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After finally getting my Lo-15b cleaned up like new and lubricated, I connected it to the call control unit.
Press the LT buton, the LT lamp comes on. The motor starts and the machine waits for me to type. (The loop is closed)
I type and nothing happens. It acts like the keyboard is shorted.

As a test, I disconnect the Lo-15b and wired it up to an external 120 vdc source with a series resistor to limit the current to 40 mA.
That works. I type, it prints.

Then I connected the Lo-15b directly to the TW39 port on the i-Telex interface.
Press LT to turn the motor on, Machine comes up and idles as it should (The loop is closed)
But again, I type and nothing happens. Or I use the "Send Message" function on the i-Telex web interface.
It doesn't receive anything nor does the keyboard send anything.

This is really frustrating, everything was working perfectly five years ago.

Jeff

Hi Jeff,
The LT button means Local operation.
What Happens when you press the AT button?
Fred

Correction, this morning when connected directly to the i-Telex box, now the keyboard works. I type, it prints.

However, while connected to the call control unit, pressing LT brings up the machine, the loop is closed, but it ignores the keyboard like it was shorted.

When I press the AT button, I hear a relay in the call control box go click. The AT lamp doesn't go on. The dial remains locked.
If I press the ST button, the AT lamp flashes briefly,and goes out, I can hear a relay release.

As a side note: I successfully upgraded the i-Telex firmware this morning.

How did you connect the call control unit to the i-telex?
What kind of plug does the unit has?
Have you applied a wire from pin 2 to 3 resp. from b to W2?

Regarding the function of the LT button, there is indeed something wrong...

Heinz provided me with a handful of the 4-pin plugs and jacks.
The i-Telex jack has a and c connected to the TW39 port, and a wire from c and W2 as it should be.

And yes, there is something wrong with the LT (local) function.

Fat fingers.
The i-Telex jack has a and b connected to the TW39 port, and a wire from c and W2 as it should be.

That's wrong

a and b = transmitter contacts
w2 and c = receiver magnets

jumper between b and w2

line (i-Telex) to a and c

I was doing that from memory.
I went and looked at the connector.
Line = a and c, jumper b and W2.

Please use a volt-meter to measure the voltage from i-Telex and from the control unit to Lo15. Polarity is important. Measure in idle mode and in local mode.

16 v, + on c - on W2. When connected to the i-Telex box.
14 v, + on c - on W2. When connected to the call control unit in LT (Local) mode.
Measured at the terminal strip on the side of the Lo-15b.