HP-67 Card Reader Motor

[Stefan Vorkoetter]

About a year ago, I purchased a never-repaired HP-67, knowing full well that it would have gummy wheel syndrome. Yesterday, I proceeded to go fix it, using the appropriate sized O-rings. (The previous day, I had similarly repaired a pair of HP-41C card readers.)

Everything went well, but after I put it all back together, it didn't work. Inserting a card would cause the motor to run very briefly (perhaps two or three turns of the worm gear), and then stop. The calculator would display "Error". Although I can't be sure, it sounded like the motor was straining somewhat. For what it's worth, before the repair, the motor ran as expected when a card was inserted, although the card wasn't pulled through due to the gummy wheel.

I plan to redisassemble the unit tomorrow to try to figure out what the problem might be, but thought I'd ask a couple of questions in case anyone has run into this issue before.

1) Has anyone seen a case of the motor itself actually being no good any more on one of these calculators?

2) If so, is the motor from the HP-41C card reader identical?

3) I haven't yet rebuilt the battery, so the calculator was running from its adapter (which supplies regulated power to the 67, unlike some of the newer calculators where the battery acts as the regulator). Does the adapter provide enough current to run the card reader?

Thanks in advance for any info or insight you might provide.

Stefan Vorkoetter

http://www.stefanv.com/calculators

[Randy Sloyer]

See answer #3 first!

1) No
2) Yes
3) No

And damage to the card reader sense amplifier is possible under the conditions you describe. The 65 and 67 MUST have a good battery in place when connected to the charger. It's in the manual :)

[Geoff Quickfall]

Hello Stefan,

I have repaired several of these calculators including Namir's 65 and 67 as recently as yesterday!

NO! the adapter does not supply the correct current to run the card reader separately. You must have good rechargeables in the calculator,

OR

Once I have the pinch roller and clutch replaced; always replace the clutch with the pinch roller as, in time it WILL fail once the pinch roller has been replaced.

With the rear shell removed, I apply a three volt current to the motor contacts with a card in place to confirm the card will travel

OR

place a battery pack in the holder of the calculator insuring the gold clip is in place at the adapter contacts

OR

using an external battery pack and clips apply the clips to the contacts in the battery holder of the calc observing the correct polarity (see picture and by the way, use nicads not alkalines as I did in the picture!)

REMEMBER, the white axle has an assymetric fitting on the pointy end of it, this is used to raise or lower the pinch roller to allow the card to be pressed correctly against the card reader head. For example, after fitting the new pinch roller in Namir's hp 65 I kept getting error on about 80% of the card passes. By adjusting the axle with the rear shell off, using the slot in the end of the axle I raised the pinch roller enough to have 100% reliablitiy on the read and write function.

In conclusion,

1. if you don't have a battery pack, make one as pictured using nicads!

2. you can check the motor function by applying 3v to the motor contacts.

3. adjust the pinch roller height with the white axle by turning the axle using the slot for applying the twisting moment. I bent a screw drive tip 90' to allow access to the axle when the slot is hidden by it's orientation.

Good luck.

Geoff

Edited: 12 Nov 2008, 11:21 a.m.

[Stefan Vorkoetter]

Thanks for all the input guys. That gives me something to work with. I wasn't aware that the roller axle was asymetrical. That explains why one of my 41C card readers sounds like it's having an easier time of it than the other.

Regarding the power adapter, I was under the impression that of three terminals, one was ground, one was a regulated +5V to operate the calculator, and the third was an unregulated low current supply to charge the battery. Is it the case that the card reader gets its power from the unregulated side, meaning that it isn't getting proper power unless a battery is installed?

I hope I haven't damaged the card reader circuitry. :-(

I guess I'll find out tomorrow.

Stefan

[Stefan Vorkoetter]

Well, I couldn't wait until tomorrow, so I built a new battery pack this evening, charged it for a few hours, and gave the card reader a try. It works! Phew!

Regarding the setting of the axle to adjust the wheel pressure, how does one determine the "correct" setting? Is there some specific amount of current the motor should draw while pulling a card?

Thanks again,

Stefan

[Randy Sloyer]

The procedure is documented in the 97 service manual. 180ma +/- 20ma when holding the card (stalled).

[Stefan Vorkoetter]

Are you sure this is the procedure for setting the roller pressure? When the motor is stalled, the roller pressure won't matter, unless the roller is slipping (in which case the motor isn't stalled).

Stefan

[Randy Sloyer]

Quote:

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Are you sure this is the procedure for setting the roller pressure?

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Then read the 97 manual if you don't believe me... I never said the motor was stalled, only the card.