[GreenKeys] 33 ASR Troubleshooting - keyboard works in local mode but not line, etc.

[Jim Cooper]

On 20 Jan 2020 at 19:31, Thomas Moss wrote:

> I'm pretty new to this as it's my
> first time working on Teletypes, and
> I've only had these a few days. Any
> pointers as to what to look for would
> be greatly appreciated. I wouldn't
> be surprised if the non-standard
> features have something to do with
> it, and would be interested if anyone
> knows what the Olivetti parts are
> for. 

Here's my starting suggestions: 

An OHM METER is your friend !! 

Take the TU out of the circuit and use the 
ohmmeter across the line to the tty with 
no power on the M33... 

do you see a closed circuit?  (with resistance 
from the selector assembly) ...   

Press a keyboard key and rotate the motor 
by hand... do you see the ohm bounce open 
and closed as you turn the motor by hand? 
(if not, then use the ohmmeter to trace back 
to the keyboard contacts and figure out how 
to get them in series with the selector assembly). 

When you can see the keyboard contacts open 
and close the ohmmeter, then you can go back 
on the local loop. 

2) Make yourself a little 120vDC power supply with 
a 2k power resistor in series as a test local loop and 
use that in place of the TU until you get the machines 
working.  ( 2k is for 60mA loop; use 6k for 20mA loop). 

What power rating for the resistor?  Watts = Volts x Amps

120v * 0.20A = 24 watts    [for 20 mA loop]

You want to eliminate all possible problems from the 
TU until you get the machines working right on a plain 
old local current loop.