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HP Forum Archive 15

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Card reader clutch repair
Message #1 Posted by David Ramsey on 30 Dec 2005, 8:25 p.m.

I've got a flakey HP-67 card reader that I think has a clutch problem. I repaired the gummy wheel on this reader a few years back using "O" rings. They look fine, but the reader has real problems pulling a card through-- terrible squeaking noises and jerky card movement. I have tried adjusting the drive wheel offset but it seems to make little difference.

The pitch of the motor jumps higher when the card slows or stops, which I attribute to clutch slippage.

The worm gear slides easily off the motor shaft. Apparently the "clutch" is a rubber or plastic material inside the worm gear shaft that provides a friction fit to the motor shaft.

The obvious solution is a drop of adhesive, but that would eliminate the "clutch" action. On the other hand, unless the reader mechanism jammed solid, would this hurt anything?

Suggestions on a reasonable repair appreciated...

Re: Card reader clutch repair
Message #2 Posted by Jon on 31 Dec 2005, 5:20 a.m.,
in response to message #1 by David Ramsey

I have got excellent results with small pieces of plastic tube (itīs brand name here in Spain is "Ibersil"). But I think that you can do it also with the plastic isolation of electrical wire.

some words about the so-called clutches...
Message #3 Posted by Hans Brueggemann [GER] on 31 Dec 2005, 8:05 a.m.,
in response to message #1 by David Ramsey

...of the card readers. following the many posts here in the forum that deal with card readers of 67 and 41 machines, you can find two major opinions about how the worm gear is attached to the drive motor. fact is, that the worm gear is simply pressed onto the motor shaft. the two opinions either state, that the attachment tube of the worm gear serves the extra function of protecting the card drive against too much torque, in case the card movement is blocked somehow. the other opinion is, that there simply isn't any purpose of the attachment tube other than attaching the worm gear to the motor in a fashion, that it can be dismantled and reused in case, say, of a motor fault. i'm of the same opinion. there is *no* protective function designed into the whole drive, other than the weak motor itself. you doubt? try the following: connect the motor to a proper power supply, start it up and try to block it with your bare hands. no bloodshed, though you might have expected that. the generated torque is so low, that there is not the slightest chance to damage anything inside the card reader if the card is blocked. furthermore, you simply won't find *any* card reader, that, with a stuck card, keeps the motor running (until shutdown) and, on the other hand, is able to properly drive a card through the reader. that's why i consider the "safety clutch" nothing more than an "urban legend". it is just an inexpensive means to connect a worm gear to a motor. that's it. just my two cents to the everlasting discussion about "loctite or gelee royal?" cheers, hans

Re: Card reader clutch repair
Message #4 Posted by David Smith on 31 Dec 2005, 11:44 a.m.,
in response to message #1 by David Ramsey

The motor shaft coupling is definitely NOT a clutch meant to slip. The HP97 service manual talks about reading the motor current with the card stalled by holding it.

The best adhesive that I have found is called IC2000 tire cement. It is a rubbery superglue for gluing tires to RC race cars. Get it at Hobbytown, etc.

Spin the motor shaft. Does it scream? Then oil the bearings with Breakfree CLP and a small paint brush. Wait 30 minutes.

Clean the motor shaft with alcohol and let dry. Paint the inside of the worm gear with a light coating of the glue (I use a small piano wire dipped in the stuff). Press on the worm gear all the way. Let dry for several hours. Reassemble the reader. Enjoy.

Note that if you used too much glue, the worm gear may not fully seat on the shaft. You may need to shim the motor with some thin plastic (pieces of an old mag card?) if the motor binds.

Also sometimes the nylon motor coupling breaks in half. If a small nylon piece somes out with the gear, you should also glue it in place to the gear first. If it crumbled up, use a piece of WD40 spray hose.

Re: Card reader clutch repair
Message #5 Posted by David Ramsey on 31 Dec 2005, 6:17 p.m.,
in response to message #4 by David Smith

Thanks to all who responded. I cleaned the motor shaft and applied a very tiny amount of cyanoacrylate (super glue). I slid the worm gear over the shaft and let it sit an hour. The card reader now works perfectly!

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