the contact pressure on the die is determined by the distance between the heatsink base and the board itself — which is absolutely critical. In my case, since the Panasonic LCS design provides no mounting points on the CPU board for attaching a heatsink, I had to precisely control that pressure by adjusting the washers under each screw. This was the only way to achieve proper thermal contact without risking damage to the processors.

One point may have been overlooked: the CPU daughterboard is secured to the logic board only via the aluminum plate that is part of the LCS — there is no other attachment method.

As you can see in the picture, the motherboard doesn’t have holes in the correct positions, and these are not screws — they’re actually nails. Even if I replace the nails on the processor boards with screws, only two screws wouldn’t be enough to support the weight. So I have no choice but to use the LCS plate.

Therefore, without the LCS plate, the daughterboards cannot be secured to the motherboard, which makes mounting these boards onto the motherboard extremely difficult. I hope I was able to explain it clearly.

 

[yucel_kandemir]

Might want to talk to @mac57mac57

https://forums.macrumors.com/threads/comprehensive-guide-to-converting-g5-quad-to-air-cooling.2457994/

I’ve seen that project, and it’s a really clean and impressive piece of work. However, in systems like mine with dual 970FX processors, air cooling is extremely difficult and requires a high level of technical skill. As I explained to the other person, the heatsink cannot be mounted directly to the processor card, as the card has to be secured to the LCS plate, not the motherboard. This makes it incredibly difficult to mount the heatsink at the correct height, angle, and pressure on the processor, especially at the proper 90-degree angle. In quad systems, they simply tighten the spring-loaded screws after mounting, but this is not possible with the 970FX. Additionally, the die of the 970FX is only half the size of the MP’s die, so even the smallest angular misalignment could crack the die. This is the main reason why this project is so challenging.

 

[Doq]

I think there is a small detail that might have been misunderstood. On these systems, the heatsinks are normally mounted directly to the CPU daughterboard, and the contact pressure on the die is determined by the distance between the heatsink base and the board itself — which is absolutely critical. In my case, since the Panasonic LCS design provides no mounting points on the CPU board for attaching a heatsink, I had to precisely control that pressure by adjusting the washers under each screw. This was the only way to achieve proper thermal contact without risking damage to the processors.

One point may have been overlooked: the CPU daughterboard is secured to the logic board only via the aluminum plate that is part of the LCS — there is no other attachment method.

As you can see in the picture, the motherboard doesn’t have holes in the correct positions, and these are not screws — they’re actually nails. Even if I replace the nails on the processor boards with screws, only two screws wouldn’t be enough to support the weight. So I have no choice but to use the LCS plate.

Therefore, without the LCS plate, the daughterboards cannot be secured to the motherboard, which makes mounting these boards onto the motherboard extremely difficult. I hope I was able to explain it clearly.

Ah, I think I get it now. Yeah, if you really want to ensure secure attachment of the processor cards, then keeping as much of the attachment hardware is necessary.

On my 970MP modification the only secure attachment the processors have is the socket itself and the grounding screws on the backside (there being basically no clearance between the coolers and the PSU and PCI plates helps a lot), but now that I see these FX cards are missing the backside grounding, maintaining the mounting hardware makes sense.

 

[yucel_kandemir]

Ah, I think I get it now. Yeah, if you really want to ensure secure attachment of the processor cards, then keeping as much of the attachment hardware is necessary.

On my 970MP modification the only secure attachment the processors have is the socket itself and the grounding screws on the backside (there being basically no clearance between the coolers and the PSU and PCI plates helps a lot), but now that I see these FX cards are missing the backside grounding, maintaining the mounting hardware makes sense.

That's exactly why converting the 970FX modules to air cooling is such a difficult process. I really wish more of these machines were still around — maybe someone could eventually find a more practical solution. Even with my technical background, I had to dedicate two full days of work just to make this modification possible.