[GreenKeys] WU 28ASR Wiring

[Don Robert House]

THANKS MUCH JACK!

I hope to get this nice machine up and running.

Happy holidays and travel safely please.

Don


On 16 Dec 2006, at 3:04 PM, Jack wrote:

ZCZC

For Fred, N9FT and Don, K9TTY, and others:

The following can be used to rewire Western Union
Teletype Model 28ASR's; this is the most
"non invasive" approach to getting the machine
going.

This information assumes the internal (GREEN)
"9797 Wiring Cabinet" is intact and unmodified and
the polar relay is in place and properly adjusted. The
changes allow the machine to be used "on line" with the
internal polar relay and loop. The polar relay's line
coil is operated by your loop (RTTY converter, local
loop, etc.). The relay in turn operates the printer
through the internal loop. The keyboard and tape reader (TD) are
in series with the internal loop; or, the keyboard and
TD can be wired externally to be in series with the
external loop (allowing it to key your AFSK, etc.).

These changes are based upon a Western Union schematic
dated 1966 (originally drawn 1959). All of the changes are
done at the rear "C" strip on the back inside of the
28ASR cabinet. You do not have to lift out the
wiring cabinet. The following assumes the TD has
power to the control solenoid through the existing
wiring and it runs when you put a tape in it.

Here goes:

REMOVE THESE JUMPERS:

132-4, 131-10/11 (leave 10/11 jumpered), 132-136,
32-139, 13-15, 7-12, 5-8/9 (leave 8/9 jumpered), 125-31

ADD THESE JUMPERS:

4-132, 15-131, 6-13, 125-150

The polar relay line coilconnections are
at (actually there are two "line"
coils used in parallel with this type of relay) :

8/9 and 10/11 (these connections are jumpered) one
lead goes to 8/9 and the other goes to 10/11. These
two leads then go to your external loop/TU.

An external SPDT switch wired between 13 and 142 would
put the TTY into a "local test" mode, allowing you to use it
without the external loop. This shorts out the polar relay's
contacts.

If you want to bring the keyboard and TD connection out of
the internal loop, you can get the KBD and TD here:

KBD -   4-6
TD -  131-132

There should not be any jumpers on these terminals. You
could wire a jumper between 131 and 132 and then get the
KBD and TD in series at 4 and 132. To test, look for a short
with an ohmmeter and operate the TD and KBD to see the
short changes with typing or tape. You would have to put a jumper
between 15 and 13 for the printer to remain in series with the
polar relay and internal loop.

Fianlly-

Check for relay bias at the "BJ" jack and adjust it for
half of whatever you external loop is (e.g., if you have
an external 60 ma. loop, adjust the relay's bias for
30 ma. with the "BP" potentiometer).

Check the printer's selector magnet current at the
"PJ" jack; it should be 60 ma., adjustable with the
"PP" potentiometer.

CAUTION - THESE CONNECTIONS ARE BASED UPON THE SCHEMATIC I HAVE.
IF YOUR MACHINE IS DIFFERENT THAN THE 9797 WIRING CABINET'S
CONNECTIONS, YOU'RE ON YOUR OWN.

I TAKE NO RESPONSIBILITY FOR ANY DAMAGE TO YOU OR YOUR TTY IF
YOU MACHINE ISN'T IN "STOCK" CONDITION WITH A 9797 CABINET.

If you want to make things simple, bring out the KBD and
TD contacts as described and then wire the printer magnets
in parallel right at the magnets and bring them
out, too. Unfasten the plug that
goes to the printer and tuck it out of the way.
This eliminates all internal signal
wiring, the polar relay and the loop. Wire the
KBD, TD and printer in series.

73,
Jack WA2HWJ

NNNN



_______________________________________________
GreenKeys mailing list
GreenKeys at mailman.qth.net
http://mailman.qth.net/mailman/listinfo/greenkeys