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Looking for Silent 700 printhead

DrCharles

Experienced Member
Joined
Sep 2, 2014
Messages
101
Location
West Plains, MO
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
 

DrCharles

Experienced Member
Joined
Sep 2, 2014
Messages
101
Location
West Plains, MO
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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