billdeg
Technician
Just curious if anyone has ever replaced the 108mfd 125v motor cap on their ASR 33 TTY to successfully fix the problem of the machine not being able to exit "chatter" mode, an incomplete current loop. In my case the fuse is OK and the keyboard is mechanically OK. Voltages in the call control unit are ok. The CCU card solder joints are ok. The 20/60 mA current loop resistor is ok. With nothing else to try/fix I went ahead and ordered a replacement cap from an HVAC supplier, should be about the same type of thing as specs for engaging the TTY motor. It's pretty obvious the cap is bad, I am only getting 26V rather than a range of 95-120v depending on the motor load. I did not even notice the cap was there, until I removed the brown protective flap covering it. It's next to the rear fuse. The wire from this cap leads to the TTY motor.
I know mechanically the TTY will enter local mode because if I stick a 1/2 clothes pin in the catch of the "thingy" that latches the "thing" that causes the chattering, I can disengage it.
Here is a pic, just to the right center of this picture there's a little metal flap you can wedge open with a wooden clothes pin
http://vintagecomputer.net/teletype/ASR33_sn256219/teletype_ASR33_rear-right-1.jpg
Anyway, if I am correct others with teletypes that do not go into local mode or respond to a computer sending a 20mA current could also have a bad cap, check it!.
I know mechanically the TTY will enter local mode because if I stick a 1/2 clothes pin in the catch of the "thingy" that latches the "thing" that causes the chattering, I can disengage it.
Here is a pic, just to the right center of this picture there's a little metal flap you can wedge open with a wooden clothes pin
http://vintagecomputer.net/teletype/ASR33_sn256219/teletype_ASR33_rear-right-1.jpg
Anyway, if I am correct others with teletypes that do not go into local mode or respond to a computer sending a 20mA current could also have a bad cap, check it!.