[GreenKeys] New to me Model 28 and needing assistance

[John]

LK 25 usually has a synchronous pulse magnet and switch.  In other words it requires an external signal to enable the keyboard.  If it's been heavily modified, I would think that would have been disabled with the little arm located behind the magnet. 

John, W9DDD


> On Oct 7, 2021, at 2:20 PM, SK Campbell <campbellsk at comcast.net> wrote:
> 
> 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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