Friday, July 13, 2018

Progress on model 15 printer and other teletype news


I need one replacement part for the paper tape punch on my teletype, but the spares part specialists at RTTY Electronics don't have one. I did see an eBay auction of a perforator, which is the tape punch unit from a model 33. The seller allowed me to make an offer and we agreed on a relatively low price which will give me the spare part I need. 


I began again to work on the model 15 printer, to free up the clutch trigger and stop for the mechanism that is spacing the carrier, since it is frozen and causes the carrier to drift steadily to the right margin. 

There is a rod that the function bar and other parts rotate around, including the trigger and stop levers for the spacing mechanism. Those two levers were frozen in place. I decided that I had to remove the rod from the printer to get access to the frozen levers. I had to remove some springs and detach the function mechanism which drives operations when the five code vanes match the code for a function such as CR.

Frozen levers down inside the printer mechanism
After removing the rod and related parts from the printer, we could move the lever slightly by striking it with a hammer. We removed the bolts holding the rod in its frame, then tried to drive it out of the parts to clean things up. We could get it to move about a millimeter in either direction with a fairly hefty hammer and wood blocks, but no more.

Rod with frozen levers, plus function plate above
We clamped the whole mechanism down, dripped in very fine clock escapement oil, and hammered the levers to make them rotate. At first it took a wood block and hammer, but after about 30 minutes we could move them by hand, albeit very painfully. These parts should rotate easily and snap back under spring tension. 

Main shaft visible with the function rod removed from machine
Ed Thelan took over, judiciously adding clock oil while relentlessly moving the levers over their range of motion until they were fully loosened. This took him about an hour of stubbornly twisting the parts. At this point, we had to end the workday but everything is ready to reinstall and after some adjustments, the printer unit should be working. 

Bob Erickson's model 15 is a governor model, whose motor speed is adjusted by the technician. We used a box to drive the unit with 60ma 120V at 45.45 baud but the text being printed was somewhat garbled. Today we decided to adjust the motor speed, since it must be the right speed to decode the incoming data stream. To our surprise, the motor didn't start at all when we plugged it in.

We discovered a broken wire, which was fixed, and another wire which was hanging on by its last strand. Now it works again. The workday ended, but our plan when we resume is to hook up the SEND contacts to the oscilloscope and adjust the motor speed until the bit cells are exactly 22 ms, which corresponds to 45.45 baud. After we know the speed is right, we can test the printer again. It may be sludgy and require some TLC, but perhaps it is simply a matter of adjusting the speed. 

Marc picked up the powder coated metal parts for his model 19 teletype - they look fantastic. We now have to put everything back together; 39 coated metal parts and the many hundreds of other parts that go inside. 

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