[GreenKeys] M28 - mystery LESU

[Duncan Brown]

John,

That looks like the right schematic!

Nick had identified it as an early Navy unit, TT-47 (actually a TT-69, 
since it is a table model) and sent me to the manual, NAVSHIPS 91713, 
which shows the LESU wiring color codes (fig 3-3) that matches this unit.

Nick - you questioned the DC supply ("rectifier") in this LESU. In 
NAVSHIPS 91713, p 1-12, there is a note about an optional rectifier an 
it shows up in fig 3-1.

The military nomenclature plate had been removed, or I would have known 
where to look for documentation.  I can see a spot on the cabinet under 
the keyboard, where a label has been removed. there is also a red 
inspection? stamp that looks military?   See pic.

Thanks!!!

Duncan
K2OEQ






On 7/14/2025 4:36 PM, John, W9DDD wrote:
> I see you have the 3 terminal strip version, this might be closer?
>
> From from page 3 of
>
> https://navy-radio.com/manuals/tty/573-133-400-6404.pdf (wonder where 
> page 2 went?)
>
> The long rod for the power switch has a groove in the end of it that 
> keeps it in a hole in the LESU frame.   The rod also runs through a 
> spring attached to the cradle.  I usually try to wiggle the rod back 
> and forth to get it out of the hole and leave the spring in place.
>
> My approach would be to check wire colors on the bottom side of the 
> terminal strips to see if they are per the schematic.  A general 
> thought is that the jumpers on the top side configure the 
> interconnections of the parts in the LESU.  (take that withe a grain 
> of salt).
>
> On 7/13/2025 6:16 PM, Duncan Brown 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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>
> -- 
> ---
> ----
> The above comments or recommendations are SWAG. Use at your own risk.
>
> John, W9DDD
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