[GreenKeys] M28 - mystery LESU

[Nick England]

 Seeing the cloth-covered wires made me think it was an early model. I have
a TT-47A with a LESU that looks very similar except no loop supply which
looks like a ham add-on.
The TT-47A LESU is Navy model SB-154A. Teletype model LESU5/103
Manual is at
https://www.navy-radio.com/manuals/tty/tt47a-91713-5207.pdf

Wiring diagrams 2852WD and 2853WD are in 573-100-400
https://www.navy-radio.com/manuals/tty/573-100-400.pdf

Nick England K4NYW
www.navy-radio.com


On Mon, Jul 14, 2025 at 1:59 PM Duncan Brown <duncanancy at earthlink.net>
wrote:

> I'm checking out a M28KSR that looks like it has had some major rewiring
> done to it.
>
> All the jumpers that are normally on terminals 4-14 of the cabinet
> terminal blocks have been removed.  There were two, 4 conductor, external
> cables connected to the cabinet terminal block, all unterminated, except
> for a 2k power resistor (loop current limiter) connected across  C10-C11.
>
> I see no designator on the LESU and the color codes of the cable from the
> LESU to to c5 - c14 do not match the colors I see on 2874WD (or any
> others).  The LESU has what looks like a Line Shunt Relay, a 120VDC power
> supply (with monitor jack), a Motor-Stop relay and an 120VAC input panel (
> lamp switch & fuses). See picture enclosed.
>
> Can anyone identify this LESU?
>
> I tried to remove the LESU by removing the big screws.  The LESU was
> loose, but would not come out, apparently because of the front panel power
> switch extension mechanism.  I expected it to disengage when I lifted up
> the LESU, but it did not.  Is there something in the switch extension
> mechanism that has to be removed/released?
>
>
> Thanks,
>
> Duncan
> K2OEQ
>
>
>
>
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