HP 97 card reader



#15

Hi all,

I picked up an "untested" HP97 on Ebay, and have just finished cleaning it up. It had an "old electronics" smell, and was loaded with insect droppings and some insect parts. I disassembled it down to the last screw and thoroughly cleaned it. I am powering it via a 5V supply to the terminals (thanks Dave for including the polarity in your pics on the battery page!)

So far, The calculator works beautifully, and I can advance paper, but have to buy some calc paper to test the printer out. During the cleaning, I repaired the gummy card reader wheel, and removed all the gunk (mixed with bug parts and droppings--ugh.) Now, when I insert a card, there is no response, but when I push the card far enough, I get an ERROR message on the display. I am unfamiliar with the apparatus, but would guess it's either a motor or card sensor problem. I did remove the little foil spring contact on the reader, which I am guessing is the sensor for card progress through the slot. It has four little balls and 5 screws, three of which are accessible with the assembly cover in place. Am I right in guessing that there is a proper process for setting the tension on the foil via those screws, and that I probably messed it up when I disassembled it? Any suggestions on what might be happening?

I have read the prior posts, and understand that sometimes some of the caps on the assembly cause problems. However, I hate to just start replacing parts without knowing for sure what is wrong. I used to have the DVD with all the manuals, but can't find it anywhere. I just ordered a new set, but it looks like I won't have this before the holidays:-( So anything that might point me in the right direction would be most appreciated!

For those celebrating Thanksgiving, have a great holiday!

Dave


#16

Also, can I work with the unit with the keyboard off? In otherwords, suppose I wanted to try adjusting the tension on the card sensor foil. Can the processor operate and respond without the keyboard attached? My idea was to start gently adjusting the tension, and see if the card gets detected at some point (hopefully the processor would activate the motor); otherwise, I will try to open up the unit, trace out the circuit, and then check the voltage at the switch, and turn the screw until the switch trips on card insertion.

Am I thinking in the right direction? These parts seem pretty delicate, and I'd hate to needlessly damage something. I'm fine with electrical stuff, but as someone who can't build a square picture frame, if I break a mechanical part, I'll be looking for another "untested" HP on Ebay. . .

Dave


#17

First, those are leaf switches, not springs, and they are not tensioned. They work by the card depressing the balls, which press on the tips of the switches, causing them to close the circuits by pressing them against the circuit board. One of the switches causes the motor to start when it is closed. They can be adjusted, but it's tricky, and generally not necessary. According to the HP 97 service manual: "If any of the switch contacts are bent, replace the leaf switch contacts rather than attempting to bend them into position."

Second, are you sure you got all the little parts in place when you reassembled the card reader ? You mentioned the 4 nylon balls, but there should also be a nylon pinch roller and two curved brass spring guides as well.

Third, the easiest way to check out the card reader is to remove the entire assembly including the ribbon connector from the calculator, and apply power directly to its terminals. This way you can isolate the issue to the motor or switches. If the reader checks out outside the calculator, then the problem is in the calculator itself.

Edited: 21 Nov 2011, 1:37 p.m.


#18

Thanks for the reply.

I was able to get the machine to detect a card; I can hear the motor running but the card isn't being pulled through. There's a lot of resistance.

Regarding the little parts, they are all there, but the roller did not turn particularly freely. I'm wondering if that's not part of the problem. Should that be turning pretty freely? If so, does it need to be lubed somehow?

Best regards,

Dave.


#19

The resistance is usually related to a larger than necessary roller tubing or O-Rings. Try to decrease the diameter a bit with the help of a Dremel tool and a nail file.

A more fearless approuch:

- cut a piece of a nail file large enough to fit freely inside the roller chamber

- connect some alkaline batteries to the motor terminals

- file the roller

- clean

If the problem remains, verify if the clutch is working good. The cause may be there...


#20

Thanks for the suggestions. I think the roller is OK. I had some silicone tubing that was almost the exact diameter of the metal part of the roller when placed. With power off and motor removed, I can slid a card through.

However, I had not been aware of a clutch mechanism (although I see there is an article about it.) I just looked at the clutch as you suggested, and the plastic stuff fell out, so perhaps that is a part of the problem. I will review the article about repairing the clutch, and see if that helps.

Best regards,

Dave


#21

It's actually not a "clutch", but just a flexible connector between the motor and worm gear that is not supposed to slip. However, the "clutch" term has been used a lot, so many people call it that. Remove it and save the metal collar, then find some wire insulation that is a tight fit inside it. The ID of the insulation must be a tight fit on the motor shaft that can be secured with a drop of superglue. The other end must be bored out sufficiently to fit the end of the worm gear inside it until it bottoms out on the end of the motor shaft. I've used a heated nail to bore it by melting the insulation. So far I've succeeded with this method on 3 card readers.

#22

One possibility is that the motor shaft is slipping in the elastomeric coupling (aka clutch) and the worm gear is not turning. The coupling is made of a material similar to the drive wheel that deteriorates over time. If that's the case, you will need to rebuild the coupling. I have succeeded in making this repair using wire insulation. Again, you can see this if you remove the reader assembly from the calculator.

Also, you may not have the drive wheel adjusted properly. The shaft is eccentric, and can be adjusted to provide more or less pressure on the card. The recommended method in the service manual is to measure motor current at 180 +/- 20 mA when it attempts to pull a card through but is not allowed to.

#23

On further examination, one of the spindles of the pinch roller is thicker than the other. The smaller side drops easily into either slot. The thicker side needs to be pushed to fit, in either orientation. This is preventing the roller from moving. I am guessing that the spindles should be small enough on both sides to drop in and roll freely.

Any suggestions on how to fix this? I am thinking emery board, but I'm going to wait a bit, because when it comes to mechanical fixes, I always end up wishing I'd waited and gotten some advice :-)

Dave


#24

A normal pinch roller fits easily into the slots, and is the same on both sides. You may have a home-made substitute of some kind.


#25

It doesn't look homemade. The thicker spindle is slightly bulbous at the end, almost as if it has melted.

Examining the clutch on my unit, the aluminum sleeve is very firmly attached to the worm gear, extending in about 1/2 the length of the sleeve. There is a hole at the end of the worm gear into which the motor shaft fits without any friction, so the gear/sleeve assembly fits over the motor shaft. So this appears as if it was designed to slip above a certain torque.

So, the plan is, based on advice here, and the various articles,

1) file down that spindle until is falls easily into the slot)

2) Replace the "clutch" material, which has dried and crumbled away. Insulation for 18 Ga wire fits well over the motor shaft, so I'll dip the insulation in silicone compound, and place it in the aluminum sleeve, using an 18G wire to center the insulation relative to the worm gear. Then I'll remove the wire, cut off the excess insulation, and slip the whole gear/tube/insulation assembly on the motor.


#26

Quote:
So this appears as if it was designed to slip above a certain torque.

That was what I thought, too, but in fact this is not the case. The motor / coupling / wormgear was supplied as an assembly by HP as p/n 00067-60904 and no slippage was intended. The remaining coupling material will continue to deteriorate and the slippage problem will return unless you remove all of it and replace it with new material.

#27

Quote:
Also, can I work with the unit with the keyboard off? In otherwords, suppose I wanted to try adjusting the tension on the card sensor foil. Can the processor operate and respond without the keyboard attached?


Nope - but this thread shows another approach, and gives some excellent guidance on repair and adjustment.

Cheers,
Bob


#28

Thanks Bob,

That's a great article. I'll flip the reader over as shown so I can test it in circuit. It will probably be the holidays before I can spend more time with it, though.

Dave

Edited: 21 Nov 2011, 8:26 p.m.


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