There’s an error in all of the the Sharp PC-1500 Technical Reference Manual versions I have come across so far: in the pinout of the 60-pin connector a pin is documented as being VBAT instead of F-GND. Your Sharp PC-1500 can be ‘killed’ if you short VBAT (Battery Voltage) to F-GND (Frame Ground).
If you look at the traces (here: taken from the Radio Shack PC2 Technical Reference Manual) you can see that pin 44 is connected to F-GND instead of VBAT. It is easy to verify this with a multimeter in continuity mode.
I have to admit that I also came across this ‘by accident’… so keep in mind to verify the documentation whenever possible. The corrected version of the 60-pin connector pinout should look like this:
Kai, so good to see you post pc-1500 stuff. In my Japanese version it also says pin44=vbat https://photos.app.goo.gl/xPkRQ9AKC1hwK6qW9