HP 9872B Plotter

I have an HP 9872B plotter in my collection that is in very bad condition. There is a short circuit in the power supply somewhere. The foil on the paper surface has come off. I noticed that the HP 9872B plotter has a card slot. Does anyone know what it is for?

I think I’ve found the reason for the fuse blowing. Perhaps a short-circuited diode. With the variable transformer I already have 2 A at a few volts. I found a diode with a short circuit. Maybe I have a suitable one in my spare parts store.

I swapped a few filters. I didn’t have the right values ​​but I improvised.

YES!!! Successfully repaired! Three of four diodes replaced. The HB 9872B plotter has come back to life!

The missing HP logo was replaced with an original one. Everything was cleaned and the HP 9872B plotter was ready.