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TL;DR: The service manual for the HP-97 mentions a tool (T-155435) for removing/inserting the card-reader ribbon cable. My own cable, while seemingly still intact, has a number of the fingers lifting off the cable end, and if I insert it in this condition, I'll break some of them. Needless to say, I don't have this tool, nor have I ever seen one, not even a picture of it. Presumably some flat, thin, stiff piece of metal or plastic is inserted with the cable to cover the fingers, and then withdrawn. How do you take care of this problem when working on the card reader?


I bought this HP-97 for a song many years ago, and while the calculating part worked fine, the card reader didn't, and the printer is marginal (it can be made to work if one pulls straight up on the paper to stiffen it in lieu of a platen). After a while I pursued fixing the card reader, and of course it had the gummy-wheel problem. I put two O-rings on it, and cards went through the reader but always complained of Error.

Fast forward a few years until a few weeks ago when I was getting really tired of not being able to save programs and data to reload later, so I dug in again. I made the mistake of oiling the worm gear (presumably because it was stalling, due to the crumbling clutch), which dribbled on the O-rings, eliminating any traction a card may have had. I figured a little IPA would clear out the oil, and it may have, but it never evaporated from inside the card slot. A cotton swab made a half-hearted attempt to dry out the O-rings, but was not very successful. Meanwhile I set about redoing that clutch by replacing the crumbs with something (tried insulation, but I didn't have the right size. Tried silicone caulk with little success either). The silver-colored collar came off the worm gear shaft, so I put it back with superglue, and may have fixed it to the motor shaft the same way. I honestly don't remember exactly what I did there. I also decided that the O-rings were never going to dry out, so I went about replacing them with the rubber tubing that fits so well. Had to take the card reader apart, exposing the nylon balls and the leaf springs to their freedom. By some miracle I managed to find all the nylon balls every time they went walkabout, and almost every time the leaf springs did too. Those springs were very uncooperative at getting back where they belonged, would fall out when I turned that part over to mate it with the nylon balls, and one of them vanished completely. I searched for a substitute, having measured the remaining one at 5/64"x28/64". As it happens, the width of a magnetic card is almost exactly the length of the springs, so I sacrificed one (of my eighty blank ones I haven't managed to use yet) learning how to cut it that narrow. Made two that would fit, and they didn't fall out! And a card was drawn through when I powered the motor with a battery! So now I'm waiting to figure out how to reconnect the ribbon cable without destroying it.
A while back when working on a 97 I fabricated a cable removal tool. Using some 0.009 inch sheet metal from the local hobby shop, I cut a number of connector-with strips, then covered one side of one end with kapton tape (for the cable-side). Works great!

To insert the damaged cable, you might try wrapping some kapton tape over the end by a small amount, maybe 1/16 inch. The connector contacts are recessed a little so the kapton shouldn't interfere with the contacts.

It sounds like you had some fun trying to do repairs ;-)

I used some aluminium cut from a soft drink can and made sure there were no sharp edges, but any reasonably stiff plastic of similar thickness will do. The plastic from those cheap throw away plastic food containers will probably do. These also do to put the little parts in during disassembly. Placing a thick towel or similar on the work bench may stop the little parts bouncing into oblivion.

The HP-97 service manual page 4-16 shows the procedure.

Please do not try to pull the ribbon out without the "tool" or you will damage it.

You will probably have to open the card reader and do a proper clean for the oil.

I repaired the motor shaft coupler with the method described here and has been working ever since.


There are other methods, one from Geoff Quickfall

It is hard to say about card errors as there could be many reasons. If the reader is disassembled, try cleaning the head, check circuit boards for corrosion, check for broken wiring and connectors. Other tests probably require an oscilloscope.


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