Hewlett Packard

Classic Calculator Gummy Wheel Repair
Fits the HP-65, 67, and 97

Model: Gummy

Why doesn't my beloved calculator push through the magnetic card?

Mainly because the original rubber o-rings have decayed since the 1970s and either has hardened into a mess or gotten soft and "gummy" leaving a sticky residue when you push through a card (if it advances at all). The good news is that you can fix it, but you need the materials provided here.

I've repaired dozens of these classic calculators and have written articles in the HP Calculator Museum website on how to fix this problem. Other have written since then (2002) excellent guidance tips.

I'll send you links to PDFS on how to repair the HP-65, HP-67, HP-97 and 41C Readers

Go slow, be careful. I have some parts, if some of the little buggers "fly away". If the calculator look very good, you have a very good chance of fixing it. If there is significant corrosion, that can be a challenge, but don't give up. Give it a try. I would be glad to also fix it for you if you'd like, just let me know. I typically charge around $30 and shipping, only $10 (in USA shipping) if I fail. If it is hopeless, :( no charge... except to ship it back to you.

You will receive O-rings. I'm not convinced that the tubing works all that well. I strongly feel the O-rings work best. Other feel that the flat-area of the tubing is better to move the cards. Historically most all my repairs are Orings. I feel that the even geometry of the Orings is to your advantage.

Here is a big tip. After replacing the Oring, before you close the calculator try to gently push a card to see how tight the Orings may impact the card. It should be snug, but not too snug. You can also try to use 3 volts on the motor to see how it pulls the card through the reader. The "snuggness" should be minimal, if you have to push hard then reset the Orings, looking for a slightly smaller Oring. They vary a little as you will see. If the motor pull s the card nicely, you should be fine.

The capacitor can be a big difference. Notice on the internal photo (upper right) that I installed it in reverse so that it fits better. Note that the capacitor has polarity, the marked terminal is to the left (see picture). Some of the HP Forum electronics experts feel that the weak link is this capacitor. Another thing I have noticed recently is the need to very lightly sand the long connecting ("Bridge") board. If there is corrosion sanding it removes it a bit and makes the circuit work better. A new thing I do now.

Shipping: Shipping costs are listed below. For multiple battery pack purchases contact me for actual shipping costs. I will only charge you actual shipping costs. BTW, 93.9% of my sales are mailed in one day.

Also check my other HP calculator battery packs for sale especially for the Spice HP 33-34-35 calculators and for the larger HP 95-97 calculators.

Hope to add you to my list of satisfied customers.

Sincerely, Mark Hoskins

Gummy Wheel Repair Hewlett Packard Calculator HP-65, 67, and HP-97

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