[GreenKeys] Model 28 KSR wall mount model

[Jim Cooper]

On 4 Sep 2024 at 18:52, David S wrote:

> Photos are attached
> 
> TT6.jpg is the 1/4in audio jack, same kind of thing I see electric
> guitars use.  Been forever since I have seen one.

Notice first that the plug (not jack) is a TRS type ... 
Tip - ring - sleeve 
My guess would be that is the way the unit is connected 
into the "local loop" -- which is generally a 120vDC source
with a big (power) limiting resistor which sets the "loop 
current" to either 60mA or 20mA ...  depending on how 
the selector magnet is wired. 



Often such a plug is wired using the tip and ring so that 
the sleeve (and the sleeve of the jack into which it plugs) 
is not hot with the 120vDC ... 

I would strongly suggest that the first thing you do is 
to use an ohmmeter and check if any of the three wires 
on the plug go to terminals on the selector magnet.  
Actually, before that measure the resistance between 
tip and ring 
tip and sleeve
ring and sleeve 

this can give you a clue what is on the other end of the wire! 

if you DO get continuity between the plug wire(s) and the 
selector magnet, that will immediately confirm it is the 
loop plug.  If no continuity, then you'll have to physically 
trace the plug's wire into the guts and see where it goes; 
it may well go to the Electrical Service Unit -- which will 
lead you to a fascinating expedition of discovery ... 

> TT5.jpg is the bottom shelf area of
> this wall mount unit, which houses
> the paper spool and the "Electric
> Service Unit".  The 1.4in audio jack
> cable comes in on the right side as
> a grey cable, extends to the far left
> and enters behind the lower black
> cover panel. 

OK, then the gray cable does NOT go 
into the metal box "C" I presume.  It looks to me like it 
goes in behind the black cover of the terminal strip; so 
you will want to remove the black cover and determine 
what terminals the gray cable goes to....   if you can find 
ANY indication of a military or Bell System configuration 
ID you might ask on Green Keys if anyone has the schematic 
for that configuration. 



The plug at "D" looks to me like an AC plug. 
You will want to take the cover off box "C" 
and see what is inside ... might be a heavy duty 
"motor control" relay, OR something else. 

You will spend a lot of project time playing 
detective, trying to find out what is connected 
to what ...  hopefully you are good at drawing 
schematics and/or wiring diagrams !!

> There is disintegrating material on
> the interior walls which I assume
> could be sound dampening foam of
> some sort?  It crumbles to the
> touch.  

Yes, that WAS sound dampening foam! 
and it is very common for it to disintegrate 
over the years. 

> The important stuff like wires and
> metal all appear in good shape, just
> dirty. 

Before you apply any power to the unit, 
and after you do your basic cleanup, you will 
want to manually turn the fan on the motor
(be careful at first that you are turning in 
the direction that causes the gears and 
mainshaft to turn; if not, stop and turn the 
other way).  You want to be able to manually 
turn the motor long enough to be sure that 
the main shaft and all the other 'stuff' is 
working freely -- no sticking or binding. 
 
> I may have been lucky in finding
> this wall mount unit, it appears to
> be uncommon, and coincidentally
> perfect for the application I have
> in mind. 

wall mounts ARE quite rare... 
your situation is called SERENDIPITY !!

> > btw, I have a mint (in original sealed foil packaging)
> > copy of TM 11-5820-402-10  Technical Manual
> > for AN/VRC-12, -44, -46, -48, -49 ...  rather than try
> > to pedal it on eBay for whatever, I'll slip it into the
> > box with the M28 manuals.
> 
> Yes please, thank you so much,  I will put it to good use.

There was no space left in the M28 manual box to put 
the TM 11 in, so it was in with the two rolls of paper. 
The M28 box is full and is already sealed and addressed, 
so I'd rather not take it all apart now.  
> 
> >> Are you signed up on the Green Keys chat group?
> 
> I did find that and am reading a
> bunch.  I have alot of terminology to
> learn and concepts to grasp.  This
> machine is fascinating, I really love
> these electromechanical devices. 

Everyone on that list loves the electro-
mechanics, as well as the sound and smell
of these machines !    The list is a great 
resource to learn from, and a great bunch 
of guys to ask for help and info. 

> The more I read the more I am sure I
> will have to get a terminal device,
> its good there are some options.  I
> had the (incorrect) assumption I
> could connect via any serial RS232
> and have that work. 

Keep in mind that all Teletype machines, 
excluding the "newer" ones that were for 
crypto and use extensive electronics inside, 
were built to run on DC current -- turned on 
and off in 'binary code'...   Baudot code for 
all up to Model 28. 

To interface the DC current loop (60mA or 20mA)
with RS-232 you would need a suitable converter. 


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