[GreenKeys] TTY-connect

[Nico de Jong]

Hi greenkeyers

I need a bit of help with Gil Smiths TTY-connect. I have built about 7 of 
those units on Eurocards, but this one pulls my hairs out.
The problem is in the current loop. The input is 100VDC, which I find on 
E52. After J50 I go directly to E54. I find the 100V again at the junction 
of E57/D52/DS52, but DS52 does not light up, indicating that no current 
flows, which is confirmed when I put a mA meter in J50
When I put a mA meter between pin 5 on the H11D2 and ground, I get 34mA 
(R57/R59 is not quite on the spot, but that is a lesser problem) and DS52 
lights up
In other words, how come that the MJE340 blocks the current?
Which voltage should be present at the base of MJE340 to make it conduct?

How can I check whether the MJE340 or the H11D2 is defective?

I tried to put +5VDC on pin 1 of the H11D2 to see whether I could force Q50 
into conducting, but to no avail.
I'm sure its only a small problem, but I just can't see what is wrong, and I 
would appreciate your help.

For your information, the project calls for 5 of those units, to be 
installed at the danish Cold War museum. I was asked to install at 
PC-controlled telex exchange with 5 teleprinters (all Siemens T100), plus a 
connection to an encrypted system with 2x T100Z/M190, so people can see the 
effect of encryption.

Thanks
Nico 

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