Friday, May 25, 2018

Found minor problems with Documation interface; started restoration of Teletype 19


One of the problems I need to correct is the mechanical interference between the header connector with the card reader signal wires and the mini USB cable. I didn't allow for enough room, thus the cable from the USB connector wants to run right through the side of the header connector.

USB cable interferes with header for card reader connections
My plan to correct this is to desolder the back row of the header that connects my USB board to the interface PCB, then tilt the board upward by pushing down the newly loosened header row and soldering. If it tilts enough, the USB cable can clear the top of my signal connector.

A minor flaw I discovered is in the wiring of the LED that indicates the End of File (EOF) circuit. I wired it between the output of my board and ground, but in fact it should be reversed polarity and wired between the output and +5V. That one was easily corrected.

I know my board is mainly working because when I power it up outside of the card reader, I can talk to it with the PC software over USB and see the EOF status changing as I toggle the pushbutton. It doesn't respond when installed, but I believe that may be because of the USB cable interference issue I covered up above. When the cable clearance is solved I will try again.


Today we helped Marc strip down his military version of the model 19 teletype in order to have all the painted surfaces sand blasted and powder coated to look like new. Much of it could be removed by unscrewing or unbolting, but there were more challenging areas. Some parts were riveted in place or have welded hinges.

The transmitter unit required quite a bit of unsoldering to remove all the parts before the baseplate and covers are repainted. We carefully marked all the wires before desoldering, in conjunction with pictures of the original connections.

The teletype came with a huge power supply (REC 30) which generates the power for the teletype signal line which is a 60ma current loop. The supply has enormous transformers and fuses appropriate for a supply of several hundred watts, yet a teletype current loop should need less than 10W. Later we realized that one supply would be used to power a room full of teletypes, such as in a newsroom.

The desk which is a base for the teletype as a very complex wiring on the back, with 13 power outlets of almost as many types of receptacles connected by a sea of wires. The teletype itself has two power plugs attached, the REC 30 power supply has input, output and motor power plugs, then there are a few switches under the tabletop.

Some of the power outlets and fuses on the back of the teletype desk

It will take us our next session to trace out and understand all the wiring to these outlets, since we need to remove all outlets and wires in order to send the desk out with the other external parts for repainting. I did find a wiring diagram on the web which appears to match the desk. 


  1. USB cables with right-angle connectors are available in several configurations - check out eBay and Amazon.

    I'm a little worried about Marc getting into military gear - he'll probably end up with a half-track in his driveway, after doing a tear-down and restoration on YouTube.

    1. Hi Jack

      Good idea with the right angle connectors - bought one and will check it out before I do anything more drastic. Clearance may still be a bit tight but if it works, this is easiest.

      Don't expect Marc to shift to military gear, it is just part of his teletype collection (model 19, this military 19, and two ASR 33 models).