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Thread: Looking for Silent 700 printhead

  1. #1

    Question Looking for Silent 700 printhead

    I have two Silent 700 terminals (model 745) that I bought quite a few years
    ago (nonworking). Couldn't find a schematic. Last week I just happened to
    search for one - and found a complete service manual with theory of
    operation and full schematics! So I got them on the workbench.

    The more worn one wouldn't print anything on the paper but was otherwise
    working. I found that the nylon printhead pressure adjustment wheel had
    split and fallen off the solenoid shaft into the case, along with the
    pressure spring. Then it would print, but I promptly discovered that the
    printhead has several "dots" missing in a pattern that could not be
    accounted for by the driver circuitry. I confirmed it by swapping the
    printhead from the other one, and now it prints perfectly. So at least I
    have one working now

    The second one in half-duplex mode will only beep (Ctrl-G), CR and LF in
    half-duplex mode, so I know the keyboard is alive and there is power.
    But it otherwise won't move the carriage forwards (including space), or
    print any characters at all.

    Before I go to the trouble of diagnosis and repair, does anyone have a good
    printhead, or know where I can find one?
    No point in fixing it if the characters won't be printing properly when I'm
    done...

    thanks
    Charles

  2. #2

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    The other terminal had the nylon thumbwheel (on the printhead pressure adjustment) split and fall off. So I fixed that by drilling the knob and the shaft and pinning them together. Installed the defective printhead and the terminal does receive and print now.

    Then I found out that four of the keys don't work any more. Hall effect key switches are no longer obtainable... and manually jumpering the contacts prints the correct character.

    So now I need either a working keyboard, or a non-functioning one that I can disassemble (which is somewhat destructive due to the mechanical design) and salvage four key switches. And a printhead

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