[GreenKeys] Model 28 KSR wall mount model

[Jim Cooper]

On 8 Sep 2024 at 18:58, David S wrote:

> tip and ring 0
> tip and sleeve 0
> ring and sleeve 0

short circuit between all sections?
that should not be ... 
are you measuring on the very low resistance scale?
 
> Are the selector magnets located near the
> "range finder" knob?  I see selector magnets
> referenced in the manual located there maybe 

yes ... they are very obvious when you see them !! 
wire wound on cores, usually two sections. 
> 
> Sleeve and chassis was the only place I got
> any resistance readings just reading on the trs
> plug part 

that's even stranger, since the sleeve is generally 
ground ... and presumably the chassis should be also. 

> I put detailed pictures and notes in - Digging
> into the Teletype Model 28 Wall Mount -
> Stickelman.net
> <http://stickelman.net/index.php/2024/09/07/dig
> ging-into-the-teletyp e-model-28-wall-mount/> -
> if there is something important I missed
> getting photos of, please let me know 

Excellent photography !

"Called a range finder in the manual, I thought this set words per minute, but 
there is a gear that does that somewhere in the machine"

speed is set by the small nylon gear on the motor shaft 
and the large gear with which it meshes.  You should see 
a part number stamped on the large gear, from which you 
can look up in a table in the manual to see what speed machine 
you have. 

The range finder is used to select what time during the data bit 
it tested to see if it is a mark or space ... ie:  for 45 baud (60wpm) 
the data bits are 22msec each ... remember Time Constant in 
an R+L circuit ...  the selector magnet has a large inductance, 
thus the current will increase from space (0 ma) to mark (60 ma) 
with a bit of delay ... let's say that delay is 2 msec ... then the 
lowest setting of the range finder that won't cause garble would 
be  2/22  (first two msec out of the 22) ... = 0.09 ...  or 9 on the 
scale of 0 to 100 on the rangefinder.  If it takes longer than 2msec
for the current to reach full 'mark current' then the setting o 
the range finder will be a larger number. 

To set the range finder (after the machine is working) we send 
RYRYRY on the local look and move the range finder to the lowest 
setting that does not garble (note the number); then move it to 
the highest number before it starts to garble (note the number). 
Subtract the smaller number from the larger number and 
divide by two --- set the range finder to that dial number. 

> Turning the motor was smooth and easy, there
> were several mechanisms that all moved about as
> I turned and no weird noises.  That part
> -seems- ok maybe, 

sounds like you are in good shape on that ...

> but the interior of the motor does not move.  

not sure what you mean by that ... if you are 
turning by hand and the main shaft is turning 
and things are happening then the motor is 
good ... remember, the OUTER part of the 
motor (but inside the metal case) is a FIXED 
winding.  The armature of the motor is inside 
the fixed winding and has the shaft coming 
out both ends -- one end for the fan, one end 
for the little gear.  

> The manuals mention a clutch that perhaps needs
> tripped? 

when you have marking loop current the printer 
should be 'idle' and not printing anything ... thus 
the clutch disengages all the character selection 
mechanism ... when the loop current goes to zero 
(space) the clutch lets the selection stuff start 
working (during the 'start pulse') and everything 
happens for the next series of pulses until the 
'stop pulse' (mark) signals the end of the character 
code.   BUT you were turning the motor with NO 
loop current, so that clutch will let all the mechanics 
function all the time. 

 > I am taking it slow and easy, ill dig into
> where the power comes in (box c) and trace out
> the tip/ring/sleeve connections - they go to
> positions 5 and 15 (and chassis) so I will
> hunt those down. 

M28 wall mount wiring diagrams are at
https://www.navy-radio.com/manuals/tty/573-116-400-iss2-6902.pdf

> 
> Thank you so much for all your help, it is
> very much appreciated