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Hello, welcome to the forum. There may be ways of tricking the installer, depending on what it's looking for. For real hardware limitations there may be a few; I think OS X needs at least 128MB of RAM to even boot, for example. One common approach to this sort of thing is to use a supported...

The external L2/L3 cache is configured with a register, via software. This can be done at boot through the firmware and/or after boot with software that has access to CPU registers. To get an idea what is happening at boot, look for a .pdf titled something like "Yosemite BootROM ERS.pdf" which...

This sounds like the CPU is melting down and the power supply is going into a current limit or short circuit protection mode. I'm glad you got it fixed; thanks for following up on your progress.

I don't think 0.5v is enough to run the CPU. What is the voltage when the CPU is not burning/scorching?

I would say that CPU needs a heatsink. Putting a bunch of power into a small area without cooling can quickly result in destructive temperatures. Consider how your soldering iron works. If you want to poke around on a running CPU board you could use a water block. These can be small and...

Welcome to the forum! That's a nice setup; thanks for sharing it with us.

Hello and welcome to the forum. It sounds like you have a pretty good grasp of the hardware situation. The various upgrades you mentioned may be quite noticeable, depending on what software you want to run. Some software uses a lot of memory bandwidth, and will benefit from faster bus and...

It doesn't seem to do anything but try to run scripts and install cookies. I just see a blank page. Anyway, it looks like you're doing nice work. Thank you for sharing your project with us!

Did any of the Powerlogix Pismo G3 upgrades use the 750G? ...or were they all the 750F? I used the firmware and mach_kernel patches from joevt to get the 750G working. I think a 750F would work without either. I don't remember hearing about patches for this stuff from Powerlogix, so maybe...

There are a number of differences between the "7400" G4 and the "7450" G4. You have the schematics for the iMac you were working on, right?

Nice, it looks like you're having fun. There is some more info and another patched kernel here: forums.macrumors.com/threads/os-x-tiger-on-a-603-604-cpu.1908276/ I found this useful because the same PVR problem occurs with 750G and 7448 CPUs. In the 750G thread joevt posted some good info...

Even better:

Do you have AppleFan.kext? This might do what you want: mac-classic.com/articles/mac-os-x-ppc-fan-control/ I'm sure there is probably 5v already available somewhere, like on the power board that the batteries plug into. I think the drive expects 5v. There is certainly 3.3v available, and a...

I put some CacheBasher results for a few different Pismo CPUs into a spreadsheet to compare them on the same plot: You can see that the memory/cache speed of the 750L G3 is significantly lower than the 7410 G4, until you get to the 750G which has 1MB of on-chip L2 cache at full CPU speed.

Interesting, I hope you can get some parts to test. They do look like different pins/spacing than these: 68kmla.org/bb/index.php?threads/6360-6400-6500-l2-cache-modules.38450/

To make things easier to edit, I use a USB stick. On computers that are difficult to boot from USB, I use a ZIP drive plugged into the IDE port.

Probably the biggest difference between the 750F and the 750G is the bigger cache. This shows a memory test of an 800MHz 750G, and you can see that the cache is almost 20x faster than RAM: ...so depending on what software you're using a bigger cache can help a lot. Here is a geekbench test...

I think either would probably work. You can try searching for PVR values in the firmware to maybe tell which are supported or blocked as described by joevt. It appears that the ZIF models can use 750F or 750G without modification, and these may be closely related to the iMac?

Thanks again to joevt for help with the firmware--I got a 750G working in the Pismo:

Did you already try a PMU reset with a good battery? PRAM reset? Does the USB or video power up? You could try pressing on the 300-pin connector while powering on. Of course if you have a different dual CPU board that does work, then it's pretty clear that the problem is with the CPU board...