[GreenKeys] Model 15 wiring help

[John Lawson]

Greetings GreenKeys!


I've had my share of teleprinters over the years, starting with a model 
14 I got in 8th grade, with a highly modified IBM typewriter controller 
that punched and read 5-level tape - a story for another time...

I am helping clear out an enormous collection of Stuff for an elderly 
gentleman who can no longer deal with heavy electronica. This collection 
is actually over the boundary into hoarding - there is over 4000 ft^2 of 
Stuff.

There is a good deal of TTY peripheral gear, and a Model 26, a Mod 15, 
and an ASR33.   I sold the 26, got the 33 running pretty much, and have 
begun work on the 15.

It sat in covered storage for probably 25+ years, so of course all the 
lubricants changed to stiff goo, mice explored it (but did no damage 
other than their excreta), and it was pretty dusty/dirty.

I've got the mechanical side working okay, a few issues remain but 
they're fixable.

I'm having problems figuring out the wiring - I never paid much 
attention to the wiring before, as all my previous machines had cordsets 
and connectors; plug 'em in and type.

This particular Mod 15 is a Bell System unit, with the on-board polar 
relay, and what (i think) is a polar/loop lever-type keyswitch attached 
on a sideways bracket to the keyboard base.

The Base is a 15 D.

The Keyboard is a 15 A37

The Typing unit is a 15 Y.

The polar relay is a 255A


It came with the stubs of cut cable sets - I have wired 120 AC to 21 and 
23, a loop supply to 24 and 25, and a 9V battery to hold the polar relay 
closed to 41 and 42.

The loop supply is running at 110VDC, but only shows a draw of about 15 
mA. There are two side-by-side selector magnets, reading about 45 ohms 
and wired in parallel. The send/rcv/brk keys are constantly being reset 
to 'send' by the mechanism, but if the key is held the unit responds to 
it's keyboard, but badly - I imagine because of the low loop current. I 
have not yet tried to send baudot into the polar relay circuit, but it 
looks like that might have been the way it was used.

I have several schematics, including the military Model 15 TM. None of 
them are completely "correct" for this machine.

Before I go down any more rabbit holes, no matter how instructive they 
may be, I would like to ask for some advice/assistance/pointers to 
getting the electrical side sorted out.


Thanking y'all in advance, and reply off-line if appropriate. I'm 
looking forward to printing ITTY with a HAL ST-6000 that I'm also 
restoring....


Cheers

John KB6SCO

Carson City