[GreenKeys] loop supply - part 2

[John, W9DDD]

Good Morning Virgil

Wondering how badly the LESU is messed.

Perhaps it would be useful to describe how a unit would come from the 
factory.

First both magnets are for the typing unit (the LP).

They may be wired in series or parallel.  (for 20 or 60 mA) (What is the 
value of those two power resistors wired in parallel?)

Normally the wires go to the 20 pin connector on the printer and then 
out the mating connector to the A terminal on the bottom of the LESU.

The selection of 20 or 60 mA connections are made on the A strip which 
unfortunately required inverting the LESU.  (why aren't the choices 30 
or 60?)

Then depending on whether there is a polar relay in the LESU, the 
selector magnet leads either go straight from the A strip to the C 
strip, (the one on the back wall of the cabinet) or through the polar 
relay assy and back to the A strip and out to the C.

If you wanted to describe or send pictures of the LESU I could refer you 
to WD that was close.


Those of use who mess with these things frequently have made up a set of 
test cables which bypass all the extra stuff.

I inherited one KSR which had Bell System inside wire hooked directly to 
the keyboard contacts and a connector and shielded cable going to the 
LP.  For some reason I assumed the connector was internally strapped for 
60 mA.  I ended up with a high resistance coil on one of the two 
selector magnets.  I'm not sure if I got it that way or I damaged the 
coil because it ran it a fair amount that way until I started to restore 
the original wiring and realized I had a problem.


I seem to recall you're down around Austin/San Anton area, kind of 
stretch for an in person consult, I'm on North side of DFW.


On 5/19/2023 7:31 AM, Virgil Bierschwale wrote:
> Thanks to you folks, I now understand how the loop supply is wired in.
>
> The model 28 KSR I have has a LESU with no part number, and broken 
> wires, things like that.
>
> So I want to wire the loop supply directly to the selector magnets 
> (unless there is a better way).
>
> There are two selector magnets, so there are 4 wires.
>
> They appear to be orange, yellow, brown, and white.
>
> Any advice on how I should hook up the loop supply here?
>
> It's been a long time, but I'm assuming one selector magnet is for the 
> typing unit, and the other is for the keyboard.
>
> My long time goal is to hook this up to an arduino so that I can send 
> reports to it periodically.
>
> Thanks,
>
> Virgil
> N5IVV
>
>
>
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-- 
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The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD

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