Note: This is an ongoing project, check back for updates!
Link to the PlayStation 2 Service Manuals: Internet Archive Link
These service manuals provide invaluable information on the PS2s inner workings all down to the raw schematics. They were previously quite hard to find (it took me ages to track them down a few years back) But they are now easily accessible thanks to Internet Archive!
SCPH-300X Diagrams
The resistor arrays highlighted in pink are the ones that can be shorted via switches, pots etc. You can solder to either side of the resistor array.
GPU / CPU bends (top of PCB)
GPU / CPU bends (bottom of PCB)
Audio RAM bends (top of PCB)