[Milsurplus] AN/UGC-74(A)

[Ray Fantini]

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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