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HP Forum Archive 02

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HP46 printing problems
Message #1 Posted by Reinhard Hawel on 11 Apr 2000, 7:44 p.m.

My new HP-46 sometimes prints, sometimes not. I know the swotch at the top row to forbid printing and I always have printing set to "on".

Sometimes, when I print the printer does no line feed and always prints to the same place. Sometimes it doesn't even stop printing (and makes a hole into the paper rather fast), but prints continously with no line feed onto the same position. When I'm hitting the "print" button 2 or 3 times, it stops printing and behaves like it should (sometimes).

Does anyone have a clue ?

Ah yes, the rest of the calculator works great.

Re: HP46 printing problems
Message #2 Posted by Andrés C. Rodríguez on 13 Apr 2000, 9:33 a.m.,
in response to message #1 by Reinhard Hawel


I never had an HP 46, so take this just as an idea to be checked:

I designed data capture equipment in the eighties, so I had to work with small printers (similar to those found in calculators and cash registers). Specifically I used dot-matrix, impact printers.

In most models there was no room for a line-feed motor or solenoid. The trick for paper advancement was to move the printing head some columns from its rest position; when the head returns to the zero column, it strikes a lever that feeds the paper. (The head "hammers" into the lever). I think the HP41 printer works in thsi manner, too.

In some models, there was a variation: the head strikes the lever, engaging a gear/clutch for a while. While the gear (or clutch) was engaged, the motor that normally moves the head in the horizontal direction gets coupled with the paper feed mechanism. After advancing one line, the same gear/clutch gets uncoupled. The uncoupling was achieved because of the particular form of such gear/clutch, with a small tooth that locks or unlocks during each revolution of the gear.

I realize that putting this in text, many years later, and using my English, is rather inappropriate. Perhaps if you find some catalog for small impact printers from Epson, Citizen, Brother, etc. you may have a better description, figures, etc. of the general idea.

The lesson I learned "the hard way" on that project was about mechanical wear. Those printers were specified for about 2 million line-feed operations. It seemed like a lot, but when you print a good number of tickets each day, and use this mechanism not only for printing but also for paper advance, the life of such mechanism may be less than a couple of months (!!).

IF (and this is a big "if") the mechanism on your HP46 is somehow similar to those I worked with, you may try to find a small metal, curved piece ( C shaped ), about 1.5 cm long, that is struck or moved when the head returns to the zero column. Since your printer sometimes work, the piece should show some wear, but you use it as a template to find a spare. Or you may find some mechanics technician that could make some new pieces for you. (I think that electro-erosion may be appropriate)

Again, this is just an idea; I hope it may help

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