WOW talk about your retro calculator HP 9100A


During my travels over the weekend, I stumbled across an HP 9100A. Forever the fool, I decided to buy the $50.00 boat anchor in an "unknown" condition. There was no available AC cord for a quick test. I just knew that the CRT would be dead after 40 years.

I broght it home and finally found the old style AC cord I had stashed away. After a quick visual, I switched it on with a silent prayer. A few pensive seconds later "viola" I was greeted with three green 0'S




I was stunned. These old devices are truly built like a tank, and they are a lasting tribute to the engineers and techs who designed and built them.

I was fortunate enough to get a great deal of the documentaion. The calculator was delivered in October of 1969 to a school district in California, and I acquired it in October of 2009. 40 years later it seems to be as good as the day it left the factory. I can imagine it lived a hard life among those students, but it never faultered in its mission.

In all my preliminary checks every operation seems to function. Unfortunately in came without the printer, but I did get the optical card reader accessory.

Now my problem. I have no media cards, so I cannot complete the checkout. No magnetic or card media came with the hardware.

Does anyone have any media to spare? I am not acually expecting to be successful with that plea. I know that "TAS" is a possibilty, but I finally broke that "bad habit" a few years ago, and that will be my absolute last resort.

I am always amazed at the number of bright and talented people who support this forum, and I thought perhaps someone had already blazed this trail before. Does anyone have any ideas about how to fabricate media cards for this device. This calculator "pre-dates" my desktop computing experience, I started out on an HP 9825. I have never even seen the type of media that I am searching for. With no samples or prior experience I don't know what I am trying to duplicate.

So if you have contributions, ideas, or suggestions I would really appreciate guidance.

BTW - product ID Z-000175 - no options stated


Don Williams


Lucky dog!


I can ship out a mag card or two. Let me know where to send them.



What a great offer. Could you please autograph them?

You can contact me at

Don W

Edited: 8 Oct 2009, 1:09 a.m.


Hi Donald,

I too stumbled on a HP9100A early this year, it was not working at first but the problem was just a couple of blown rectifying diodes in the power supply so I could fix it quite easily.

I wonder how many such units are still in working condition all around the world, may be forum could held a "census" about it ?

Also in my case I had the problem of missing magnetic cards so I tried to build some, at the end I made some working magnetic card for the HP9100A which I describe here below in case you would like to perform some test.

To start with I used the card dimensions, kindly told to me by a forum member (Etienne), to scale a printout of an actual card I found on the HP museum site.
I then glued it to a cardboard to reach the given thickness.
On the rear side I glued two strips of magnetic tape from a wrecked VCR cassette. Take care that the active side of the tape is that which faces outward w.r.t. the reels hubs, if you use the other side the support plastic film will prevent the head to get enough signal.
The exact position of the strips I derived from measurements of the head position in the card reader. It took me four tentatives to get a working prototype, I realized that the main problem are:

a) to have the correct width for the card (I found it is 50.5 mm) to fit exactly between the rails of the reader, otherwise the card tilts on the right when driven out by the mechanism (which has a single rubber wheel on the left side) and alignement is lost with the data.

b) to be very careful in having the tape smoothly glued on the cardboard, any wrinkle causes poor performances. The trick seems to glue the tape with the card slightly concave (U-shaped) so that when allowed to relax it will "pull" the tape flat. A quality check is that the tape surface must be reflecting an incident lightbeam as it would be a mirror.

I tried the card many times, at first recording a sequence of numbers (which is useful to check if the process "skips" a data) and later saving and reloading simple programs.

After the first success with short (20-30 lines) programs I tried to load on the calculator the full "diagnostic program" which is 196 lines long (i.e. the whole RAM capacity) which was used by HP field engineers to test the overall functionality of these machines.

The prime result was that my HP9100A passes the test, which is the final prove that the HW is all working.

I did some other experiments to find a reliable enough procedure to reconstruct cards which works, the point seems just to be very precise with dimensions and tape gluing.
On two of them I was able to load the full 196 steps sequence of the 9100A diagnostic program and the data were still retained one month later.

I have in the back of my mind the idea to write a "paper" about this topics to put in the related forum section but up to now I didn't fond the quiet times to prepare it, may be the renewed interest in HP9100 can trigger it.

Best Regards



Hi Paolo

I must apologize for my tardy response. Thanks for the information about fabricating a mag card. Some members have kindly offered to send me a sample, so hopefully I may have a specimen to copy soon.

Do you have a listing of the diagnotics program? I have just been randomly testing functions. It would be great to get a listing of the factory diagnostics. I have seen a missing digit on occasion. It must be intermittent. It would be helpful to loop the diagnotics for trouble shooting purposes.

Don W


Hi Donald,

you can find the listing in APPENDIX A of the HP Service Manual for models 9100A and 9100B H/P part 09100-90034.

you can download a copy of this document from the Australian site herebelow:

In this site there is lot of other good stuff, worths a visit.




Hi Paolo

I need to read my own documentation a little more carefully. DUH!

Thanks again for the info and the link.

Don W


What a fantastic stroke of luck! I am very happy for you, if not somewhat seething in envy! I don't consider my collection complete until I have a 9100 so your fortune gives me continued hope. Keep us posted of developments please. It is an amazing machine and I like to read user's experiences of them.


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