9100A with no display now working!

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.)


Congratulations, nice machines. i don't think I will be bidding on ebay.


Yeah, that looks like my old machine. Congratulations on finding those open resistors! I probably checked everything in that machine except the resistors on that board.


And where in the world would one find NOS correct HP transistors?

I suppose that in order to have a complete collection, I should have a 9100A. But I think my investment in two restored 9100Bs has used up all my discretional calculator money for the next five years...


And where in the world would one find NOS correct HP transistors?

Hi Dave, I got the 1854-0354 transistors that were the output transistors on the braided core board from http://www.etestparts.com/. I've also ordered NOS parts from http://www.sphere.bc.ca/test/hpparts.html. BTW Sphere has a nice cross reference list on that link of hundreds of HP transistors & diodes. Turns out there was no x-ref listed for the 1854-0354 parts I needed. Keep in mind the abreviated marking HP used on these parts: These transistors are marked "4-354" which is really part number "1854-0354"


I just noticed you're right up the road from me, in Sparks (I'm in Reno).

Sigh. If I hadn't spent all my calculator funds for the next few years, I'd drop by and take a look. But there's little point in tempting myself now!

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