[GreenKeys] TD wiring in 28ASR notes

[Nick England]

Just for the archives - here are notes from a recent conversation about TD
wiring in a 28ASR - maybe they will be helpful to someone else some day. I
am the proverbial dangerous person with a little knowledge so
corrections/clarifications are welcome.
Nick

There are two independent circuits for the TD -
1) clutch magnets (run-stop)
2) signal generator

1) The clutch magnets on the TD are usually hooked up to 115vac through the
TD control switch, TD tape out switch, keyboard lockbar switch, and K-KT-T
switch. You can see that in the W0700 diagram at lower left of the first
sheet.
http://www.navy-radio.com/manuals/tty/28ASR_wiring_W0700.pdf
In case you haven't run across it before, in these schematics an X across a
line means "normally-open contact" and a | across a line means "normally
closed contact".

H is the connector where the TD plugs into its base and U is the connector
on the ASR base where the TD connects to the terminal strips C.
H4/H5 go to U8/U11 to C134/C140. Make sure there is a jumper C135-C136 and
also C137-C138-C139 (these are intermediate connections  for the TD control
switch and the TD tape out switch which run from the TD to the C terminals
and back to the TD because that's how Teletype did things - see details on
W0700)

Then make sure you have 115vac at C134/C140 in order to energize the TD
clutch magnets

Of course there are other ways it might be wired  up - including running it
off the LESU DC loop supply as shown in
http://www.navy-radio.com/manuals/tty/wd-tty-7015-7016.pdf
- but even then, H4/H5 to U8/U11 to C134/C140 is still the energizing path.

2) The TD signal generator contacts are in line with the keyboard signal
generator. Connections are shown at the top center of the first sheet of
W0700. H19/H20 go to U0/U2 to C129/C130. So you need to check that
C129/C130 are in series with the keyboard signal generator when in T and KT
modes. Since the TD signal generator is in line with the keyboard, pulling
out the TD will indeed open the line and cause the typing unit to run open.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20150725/5204c611/attachment.html>