Time ago I posted here a question about repairing a HP-67 card reader. It had the known problem of these readers. It records ok but fails when reading (not always).
Somebody recommended me to change a tantalum capacitor. I have opened the calculator to do it and... BAD LUCK!!!!.

It is an early version of the reader with three cylindrical silver capacitors on the board.

Does anybody have experience with these models?

Thanks in advance



I am in process of repairing the reader on my HP-65 and my next project is to replace the rubber wheel on my HP-67 card reader.
The readers are very similar. Those tantalun capacitors located on the narrow piggy back board are decoupling caps for power supply. Now how can you verify that you can record a program if you can't read it?
Since you opned your calculator I recommend you demagnetize the R/W head.


It records ok all the times. I have an HP-97 so I can check it. The problem is that in early versions of the HP-67 there aren´t tantalum capacitors. They are cilindrical, with silver surface (they don´t look like electrolitics).

How can I demagnetize the head?


Hi, Jon;

I saw many of these capacitors in earlier Woodstocks, too, if we are talking about the same components. I have two of them in hands right now and I read:


150D ±10%

I used to take them all as electrolytic capacitors, maybe the ones you see are not. Have you checked for their values? Just for checking.

As you may know, tantalum are polarized, have higher internal resistance and do not show value drift easily. In some applications, tantalum are better than electrolytic.


Luiz C. Vieira - Brazil

Edited: 1 June 2003, 11:03 a.m.



Thanks for the fast answer. I have also seen those capacitors in woodstock calculators. The problem is the caps of the HP-67 are much more smaller and I can´t read any value. May be I try to unsolder all of them, measure the value and change for electrolitic or tantalum caps.

If I get any success I will make you know.



I don't think your HP-67 is older than my HP-65. The cylindrical caps are tantalum (it does't make any difference tantalum or elctytic both types are polrized)
I bought a demagnetizer from Radio Shack P/N 28-07246 it is called HEAD DEMAGNETIZER I used to use it on my cassette recorder heads. Demagnetizing could help the cause but it could be somthing else wrong.
You can send me an email to my yahoo addresse. Here is a link with som pictures showing the inside of HP-67.


Those cylindrical silver caps are tantalum caps... they are just in a much more expensive package than the dipped epoxy coated ones. They also are much more reliable. I don't know which of the three is the power supply cap, but two of them are connected to the head circuitry (see the HP97 service manual on the HPMUSEUM CDROM set).


Hi, folks;

Despite of size and external structure, are readers the same for both HP97 and HP67? I do not have any of them (so far; I'm about to receive a gifted HP97; thanks D.S.!) and I'd like to know what from one card reader corresponds to the other in the same way and what doesn't.

I remember seeing pictures of the HP67 reader internals (MoHPC? I don't remember) and there are some structures that "resemble" the HP82104A equivalents (HP41's Card Reader). What called my attention at that time was the HP67's one-piece card sensor metal plate, because there are two independent metal plates in the HP41's card reader.

I'm aware of PCBs' design, structural components and their differences because both calculators have different cases and internal space. What I want to know is: knowing about one's internals will help repairing the other? I think this is my biggest question.

Thanks for any information.

Luiz C. Vieira - Brazil

Edited: 1 June 2003, 5:44 p.m.


The reader electronics for the HP67 and HP97 are similar. The HP97 has a different power supply arrangement for its reader. The sense amp chip and head wiring is the same.

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