HP-91, HP-97 Printer Service - common issues


Hi all,

For you collectors of the HP-91 or 97, I would like to correspond with people who have refurbished the printer - probably off-board. What common problems have you seen and how can they be fixed? What thermal paper is available now that works well?

I have one 97 with the spur gear problem and read Katie Wasserman's article on that. What other problems are common?


-- Dan


I've had the following problems with my various 97 printers:

- a broken plastic gear wheel, for which a metal replacement part was suggested on this forum. Good fix!

- the white rubber wheels on the transport mechanism, which become flat if the printer is not used for a long time. If they do, the printer feed mechanism occasionally advances paper less than an entire line. I think this the most common problem, and I have not found a fix for this issue

- a broken printer head flex cable - one fellow in this forum successfully soldered it, but my attempt to do so failed. I will give it another try one day

- uneven printing. On one printer, cleaning the head arranged things, on another one, the problem remains.

- too light printing. There is one article on the forum explaining how to adjust print density by replacing a resistor, but I found that the most likely cause is just old thermal paper.

Anything I forgot?


Edited: 9 June 2007, 7:52 a.m.


Good list! I'll just add one problem:

The tiny plastic rails that hold the clear plastic print window in place are sometimes broken and that the print window is often missing when you find an old calculator (potentially because of the broken rails).



So we made the list of known problems - but what about the fixes?


There are some recommended fixes in this list. What we're missing is a detailed take-down guide like we have for the gummy wheel.

As I fix mine I'll log some notes and take pictures. Perhaps later I'll submit such a guide to the Museum library.

-- Dan


For the iddler gear, I've put a few pictures and a procedure on my site.

When the quality of the procedure will be acceptable enough, I'll try to put it as an article on the Museum.





The reed switch that commands the print head moves sometimes fails or breaks.

It can be replaced but final adjustment is quite difficult.




Thanks for your comments! I have two 97's with printers to repair. One makes a whining noise whenever I turn on the calculator. One has the broken spur gear. I've ordered the spur gear replacement from PIC Designs per Katie's article. But they're rather slow on shipping - that was 2 weeks ago.

Does anyone know where to get replacement thermal paper? Especially with blue printing?


-- Dan


Blue printing paper might be hard to find, but black printing paper is easy. I use NCR's 2 1/4" x 85', you can buy this on ebay for next to nothing:


Edited: 10 June 2007, 1:43 a.m.

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