Cleaning the goo off card reader



#8

What's a good solvent for cleaning the gooey rubber off the HP 97 card reader parts? Acetone? DesolveIt?


#9

I decided to try acetone. It disolves the goo just fine, but I'm worried it might attack the plastic parts too. So far, I've used it only on the steel shaft that carries the rubber roller.

If anybody has a better idea, let me know.


#10

Alcohol or rubbing alcohol (anhydrous propynol, iso-propynol). I use 99% and you can find it at the drug store. Acetone hates plastic and if you get some on the pinch roller plastic you will ruin the teeth.

In fact alcohol will remove the goo from the card reader frame work and not affect any of the plastic. Use a stif natural bristle brush and clean the eccentric cam, pinch roller, framework.

Your next step is to decide on which type of pinch roller rubber substitute you will use, silicone tubing or o-rings.

Also, once the pinch roller is cleaned and the rubber replaced the next fault area is the dampening couple (incorrectly refered to as the motor clutch). It is the tiny aluminum sleeve connecting the motor shaft to the worm gear.

It is made of the same rubber and suffers the same degradation as the pinch roller. While you are at this point you might as well replace the rubber there also otherwise the rotational stress of the new pinchroller system will cause it to fail.

Cheers, Geoff


#11

Quote:
Alcohol or rubbing alcohol (anhydrous propynol, iso-propynol). I use 99% and you can find it at the drug store. Acetone hates plastic and if you get some on the pinch roller plastic you will ruin the teeth.

Good thing I asked!
The Rubbing alcohol on the shelf is 70%. Will that do?

Quote:
Your next step is to decide on which type of pinch roller rubber substitute you will use, silicone tubing or o-rings.


I bought the O-rings from the eBay seller of same. Seemed easier than looking for a model airplane store or a medical supplier, the apparent sources of other suggested replacements.
Quote:
Also, once the pinch roller is cleaned and the rubber replaced the next fault area is the dampening couple (incorrectly refered to as the motor clutch). It is the tiny aluminum sleeve connecting the motor shaft to the worm gear.

It is made of the same rubber and suffers the same degradation as the pinch roller. While you are at this point you might as well replace the rubber there also otherwise the rotational stress of the new pinchroller system will cause it to fail.


So I have to remove the motor, pull the sleeve/worm gear off, and dig the goo out of that tiny aluminum tube? What is the replacement?
[/quote]

Thanks!


#12

70% works fine, nice thing is that the alcohol will evaporate. I use it to clean the pcas and contact points. Good for the card reader head, similar to the cassette deck cleaners we used with cassettes.

here are some photos of the dampening couple. I use two different diameter wire insulations to simulate the rubber of the original couple. remove the wires and insert the small diameter into the larger diameter. the smaller diameter will be shorter allowing the wide diameter to connect to the worm gear and the narrow diameter to connect to the spindle of the motor:

a: spindle
b: aluminum sleeve of couple
c: couple (deteriorated rubber)
d: worm gear

inset showing relationship of inner to outer insulation

assembled unit

I find this preserves the intent of the couple; to dampen the vibration between the motor and the worm gear.

I never tire of showing the following image of a deteriorated pinch roller from an HP-41C

cheers, Geoff

Edited: 12 Mar 2010, 11:25 p.m.


#13

Thanks, Goeff.

A couple more questions.

How do I tell if my dampening coupler needs to be fixed?

In the original part, was th pliable material bonded or glued to the sleeve and shaft? What I'm getting at is whether slipage is indended, or the action of a dampened spring?

Finally, do you recall the wire sizes?


#14

"How do I tell if my dampening coupler needs to be fixed?"

Because it is there ;-) Really because it is the same material as the pinch roller and age and you might as well repair it at the same time that you have it apart for the pinch roller. It saves flexing the solder joints and wires.

"In the original part, was th pliable material bonded or glued to the sleeve and shaft? What I'm getting at is whether slipage is indended, or the action of a dampened spring?"

It is compression and friction fit, no glue, that is why gluing or adding cyano acrylate as some suggest is not the best fix, although it works.

"Finally, do you recall the wire sizes?"

Not off hand and I am not at home to refer to my notes, but get the larger diameter with a slightly larger outer diameter then the aluminum sleeve and the narrow insulation should have an inner diameter smaller then the motor shaft for a friction fit. You nmight have to experiment.

Cheers, Geoff


#15

Shrinking tube is another material suitable to fix the coupler.


#16

Hello Marcus,

I have heard this before and was wondering if you have had first hand experience with it.

Do you remove the aluminum sleeve and just join the shaft and worm gear together with the heat shrink tube?

Or do you fit it then slide the aluminum tube over the repair. If so do you equalize the diameter of the tubing on the narrow part to equal the thickness of the tubing over the worm shaft.

Cheers, Geoff


#17

I did it just once for my 41 card reader. I think its just the tube without the metal sleeve. You need tube with the right "shrinking factor" because the ends are of different diameter. When I find the time, I'll open the case and check again.


#18

I don't see any mention of heat shrink in Geoff's method. Seems to be just ordinary insulation pulled off of solid wire.

Edited: 15 Mar 2010, 12:28 p.m.


#19

Never used the heat shrink method. I will check it out as an addendum to my HP 41C card reader chapter.

I have used the wire insulation method, but if the heat shrink works, and obviously it does, I will try it and document it.

Just recieved a box of HP 41cv cx and c boards shells and etc. Five in all and they all test even thought they have bad posts and shell washers. Looks like all five will be working when assembled and the shells repaired.

Also included was a card reader. All this for 122 USd:

2 HP 41C boards and one case(both boards test working)
3 HP 41CV boards and 3 cases (two boards test ok)
1 HP 41CX board and case (also tests ok)
1 HP 41 card reader disassembled in part (repairable)

Not a bad haul and as I stated, I will try the shrink wrap method on this card reader. The test will be to see how the hard shrink wrap dampens the vibration.

Cheers, Geoff

Edited: 15 Mar 2010, 3:07 p.m.


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