Monroe electromechanical calculators

Jules Richardson julesrichardsonuk at
Thu Jun 16 07:42:56 CDT 2005

I brought one of these home from Bletchley last weekend - turns out
they're quite addictive little things :-)  It's a Monromatic 8N-3-213
which was marked as broken - I thought I'd see if there was anything
obviously wrong inside, plus of course I was curious as to what the
innards of such a machine looked like.

Question - does anyone have service information for these machines
(yeah, right!) or useful tips on things to check over?

So far I've found an acorn jamming up the works (!!) and lots of dirt,
but the mechanism's reasonably oily still and in good condition. Some of
the keys seem to jam occasionally or not latch - I'm hoping that's down
to dirt rather than wear (it seems to be improving the more I tap away
at things to be honest).

After checking that everything was free to turn without jamming I
applied power...

There's some earth leakage which would be useful to track down -
possibly a break-down in cable insulation? I've not worked out what the
large rotating thingy on the outside end of the motor shaft does yet
though, as this seems to be connected to an insulated plate (and throws
off quite a few sparks when running)

Can't say I've ever seen such a complicated thing. Electronic circuits
don't even come close in complexity :-) I don't think I'd be up for a
complete stripdown and rebuild; I'd never get it all back together.

ps. Is there a better place to ask than here? Not sure whether
electromechanical calculators are on topic or not!

pps. Anyone care to guess a date for this machine? I'd make a wild guess
at mid-50's but really don't know.



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