HP Forum Archive 08

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fix card reader Message #1 Posted by Jeff Glass on 6 Aug 2002, 3:18 p.m. 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

Re: fix card reader Message #2 Posted by Vieira, Luiz C. (Brazil) on 6 Aug 2002, 11:59 p.m., in response to message #1 by Jeff Glass 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.

Re: fix card reader Message #3 Posted by David Smith on 7 Aug 2002, 12:32 a.m., in response to message #1 by Jeff Glass 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).

Re: fix card reader Message #4 Posted by Andreas Müller (GER) on 7 Aug 2002, 4:57 p.m., in response to message #1 by Jeff Glass 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

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