Friday, June 15, 2018

Teletype stuff


Marc disassembled the entire Model 19 teletype, separating all the painted metal parts for restoration. This military unit had been repainted by brush and was quite ugly. The plan is to strip the old paint off and to powder coat the unit to make it appear like new.

We drove it over to the shop to get a quote and to let Marc pick out the color and finish. The price itself was quite reasonable and the staff were clearly able to protect threaded screw holes and other parts that had to stay clear.

Marc is wavering between a blueish-green color and a flat black, but part of the decision depends on the quality of the metal once it is sandblasted clean. If too many scratches and dings, it will need to be a more textured black color to hide imperfections. To the eye, most of the flaws we see are likely to be simply paint chips from all the layers of paint on the object.

The plan is to have the desk and the teletype printer cover sandblasted first, then Marc will come by to inspect the metal condition. Based on that, he will choose colors and have the shop continue to sand and then powder coat everything.


I brought my model 15 teletype, model ASR33 teletype and model 14 transmitter/distributor over to Marc's house to join his model 15, model 19 and two ASR33s for restoration. I tore the ASR33 down to separate the printer unit, keyboard unit, call control unit, stand and cover, in preparation for restoration.

The baseplate had foam rubber as a sound dampener, but the material had become friable and partially disintegrated. For the most part it did not become liquid and stick to the baseplate, which made cleanup relatively easy. Only the spots where adhesive was used to tack down the foam will take additional work to clean up.

While I was moving my model 15 printer unit around in my garage earlier this week, the work gloves I had on snagged onto a spring on the side of the printer unit and released it. I needed to search for the spring in the garage, but first it was important to know where it was formerly attached.

Using the model 15 at Marc's house as a guide, I identified every spring on the left side of the printer unit and matched against my unit, thus locating the missing spring. It attaches to the carriage return dashpot arm, to restore the dashpot which is an air dampener that absorbs shock from the carriage slamming to the left edge.

Dashpot restore spring, missing on my model 15 printer
The arm will push into the dashpot, converting carrier motion to air compression and spreading the deceleration over a longer interval to minimize G force. The carrier rebounds to the column 1 position and the spring then pulls the dashpot arm out to ready it to handle a subsequent return. I found the spring in the garage where it was pulled off by the glove.

My ASR33 keyboard is not working properly. Each keypress should set the sliding rods to reflect the ASCII code related to the character on the keycap. Lubrication has hardened and gummed up the works a bit. I worked the mechanism, cleaning off old grease and inspecting the condition. 

ASR33 keyboard module
Now I see every character encoding properly on the switch contacts on the side of the keyboard, but I am not happy with the trigger and release that fires the distributor to serially encode the result of a keypress. The keypress pushes on the universal codebar, which trips for every key. I don't see it trigger and then restore properly between button pushes. I will study the mechanism and manuals, then adjust whatever is needed until the keyboard works as it should. 

No comments:

Post a Comment