This isn't really an electronics repair problem. It might be better solved on an HP calculator discussion group, if anyone knows the whereabouts of a decent one.
I have a card reader for an HP-41C calculator (an HP 82104A). I took it out of storage (a zip lock bag kept in a desk drawer) the other day and plugged it in. When I fed a card through it, the card jammed and, when I pulled it out, it had a streak of sticky goo on it. So I disassembled the reader.
It appears that the little rubber(?) wheel that feeds cards through (driven by a motor and worm gear) has decomposed into the aforementioned sticky goo. What were these things made out of? What would cause them to decompose like this? Moisture? How much could there be in a sealed zip lock bag? What would be a suitable material to use to fashion a new wheel (about 3/8" diam by 1/8" wide).
Paul Hovnanian email@example.com
The wrong compound. Back in '87, my GF had a very expensive B&O stereo setup. Paid aTon for these "top drawer quality" components. After 3 years of little use, , the turntable made a scraping sound. I took it apart, and found the rubber bushings the drive motor was mounted in had deformed from the minute tension of the belt. The drive cog was running against the motor bracket. B&O said "tough bananas".Some quality. A friend of mine had a 3 yr old Range Rover. The dash material cracked and split Badly in this time. RR refused to warranty it. Sheesh. JR
Most "electronic" repair is nothing to do with electronics, its failed solder/connections/corrosion/failed rubber. Has anyone ever seen an only partly perished to goo, rubber part? no always total. Not only that but if one piece has failed then mre than likely others have failed inside the same kit. What is the contagion that passes between,? a gas? atmospheric contaminant?. I've got a box of salvaged rubber belts , and poured a load of talcum powder in there and stirred about. None have since perished, perhaps an interesting pointer to what is going on, but I still don't know what.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I was thinking originally that you might be able to rework the tyre from a cassette machine pinch roller, but silicone rubber tubing might be a viable alternative. I have used this for all sorts of little mechanical jobs like this, and it seems to be pretty resiliant mechanically, and resistant to chemical breakdown. I have it in several sizes that came to me from a coffee machine outfit that I repair control boards for. It is semi-clear food grade. If you have any trouble finding a source for a small amount, the vending machine industry might be a good place to look.
I collect HP calculators. Good sites to ask such questions are:
Ummm.... the 82104A is the model number of the card strip reader.
Yep. It's a common problem. The rubber breaks down and turns to incredibly sticky goo. I've repaired several HP65 calculators with a similar problem:
Note the photo of the drive roller.
It's actually a piece of hardware store vinyl tubing, carefully cut to length with a razor blade or surgical scalpel. (An Xacto knife is not sharp enough). I impaled a piece of tubing on a metal rod that fit the center hole, stuffed it into a drill press running at the slowest possible speed, and carefully cut pieces to length with a razor. There are probably better ways to do this, but I only needed one roller and didn't mind destroying a few more in order to get one that was perfect.
I've had zero luck with the o-ring replacement, which tends to slip because of insufficient contact area. I also lightly sandpapered the surface of the vinyl tubing in order to prevent slipping. I'm not sure if this was really necessary, but it can't hurt. Just remove the glaze and don't gouge the surface. It's easiest to do lengthwise along the tubing when skewered by a metal rod before cutting to length.
I also have in front of me an HP41CX with the card reader module. The internal construction is similar to the HP65. I haven't found the need to repair any yet so I have no experience with these. Here's a web site with photos and instructions:
It looks very similar to the HP-65 so I suspect that the vinyl tubing replacement should work. If you take it apart, be sure *NOT* to lose the tiny plastic balls sandwitched inside the reader mechanism. I've spent hours on the floor looking for where I dropped them.
I don't want to speculate on the cause of the rubber deterioration.
Jeff Liebermann firstname.lastname@example.org
150 Felker St #D http://www.LearnByDestroying.com
I had a similar problem with an HP flat-bed plotter. The pressure "tires" for the forward-and-back paper motion had failed while the plotter was in long-term storage... the rubber had become gummy, and had developed a bad dent on one side where they had been pressing against the motor-operated drive wheels.
From looking at them, I'd guess that they were composed of a synthetic rubber of some sort (I have no idea which formulation) and that the deterioration could have been due to long-term ozone exposure. Zip-lock bags are not, I think, proof against long-term diffusion of either moisture or ozone.
The parts are, of course, completely unobtanium at this point... the plotter is long past its end-of-life date.
I found that the tires had actually been molded onto the bearing (which has small ribs in it which engaged the rubber). I cut and scraped the rubber off of the bearing.
Molding on a new rubber layer didn't seem terribly feasible. However, at a local modeling-and-crafts store I found an acceptable substitute... a soft, flexible tubing made of a translucent blue silicone rubber of some sort, intended for use as a fuel line on radio-controlled airplanes. I was told that it's highly stable stuff, not attacked by volatile RC motor fuel.
I bought a foot of the right-diameter stuff, cut a piece for each bearing, and squeezed the bearing inside. Instant "tire" - perhaps not quite as perfectly circular as the original, but close enough that the plotter now works fine.
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
Defective. I checked the tubing I bought for concentricity and it was perfect. Having a variable wall thickness means the tubing is junk.
It won't matter much because you're only cutting off a very small piece. If it bothers you, impale it with a suitable stiff rod and hit it with a heat gun. It should straighten out.
Well, I don't know about the different formulations. I wanted something that was both the right size, reasonably hard, and fairly compressible in order to get a large enough contact area with the magnetic strip. Rubber chemistry hose was too soft. Rubber automotive gas line hose was too hard. Some other strange rubber tubing I found would take a compression set, which would cause erratic motionn due to the flat spot. Only clear vinyl tubing didn't have these problems.
Oops. The HP65 certainly has a few plastic balls inside, but maybe the HP41C does not. Dunno.
Here's another thought, Paul. I recently had to replace the fuel line on my garden lawnmower, and the replacement stuff that I got had a small bore, and a thick rubber wall which, without actually measuring it, looks to be pretty even for thickness
Yep. Junk. The error in concentricity is visible with a cheap magnifying glass. I found another hobby shop and picked up a foot of silicone tubing (the stuff they sell for model a/p fuel lines). It looked good and works fine.
Getting a concentric wheel on the mag card drive is critical. A bump a few thousandths too high and the added friction slows the drive down enough to cause a read error. A few thousanths too low and the card slips.
My initial try with the new tubing appeared not to work (jerky card feed). But when I took a close look at my new wheel, I could see that I hadn't cut the end of the tubing exactly square. So when I slid it against the little shoulder on the axle, one side of the tubing was compressed more than the other and, as a result, ushed up as a high spot. I just slid it back off the shoulder a few thousanths of an inch and it works just fine now.
None that I saw. But there's enough little springs and things that the advice still applies. One the goo is cleaned out of the reader, the two halves and a curcuit card don't need to be disassembed on the HP 41C reader anymore. The drive wheel is acessible from one side. So, as long as the new wheel doesn't decompose and its remaons need to be cleared, a subsequent wheel replacement will be pretty simple.
Paul Hovnanian mailto:Paul@Hovnanian.com
I don't think it will stay that way. It's going to move back and forth along the shaft. As I vaguely recall, the ID the vinyl tubing I used was just a bit too large for a snug fit on the shaft. I had to glue is with some kind of rubber cement to keep it from sliding and spinning.
I did quite a bit of tinkering in order to get the tubing cut squarely and the right size. I shoved a metal skewer down the center and spun the tubing in a drill press at the slowest possible speed. I used a razor blade or scalpel to cut it square. An Xacto knife was not sharp enough. I also broke the sharp edge of the tubing to prevent lumps.
I didn't have any probem with jerky feeds or errors with the replacement roller. The trick was to deglaze the surface. You shouldn't have to do that with a rubber tube, unless it's shiny.
Thanks. I anticipate doing the same thing to my HP41CX eventually. Good to know that it's easier than the HP65.
Jeff Liebermann email@example.com
150 Felker St #D http://www.LearnByDestroying.com
Hello, and I would just add that this was also a common problem (after a number of years of use) on the Texas Instruments TI-59 calculator. Happened to me. I guess after 30 years of just occasional use things start to decompose (just like with people). There was a fellow offering a TI-59 card reader repair kit on flea-bay consisting of a replacement (nylon?) wheel and a CD ROM with instructions. Perhaps a rubber faucet washer close in size could be reshaped to provide the correct inside/outside diameter. Hadn't previously heard of this problem on vintage HP card reading/writing calculators, though. Sincerely,
John Wood (Code 5550) e-mail: firstname.lastname@example.org Naval Research Laboratory
4555 Overlook Avenue, SW Washington, DC 20375-5337