Friden EC-130 calculator schematics?

Rick Bensene rickb at
Sat Oct 15 09:58:08 CDT 2005

> Brian Knittel wrote:
> This is a bit off-topic, since the device isn't programmable, but... 
> does anyone have a set of schematics and/or a service 
> manual for the Friden EC-130 electronic calulator?  Google isn't coming up
> with anything but others' requests for the same.

I've been looking for schematics for this machine since the early 1990's,
as yet have come up dry.  They just don't seem to be out there.  My
is that generally, service technicians in the field were trained to repair
the machines
on a module basis, e.g., replace this circuit board if it exhibits this
Service technicians didn't need schematics, because all they really needed
troubleshooting guide, a knowledge of general operating theory, good test
and a kit full of every spare assembly needed.  This made it unnecessary for
them to repair things down to the component level, except in the case of the
supply, which may require replacement of individual components.  Everything
else was modular.  As a result, field techs likely didn't need schematics --
that was a good thing, because field techs could be 'loose' in their care
of schematics, allowing copies to be made, leaving them behind, etc., which
generally not maliciously intended, could result in competitors getting
their hands
on the design, which, in those days as it is today, can be a big problem.

The closest thing out there are the US Patents that describe the machine.
The patents are quite detailed, and diagram everything at a 'building block'
level.  They are likely not a 100% accurate reflection of the actual
EC-130 (for a number of reasons), but they give a great level of detail
the architecture and methods by which the machine operates, and lots of
level "schematics", and timing diagrams.  The relevant patent numbers are:
3465301, 3523282 and 3546676.

You can get to these patents online through the US Patent & Trademark Office

Nicholas Bodley (a former Friden service technician) wrote an essay on his
of the architecture and operation of the machine.  You can find this on my
website at  Reading this, combined
absorbing the data in the patents, can give someone with a solid electronics
background a good idea of what is going on inside the machine.  Making an
extender board, and with good test instrumentation (a good four-channel
is invaluable, and if one is available, a logic analyser with settable logic
thresholds), it should be possible to track down where the problem lies.

The most common problems with these machines are failures in the switched
capacitor voltage multiplier that generates the 3KV for the CRT, problems
with the delay line adjustments or component failuers in the delay line
transmit and/or receive amplifiers, and lastly problems in the CRT
circuitry.   Failures in the logic package are pretty rare, actually.

If you can describle the problem(s) you are seeing with the machine, I might
be able to provide some hints.

Rick Bensene
The Old Calculator Web Museum
Beavercreek, Oregon

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