The article mentioned this needed a modified N64 to route the extra debug signals from the cartridge to the CPU. That got me wondering since afaik there are no unused cartridge pins on the N64.

Turns out it's actually a bit more complicated. The Partner-N64 uses some little-used analog input pins (LAUDIO, RAUDIO, VIDEO_SYNC) for this. The modification also requires cutting the lines to the system's DAC chip to work.

https://ultra64.ca/tutorials/make-your-own-partner-n64-conso...