fix card reader

[Jeff Glass]

Hello:
I have a card reader for the HP-41 that has the age old symptom of depositing sticky crud on program cards that I try to read. I then took it apart and cleaned it up and replaced the gummy glob with O-rings. Now, the cards run through there just fine. The first two cards I ran through, it read the programs into memory and they ran fine. Now the problem is, whatever card I run through, I get a checksum error. This reader seems to be writing to the cards because they can be read on a good reader. I know the cards I have are good because they read fine on a known-good reader.

I'm a pretty good bench tech and I fix things for a living. I've never fixed a card reader before, and I need some help and advice. If you know of someone that could fix this thing, please let me know that, too.

I'm new to this forum so I do not know for sure how to receive responses to this messsage. Please email me directly.

Thank you very much,

Jeff Glass, BSEE
xmitters@aol.com

[Vieira, Luiz C. (Brazil)]

Hello, Jeff.

I believe you'll find your answers here, and you can also try this one.

Success! Let us know about your card reader.

[David Smith]

A card reader that writes but will not read is almost always caused by a defective tantalum bypass capacitor on the sense amp chip. There are two in the head coil circuit... no problem there. The one on the power supply to the chip develops a high ESR and voila... no el reado. It is almost always a small blue dipped tantalum with around a 4.7uF value (not particularly critical).

[Andreas Müller (GER)]

And in addition to Vieira's advice look here http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cgi?read=20310
Did you use demagnatized screwdrivers? Did you demagnetize all the screws?
This solved most of my problems with card readers.
Regards, Andreas