HP-97 printer repaired

[PANAMATIK]

My old HP-97 calculator had the well known issue not to transport the paper any more due to the slippery rubber wheel, which did not have enough grip. The repair instruction found in the forum told me, that I had to mechanically disassemble the printer completely to get access to the wheels. Sigh! Normally I have better skills in repairing the electronics. But when I started the disassembly I found it was not too difficult. I wanted to avoid to remove the rubber wheels, because I think they are really difficult to replace. So I decided to add some grip by surrounding them with heat shrink tube. This was not my idea, I have seen it somewhere, but I don't remember where. Anyway many thanks to this brilliant idea.



It was some work to assemble anything and to try, whether it worked. My first attempt failed, because the 0.5 mm additional wheel diameter with the tube caused the printhead to stick at the far right home position. There was not enough space between printhead and the wheel. I had to open the calculator and remove the printer again. But there was an easy solution. I released the screw of the magnetic home switch and moved it 2 mm to the left and now it does not interfere with the printhead mechanic. And after testing it works perfectly, hopefully for a long time and many paper rolls.

The keyboard and LED display of the HP-97 is superior to any other LED calculator I know. So I'm very happy to have this calculator fully working, also the card reader was repaired some time ago.

Thanks to all of you for your ingenious mechanical and other repair solutions.

Bernhard

[PANAMATIK]

Today I tried to repair the printer of another HP-97 with heat shrink tube. The paper transport was definitely not working.

I disassembled the printer, trained by the last time success, and tried to fix the heat shrink tube on the two paper feed rolls. This time the task became more difficult, because the tube slided away from the center of the rolls while shrinking and I recognized that I needed a smaller tube diameter, which I didn't had at hand. While heating I observed a small oily film emerging from the original rolls, like fluid rubber. After cooling down I removed the oily substance and recognized that now the surface seemed to have much more grip than before. So I decided to reassemble the printer without attaching the heat shrink tube. And to my surprise it works flawlessly.

I don't know whether this is a permanent repair, or even whether HP intentionally provided a material, which allows to refurbish the paper feed rolls, just by heating them up and let cooling down. I have a third HP-97 printer repair in schedule for next time, perhaps I will try the same again.



This is the result: perfectly aligned print lines.

Bernhard

[PANAMATIK]

(06-18-2017 12:26 PM)PANAMATIK Wrote:  ... I have a third HP-97 printer repair in schedule for next time, perhaps I will try the same again.

I couldn't wait to open and repair my third HP-97 with defective paper feed, just by heating up the two paper feed rolls for a few seconds with a hair dryer. I disassembled the printer mechanics before to avoid heating up other parts. Was done in half an hour including assembly. And it works too.

Now it needs a long time observation and extensive testing when my next income tax must be calculated. Not before next year

Bernhard