HP 97 problems



Could someone help me?

I use an HP 97 calculator, and have problems with the cardreader: The reading is OK, the wheel is replaced but the writing brings error in the display!

So i want to make the capacitors on the cardreaderboard new, but i dont know the range and the type (tantalum, ...).

What should/can I do?
Many thanks in advance!



Check that both head windings are okay, 50 ohms between red/yellow and blue/orange. Be sure to clean the head well and check that the card detection switches are closing, you will get a write error if the write protect switch is not making contact. It is more likely to be a switch problem than a capacitor based on your problem, but, since you asked:

The small cap closest to the transistor is 6.8uf, the cap next to it and above the diode body is 3.3uf. The two next to the IC are 22uf each. The bypass cap across the motor should be replaced as well, it is 3.3uf.

The square pcb pads are +. All caps are tantalum, 10 volts.

Good luck.


Hello Randy, folks;

what is the "fucntion" associated with each head windings? I remember that there are two tracks on each side of a magnetic card, and I guess that one is a "sync" sequence (is it recorded everytime a card is recorded?) and the other is the very data sequence. Is it correct?

I'd like to know what sort of action is performed by each winding when reading and recording cards. I repaired some 82104A card readers but I never needed to follow the circuits and check if the head windings were O.K.

Thank you.

Luiz (Brazil)


For the 65, 67, 97 and 41, there are 2 tracks in each direction on the card. A magnetic transition on one track is a '0', a transition on the other track is a '1'. It's a simple self-clocking scheme. The same idea, BTW, is used for the tape cassettes on the 9830, with a transition on both tracks being an end-of-byte marker.

For the 71 and 75 I believe there's a timing track and a data track in each direction.

For the 9100, 9810, and I believe 9820, there are 4 tracks in each direction. 3 data tracks and a timing track. This suits the 6-bit keycodes used by the 9100 and 9810 (odd bits, even bits split, BTW!) but is less suitable for the 8 or 16 bit words of 9810 data or 9820 characters.


If it reads OK, then the head is fine, the capacitors are most likely fine too..
The problem could be due to the write-protect switch not making as the card goes through. so the 97 thinks the corner is clipped (I assume you're using an unclipped card!). You need to take the card reader apart, clean the contacts (rub them _gently_ with an ink eraser, then clean with propan-2-ol), then set them as documented in the service manual (on the MoHPC CD-ROM).
This is not hard to do, from what I remember you put a continuity tester between points on the card reader PCB, then screw in an asdjusting screw until the contact just closes, then unscrew 1/8 of a turn.


Thanks to all the posters, my problems are solved!

The mayor problem was the write-protect-switch!
(Other problems: the wheel and massive dirt)

I've testet last night about 200 mag-cards, no drop out!!!!!

Remember: the machine is 25 year old!



You may find that in a few weeks you need to adjust one or more of the reader switches again. The adjustments tend to interact with each other and occasionally "drift" after being adjusted.


Thank you!

It seems, that you play a lot around with this machine ...



Way too much...


I had that problem (drifting adjustments) in the '97 from hell' -- an HP97 I was given with just about every known fault and then some!. It got to the point that I could set them up, and they'd not work next morning.

In the end I took the reader apart and _really_ cleaned the contacts (rubbed them with an ink eraser, then with propan-2-ol). Put it back together and made sure the fixing screws for the leaf contact (the 2 at the end) and the PCB were properly tightened. It was OK after that.


I fixed one particular HP97 from hell by putting it at the bottom of a bore hole that was then filled with 10,000 lbs of blasting agent (adjacent with several hundred other similar holes)... no more problems with THAT machine have been reported.


Oh Dear! You shouldn't do that. You're likely to scratch the display.



And presumably no results either ;-)

Anyway, in the case of my 97 it almost became a matter of honour to fix it. I was not going to be beaten by a darn calculator (actually, I am not going to be beaten by faults in any electronic or mechanical device, but I digress). The fact that this had more faults than is reasonable is irrelevant -- dirty keyboard contacts, dirty card reader contacts, decayed roller in the card reader, printer feed roller not gripping properly, paper feed switch wires needed resoldering, dead ACT chip, battery contacts broken away from the chassis, etc, etc, etc.

Oh well, I _did_ fix it in the end...


Men and there toys....

Me too ;)



Ahhh, all the ususal suspects. My unit had about all of those plus poltergeist, oozing ectoplasm, foul smells, rattling chains, loud moaning and screams etc. Any fix unfixed itself and then more problems showed up. Nevermore...

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