Just bought a HP-67 calculator at an auction

[[kby]]

(07-30-2020 01:13 AM)teenix Wrote:  

(07-29-2020 11:20 AM)Harald Wrote:  Well, if the card read has NEVER been used, maybe there is a chance it still works. I suspect the deterioration of the wheel is triggered by contamination. Maybe it gets contaminated by the cards, but maybe just air getting in is enough. Would be interesting to find out...

Hard to say. HP says it had to use a "special" polyurethane compound to provide reliability over many operating factors, so it may degrade at different rates to other polyurethane types. I don't know much about chemistry but it appears these can degrade due to many factors including temperature, location (sea-side etc) and residue or hungry little microbes which might get transferred from your fingers to the cards to the wheel.

Maybe if the calculator survived packed in its box in a cool and dry environment over the years, the wheel might still be ok.

cheers

Tony

From the generally available literature at the time, HP's principle criteria for the HP-65 pinch rollers was the "grippiness" of it even under adverse conditions (oily cards and low temperatures are the examples they talk about). As such, while I'm sure they wanted it to last the expected "life of the calculator", longevity probably wasn't as important, and something that might have been too hard to optimize on top of the other two criteria, especially with 1970s era polymer chemistry. It's still a bit of a black art, but things we can can control much better now than then.
I don't know what TI used for their rollers as I've never owned let alone disassembled a TI calculator.
Regular rubber pinch rollers are susceptible to oxidative damage primarily by ozone, so that would mean it depends on how polluted your local air is. The other major killer is often UV light, but that should not be an issue for the pinch roller.

Oddly I have one -65 (which is assembled from the best parts I had from several), but the machine the reader came from appeared to have never had the roller replaced. It wasn't one of the usual things (tubing, washers, etc.). I also recall the label on the back of t he machine the reader came from (can't remember if it was actually a -67 or a -65) did not appear to have ever been removed (I know that can be hard to tell if it's really done well, but usually there are some tell-tale signs if you know what to look for). Additionally, this roller is black; the original ones are a pale translucent yellow.

Interestingly enough some person on TAS sells pinch rollers for TEAC open-reel tape decks made of the urethane because they are softer and do grip better; the original ones get glazed and hard sooner than one likes. However, although i initially thought this seemed like a good idea, I quickly remembered that the HP-65 pinch rollers were also polyurethane, and, recalling all of my experiences with the gummy wheel, decided they were a really bad idea for quarter-inch quarter-track magnetic tape. Cleaning the goo off of the cards without damaging the card is much easier than it would be for flimsy tape.