[GreenKeys] New to me Model 28 and needing assistance

[SK Campbell]

I have been a GreenKeys subscriber for some time and this is my first
attempt generating a message seeking information and guidance from the
experts. I have acquired a nice-looking Model 28 KSR from Wayne (WB4OGM).
Thank you, Wayne!
With assistance of Nick England (K4NYW) and his Navy-Radio website, we
suspect the unit had a life with the Army, which was unusual since they
mainly used Kleinschmidt's. 
It has the following components:
*	Typing unit, MX-3311/UG, LP 77 YD AGM
*	Keying unit, LK 25ARN, Stunt box AEP (WD 3047?)
*	Cabinet, LAC 203
*	Motor unit, LMU 3. The motor intermediate and pinion gears have part
numbers for 60 wpm. (I have an extra set, verified via part numbers for 107
wpm.)
*	LESU 42, WD3716 (Nick suggested that the TT-243/FG is similar, since
I could not find the WD on the Navy-Radio site for the LESU 42, I did find a
TM on eBay). Fortunately, or unfortunately, the unit appears to have been
heavily modified for other service, because the LESU equipment does not
match the original specifications. There are solid-state devices underside
of each LESU sections. (I have not tried reverse engineering the motor
control, shunt and line relays or the DC source sections of the LESU, yet.)
I have made a cautionary power up with the unit and the "Maintenance Light"
works as advertised, however, no joy with the motor or typing unit with the
"Normal On" and main power switches on. After some serious wire tracing,
resistance and voltage checks, I believe the unit could fire up. I have
tested the motor and it does run. And I cleaned the contacts on Ji/P1 and
J2/P2.

The signal path from TB 1 (back of cabinet terminals 5 and 15) route through
the signal network on the bottom of the cabinet to two RCA jacks (labeled
"keyboard" and "printer"). The motor control component on the LESU has one
lead to the same location on the bottom with its own RCA jack labeled
"motor". I believe this is the main motor control lead for the start relay,
etc. With caution, I added a 100-ohm resistor to the tip and sleeve of the
"Motor" RCA connections and the motor starts and runs without any apparent
issues. The unit appears having a satisfactory current loop (not running
open) and the red keys are operational, however, the green keys are not
responding. (The keyboard is mechanically unlocked with the red key "UNLK").
The code bar and transfer levels indicate the correct alphanumeric key when
pressed.
I have measured approximately 143vdc on numerous terminals of the main TB1
(back of cabinet), I suspect for the local loop voltage. 
Resistances to ground (RCA jacks):
"Keyboard" = open
"Printer" = 55 ohms
"Motor" = open
Voltages to ground (RCA jacks) Normal power ON:
"Keyboard" = 2.6 vdc
"Printer" = 3.3 vdc
"Motor" = 7.0 vdc

My expectation is to use an acquired HAL 5000 as a demodulator and interface
the Mod 28 and one of my vintage radios. Again, before I heavily modify this
unit back to semi-stock operation for amateur radio use, I wanted to ensure
it is mechanically sound and functionally operational.
Since I do not want to damage any components, I am seeking any and all
guidance and information on moving forward with least amount of
consternation, on possible interface connections, testing and
troubleshooting. Was this unit used with a PC and software, e.g., MTTY or
similar? I do not know.

My experience is limited; however, I have worked with a Kleinschmidt and
built a TU for it back in the 70's and always wanted to get back into RTTY.
During my telecommunications career, I was assigned to the toll test board
department and TOC (I really enjoyed that work), where we used Model 28s for
monitoring and testing of local loops for the USAF, NWS, and law
enforcement; any TTY mechanical issues went to the local private-line
repairman. Recently, I have watched numerous RTTY YouTube videos (Marc and
Ethan) and have gained a greater understanding and extremely thankful that
GreenKeys is so active and a positive resource!

Thank you all, in advance.

Steve W7SKC
W7SKC1 at gmail.com <mailto:W7SKC1 at gmail.com> 
campbellsk at comcast.net <mailto:campbellsk at comcast.net> 

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