[GreenKeys] AN/UGC-74(A) teleprinter

[Nick England]

Ray is a regular on the 850 shift net, sometimes running in the field from
his vintage Army M151 jeep

---------- Forwarded message ---------
From: Ray Fantini <RAFANTINI at salisbury.edu>
Date: Tue, Jan 2, 2024 at 10:08 PM

Ok, another opportunity for everyone else’s to show me just how much
smarter then me they are, usually that’s just left up to the wife to do.

For a year or two now I have been playing around with a UGC-74 (A)
teleprinter. To start off with I have used B and C variants before and
don’t like them because its beyond my capabilities to make a ribbon
cartridge work in them so I want to use a old A variant because that uses a
typewriter ribbon.  Well aware of the melting rollers and have addressed
all that thru hours of cleaning already. Several months ago did a bunch of
work on this machine. Had a blown switching device on the power supply card
and changed that and also discovered that many of the big electrolytic
capacitors on the power supply card were open and replaced them. At that
point I had a working power supply card providing all the voltages that
were called for on the schematic, all within limits with no noise or
anything like that.

The problem then was that the drum would not spin up; also faults would not
clear when you sent a reset. The lights on the front will come on and when
you hit the reset button they would go out but as soon as you release the
button would come right back on. I know if I drove the “Drum Stop” line low
to the power supply card the card would then start the drum spinning but as
soon as I removed the jumper it would spin back down. I can also see the
pulses from the optical pick ups on TP-2 and 3 on the A4 printer controller
card when its spinning. All three voltages on the A2 memory card test
points are good so assuming that the A1, A2, A3 and A4 card are all getting
power.

This project got pushed off to the side for a while because I thought that
maybe the CPU(A1) or the Print Control (A4) were defective but was loaned a
set of cards and swapping both make no difference. The manual alludes to
that when you turn on the machine the CPU (A1) enters a state where it
lights all the bulbs on the front along with sending a message to the Print
Controller (A4) and upon receipt of that message sends a signal back to the
CPU telling it to turn off the lights. Think it may also start the drum
motor at that time too. But that never happens.

Besides the power supplies and motor drives nothing else sappers to work
the manual line feed button works and am wondering if that need
participation of the CPU because it’s a multi pulse stepper motor? That may
indicate that the CPU (A1) is up but just not getting any love from the
Print Controller (A4)?

Open for any suggestions; do have other machines that I am using but maybe
because of brain damage or what ever want to have a UGC-74 to pair with
MD-522 and the GRC-106 in the mutt.



Ray F/KA3EKH


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