Vintage Calculators

[peter scott]

Ah, if we're getting into the big boys I also have an HP9100A with CRT display and core memory sufficient for 50 program steps and also a magnetic card for program storage. It was introduced in 1968.

Peter

I've really been struggling to resurrect this machine. Unfortunately the service manual only covers the keyboard, power supply and display. All the other assemblies were serviced in the field by board swapping. With my very limited knowledge of what signals I should see I have been attacking it brainlessly by shot-gunning. Testing every one of about 350 transistors and many more diodes. I did find a faulty transistor in one of the many flip-flops and managed to get the arithmetic keys working but the trigonometrics and hyperbolics still resulted in a blanked display. The more I tried, the more it went wrong. I did come across a clock signal that wasn't getting to where it should. This was due to a faulty edge connector and what with the changing nature of the faults I concluded that all the motherboard edge connectors were suspect.

At first I thought that all the connections were not sitting proud of the plastic separators and tried carefully bending them slightly forward but to no avail. Looking at them under a microscope showed me that they weren't configured the way I thought and there was no way the separators were in front of the connectors.

   

I then tried washing the motherboard in the dishwasher but that made no difference to the faults. Deoxit contact cleaner was recommended to me but that made no difference either.



The edge connectors are mounted in a multilayer board that also includes a large amount of diode resistor logic and I don't fancy trying to desolder them.

I can see me admitting defeat with this thing.

Peter