[GreenKeys] Model 28 KSR wall mount model

Mon Sep 9 11:09:10 EDT 2024

I haven't ever seen a wallmount unit in person so this is very interesting
to me.
More photos would be great! Particularly of ID tags and the LESU.
FWIW, miscellaneous observations -

A standard wall-mount configuration I found included a printer with the
following
LK74ARK/BR keyboard/base (ARK is the typebox config, BR is the color)
LPC 215BR cover/backplate
LESU72 electrical service unit

The LESU72 includes a selector magnet driver (SMD) which I can't tell from
the photos whether you have.
Anyways, the LESU actual wiring diagram is 4486WD (4 pages) and the
schematic is 4487WD (one page) included here
https://www.navy-radio.com/manuals/tty/573-133-400-6911.pdf

The 4487WD schematic covers the complete machine
(printer/keyboard/base/LESU) so is probably really useful.
Of course if yours has been hacked it won't be totally correct, but it will
provide a lot of useful info.
I do see that it has a line shunt relay, so that would short C5-C15 when
the power is not on.

The LK74 actual wiring diagram is 4484WD included in
https://www.navy-radio.com/manuals/tty/573-116-400-iss2-6902.pdf

>From the photo it appears the red KBD LK key is depressed which (no
surprise!) locks the keyboard.
The M28 keyboard doesn't reset except mechanically at the end of a cycle,
so even if it is UNLK, you wouldn't get more than one key push unless the
motor is turning to complete the cycle.
This machine may have auto-lock, meaning if it runs with the loop open for
two characters, the keyboard automatically locks.
(that was a way for another machine in your loop to keep you from typing so
that they could send a message)
This feature is not normally a nuisance except when testing and you need to
keep hitting the red UNLK key.
But it isn't hard to defeat - something to do later.

The LESU parts document is here
https://www.navy-radio.com/manuals/tty/jh/ttyman7/TeletypeManuals/model28/573-133-804TC.pdf

The cover/backplate parts doc is here
https://www.navy-radio.com/manuals/tty/jh/ttyman7/TeletypeManuals/model28/573-134-804TC-Iss2.pdf

I see from your photo that the typing unit is Teletype model LP102 (Bell
28AH).
Is there an ID tag on the keyboard base?
Anyway the wiring diagram for the LP102 typing unit is 4355WD in
https://www.navy-radio.com/manuals/tty/573-115-400-6812.pdf
which is pretty conventional with selector magnets on pins 0/3 and 1/4 of
the connector.
(you may need to trace those wires if the unit has been modified.

BTW, the standard Teletype sprocket drive paper is 8.5" hole-to-hole, not
9" (8.5" print area) like almost all computer paper.
You can find a paper source in the greenkeys archives somewhere.

The installation spec is here with perhaps some useful info
https://www.navy-radio.com/manuals/tty/jc/50170s-ISS2-6306.pdf
I think this is the same info
https://www.navy-radio.com/manuals/tty/573-100-201-6404.pdf

Have Fun!
Nick England K4NYW
www.navy-radio.com

On Mon, Sep 9, 2024 at 7:41 AM Nick England <navy.radio at gmail.com> wrote:

> 1. Some Western Union machines did tie one side of the signal line to
> chassis. Bad idea in my mind!
> 2. The LESU may have a relay that’ll short the signal lines if no AC power
> applied.
>
> I’ll look at your photos.
>
> Nick England K4NYW
> www.navy-radio.com
>
>
> On Sun, Sep 8, 2024 at 10:41 PM Jim Cooper <w2jc at optonline.net> wrote:
>
>> 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
>>
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