Introduction + OT TI question


Hi everyone,

This is my first posting to the group.

I have a small collection of calculators - various HP, TI and Commodore machines - from the 1970s. They are all scientific, and some are programmable. Since I am old enough to remember when they were new, I mostly collect them out of nostalgia. None of today's gadgets have the WOW factor that these machines had back then.

First of all, I apologise for my first posting being off-topic. I have not found any other forum on this subject with any activity, so I thought I'd post it here and hope for the best.

My latest acquisition is a TI SR-52. When I first got it, a couple of days ago, It came with a lot of cards, and I was amazed to find that the card reader worked. Now, the card reader is leaving a sticky black residue on the cards, and will not read them any more. I opened up the calculator and found what I assume is the "gummy wheel" problem that I have read about. The rubbery wheel is soft and sticky. I washed off the contaminated card as detailed in the manual, but I assume it's probably had it. I think the calculator hadn't been used for a long time, and so the wheel worked a few times, and then disintegrated. Is this very difficult to fix?

When I put the calculator back together, it behaved as if it had no battery in it. When connected to the ac adapter it flashed and whirred, which can burn it out. Without the ac adapter it didn't work at all. I later found that a gentle thump to the left hand side of the calculator got it going again, so as of now it's working OK. Obviously something is loose. Does anyone have any idea what it is?

Finally, I also discovered that the calculator works perfectly when connected to an off-the-shelf variable ac/dc adapter set to about 3.5 volts. Is this safe, or is this another way to destroy the calculator?

Thanks to all for your patience,



Daniel --

Welcome, and no need to apologize (US English).

Regarding the "gummy wheel" problem, all I know is what I have read. I've had a 1982 HP card reader rebuilt by eBay seeler "plasmoid".

The basic problem is that the polyurethane(?) compounds used in the 1970's and 1980's for these purposes were unstable -- they crumbled and eventually disintegrated into goo. Modern compunds are stable.

A solution might be to find modern tubing of suitable inner and outer diameters that would provide a suitable replacement for the old rollers. Be sure to clean off the residue, or course.

I can't speak about SR-52 internals, but I personally destroyed my 1977 TI-30 in 1981 by connecting it to a dc power supply at 9.0 V after yet another battery died. It was designed for 9V, but I may have reverse-connected the power supply leads.

-- KS

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