HP-67 Repair Success!


Thanks to all who replied to my "Waterlogged HP-67" post and offered suggestions for proceeding, as well as to the countless posters and authors of repair articles on the MoHPC. I took the "easy" way out and used Formula 409 to clean the inside of the case, the keys, and the circuit boards as well. There was no major visual damage... just some minor discoloration possibly due to the soft drink that had never been cleaned off. The battery pack had no visual corrosion or leakage and had a slight voltage charge still on it (after 13 years!) After reassembling the calc, I charged the batteries for about 4 hours and "risked" turning it on. It worked! I checked out all the keys, wrote a simple program, and the dang thing still works. HP knows how to make a Calculator, don't they?

I will have to rebuild the battery pack... it doesn't hold a charge very long. I've gotten lots of good advice off the forum and through public and private replies, and I have the NiCd batteries in-hand.

All is not completely well, however, as the card reader definitely needs repair. The reader did pull a card through, but got an Error every time. After a couple more times through the slot, the card came out "gummy" so I know the little wheel will have to be replaced.

The latest post I read suggested using silcone rubber tubing. Is this still the preferred material? Will this rubber eventually become gummy like the original? I'm not crazy about the fuel tubing that needs the stretched-in-the-oven technique. O-rings might be easy to try, also.

Again, thanks to everyone who shares their stories and methods here. This is a great forum! I would have never considered tackling my own repair in 1000 years if I hadn't stumbled upon this forum by accident (still don't remember how I got here). My stomach used to churn everytime I thought about "losing" the 67 so many years ago, and the thought of never having it work again.


P.S.... is there a "self-test" mode on the HP-67? I seem to remember there was, and I can't seem to locate the box and manual at the moment. I've exercised all the keyboard functions, shifted and non-shifted, but I would like to give it a thorough workout if that's possible.


I have used the silicone tubing and have never had to use any "oven" technique. I have not even had to use any glue. I use pink silicone tubing that I get from a model shop and it fits perfectly.

It comes almost exactly even with the metal shoulder and its inside diameter is just small enough to fit on without any need for glue.

I have fixed many dozen 67, 97 and 41 readers using this technique.

Works for me...


Another thing to check very carefully for when you replace a gummy wheel is the state of the "clutch" in the worm gear that is connected to the motor. This clutch is a piece of nylon tube that is glued or press fit in the end of the worm gear. The motor shaft press fits into the hole in the nylon tube. In well over half the calculators that I have seen this clutch is also disintegrating causing the worm gear drive to slip. The purpose of this clutch is to provide some slip in the worm gear mechanism if a card jams.

Fixes involve either:
a) find a suitible replacement nylon tube. I have not found any stock parts of the right dimensions... if anybody has I'd love to know where.
b) make a new clutch. This requires a good mini-lathe and wire drill.
c) fold a small thin piece of tape over the motor shaft and jam the old worm gear/clutch on it. More times than not this just breaks up the remains of the old clutch and you are now in worse shape than before.
d) place a small drop of rubbery CA (superglue) in the worm gear / clutch and stick it on the motor shaft. The clutch will no longer be a clutch, but this seems to be the most reliable fix. If your drive wheel rubber is not glued down, you will still have some clutch action, but silicone rubber is soft enough that you can extract a card even if the drive rubber is glued. Be careful not to get glue into the motor bearings.



Thanks for the reply. This is exactly where I am in the process now... addressing the crumbled nylon clutch. I could never quite imagine what a "clutch" looked like or exactly where it was from the other repair articles... now I know.

The reason I found the clutch (by accident) was because my wormgear had "black gunk" in the gear teeth and I felt like I needed to clean it off. The gunk was only on one side of the gears... presumably on the bottom where the teeth lay idle for the last 13 years. So I removed the motor from its mount. While cleaning the gears, the wormgear housing literally fell off the motorshart, leaving half the nylon on the shaft and the other half inside the wormgear housing. When I tried to carefully remove the nylon from the motorshaft, it continued to crumble into pieces. There is still a little bit of nylon left inside the wormgear... I'll probably leave that there and use the gel-like superglue to bond the housing to the motorshaft, trying NOT to get any on the motor (as you pointed out).

I wondered if you could use some putty-like 2-part epoxy to stuff into the wormgear, let it setup for a minute or two, then press the motorshaft into the epoxy but remove it until the epoxy hardens. I don't know if the epoxy will shift or swell enough to give a tighter fit when reinserting the motorshaft. Or it could shrink and I'd be in worse shape.

Concerning the black "gunk"... I don't think this was from the disintegrated pinch wheel. The rubber wheel had a decidedly molasses-like color and texture, while the gunk is, well, black. I'll clean it off the wormgear and the plastic gear, but should I oil the gears a tad with something?

I've also seen several mentions of adjusting the white plastic "pin" with the slotted end. How does one adjust this without reassembling the calculator+reader, trying it out, completely disassembling the calc+reader, twisting the pin slightly, reassembling etc.?

I bought some o-rings from Lowes, and two kinds of fuel tubing from my local hobby shop. Both are made by Du-Bro and one is bright yellow, and the other is light blue. I believe the light blue is actually a silicone tubing so I will probably try that first.


Almost all epoxies shrink just a smidge when they cure.

You can try what you mentioned but getting the shaft centered and square can be a problem. Thats why I recommend finding a person with a nice small lathe or mill.

I have noticed the black stuff on almost all HP worms. It might be some kind of lube or just the worn off plastic from the roller gear.

I would recommend cleaning out all the clutch parts from the gear, otherwise the shaft might not seat fully. I have had to shim the motor back about 1/32 inch with plastic sheeting after fixing some partially disintegrated clutches with superglue. I recommend the black rubberized superglues because they are not as brittle when they dry and have less tentendcy to shear loose.


Out of curiosity, is the 'clutch' actually a clutch, or simply a flexible coupling - the main clutch action seems to be set by adjusting the friction between the card and the rubber roller.


I don't know if HP actually intended this to be a clutch or just a friction fit coupling to the motor shaft. Most people here call it a clutch. I tend to call it things best not printed in polite company...

Also in answer to how to tweak the tension on the eccentric cam pin that serves as the roller wheel shaft... I try to get it close before reassembling the whole calculator by inserting a card and feeling how tight it is when it hits the rubber wheel. You should be able to insert and remove the card without too much force. It should not be overly loose though. A little experience goes a long way here.

Once the keyboard, etc are screwed down but before replacing the back, I turn the machine over at let it rest on a battery pack and try a few cards. You can still adjust the pin tension by inserting a small flat bladed screwdriver in the slot in the cam pin's head as long as the slot is relatively vertical. If the slot is horizontal I use a right angle dental pick to get into the cam pin slot and make adjustments... it's a little tricky at first but fairly easy once you've done it once. The tension goes from minimum to maximum with about 1/2 revolution of the cam pin.


I did not realize there was an adjustment to the roller after the card reader was reasembled. I thought the nylon pin was just an axle.

I just finished rebuilding a '67 card reader, using Permatex, a silicone adhesive sealant. It seem to be replacing the "clutch" quite nicely, but the magnetic card keeps giving me an error when I push it through the reader. I now suspect it is too tight and will try to adjust it by turning the pin to loosen the adjustment.

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