This is the 9100A I posted about about a year ago. It was DOA at the time and I've been working on it on and off ever since. (Katie this is the one my son bought from Aristotle.) To make a long story short I replaced some generic transistors that the previous owner had installed with NOS correct HP parts and eventually traced the problem down to two open resistors in two ROM sense amp circuits - one on the odd side and one on the even side. It would have been impossible to locate the problem without Tony's incredible schematics! Thanks Tony!
The card reader had no issues and reads & writes without error.
The plotter platen surface had de-laminated and stretched. I peeled it off and cleaned off the old adhesive. I was able to find a perfect (imho) replacement piece of material at a car custom graphics shop. After cleaning the contact rails and linear potentiometers with some DeoxIt the plotter is back to 100% functional. The 43 year old pens are dried up but the plotter went through the steps of plotting a sine wave.
My son will be posting these on eBay on Thursday (12/8.)
