Hi everyone,
I wanted to share a small update from my recent PowerPC G4 projects.
First, I was able to successfully upgrade an iMac G4 USB 2.0 / 167 MHz bus machine with a 7447B running at 2.0 GHz.
The machine is based on the later iMac G4 logic board:
iMac G4 USB 2.0
167 MHz system bus
Boot ROM 4.7.8f1
7447B at approximately 2.0 GHz
Leopard 10.5.8
With the 167 MHz bus, the CPU is running at approximately:
167 MHz × 12 = about 2.0 GHz
The machine boots into Leopard 10.5.8 and is usable. System Profiler reports the CPU speed correctly at around 2.0 GHz.
One interesting observation is video playback. On this machine, Movist is extremely compatible, but very heavy. In some cases, it struggles even with 480p video. However, CorePlayer performs much better, and I was able to play some fairly large 720p MP4 files surprisingly well.
So for this iMac G4, CorePlayer seems to be the best performance-oriented player, while Movist remains very useful as a compatibility fallback.
I also tested the Apple iSub under Leopard. With the iSub patch and a small activation workflow, the iSub works properly on this iMac G4. Interestingly, the same iSub patch did not properly activate the iSub on my G4 Cube under Leopard, so the iMac G4 seems to be a much better candidate for an iSub-based Leopard audio setup.
The machine is currently waiting for improved cooling before I do more long-term testing. Since the optical drive is removed, I expect the airflow path to be better than stock, but I still want to re-check the CPU die contact, heatsink pressure, thermal paste, and fan setup before running long stress tests.
I also want to sincerely thank Herd for bringing my PowerLogix Dual 7448 1.6 GHz Cube CPU card back to life.
This card was not merely unstable. It was essentially dead when I sent it to him.
It had serious power/bypass-related problems and would not work properly. I honestly thought the card might be lost for good. Considering how rare PowerLogix Dual 7448 cards for the G4 Cube are, this was a very special and important repair for me.
Herd diagnosed and repaired the card, including work around the power/FET area, and thanks to him the card is alive again.
For me, this was not just a normal repair. He revived a rare and important PowerPC upgrade card that I thought might be beyond recovery.
My next step is not to repair the card anymore — Herd has already done that. My job now is to install it carefully in the Cube, prepare proper cooling, and test it safely.
Herd recommended using thermal pads around the FET area. Looking at the board, I believe the relevant parts are the black SO-8 style MOSFETs around the inductors in the power section. My understanding is that the intended thermal path should be:
FET / MOSFET
→ thermal pad
→ PowerLogix bypass heatsink / metal plate
→ airflow from the Cube base fan
The FETs sit lower than the nearby inductors and capacitors, so I will need to choose the thermal pad thickness carefully. The pad needs to touch both the FET and the heatsink, but it should not be so thick that it bends the PCB or presses too hard on surrounding components.
For the CPU dies themselves, I plan to use proper heatsink contact and thermal paste, not a thick thermal pad.
At this point, the PowerLogix Dual 7448 card has been revived. I’m simply preparing for safe installation, cooling, and testing inside the Cube.
Thanks again to Herd. He did not just fix a small fault; he brought a dead and rare PowerPC upgrade card back to life.
And thanks to everyone here who continues to document and preserve knowledge about these old PowerPC machines. These projects are very niche, but they are still fascinating, and I’m happy to see these machines continue to live on.
