Thanks again for the help on this!
I'll be using a sacrificial PU-18 for experimentation, so I'll take a look at the GPU and see where I can go from there.

There is no pinout for the GTE, because it's not a separate chip. It's implemented as part of the main CPU, and it's not even possible to monitor the signals to it because it's on the R3K coprocessor bus which isn't bought out to pins on the package. Thanks very much for the information. I meant th...

Hi, Does anyone have a good quality copy, OCR'd would be great, of the SCPH-5500 service manual? The only one I can find on the net so far is pretty janky in terms of quality and readability. Alternatively, if anyone has a pin-out and block diagram for the GTE chip in the SCPH-5500 that would also b...