For debugging purposes (and also for playing around with memory chips on a bread board) I’ve created little breakout boards for the cartridge slot on the bottom of Sharp PC-1500s/1600s.

I’ve added a layer of foam (not visible on the photo) on the bottom side of the cartridge to prevent the pin ends from scratching on the case.
Typing on the PC while having cables connected to the cartridge is a bit annoying as I tend to pull off the cables when turning the PC around. I’m currently figuring out a better solution by using ribbon cables instead of the pins. I will update the post as soon I’ve managed to make photos of the modified version.