[FADCA] Help needed from all TNC-2 Experts

[bud Thompson]

(How  many are there out there?)

We have run across several MFJ TNC-2 clones (i.e. 1270c, etc, etc.) that
have zilch TX audio output at the 5-pin din to the radio.  Circuit tracing
indicates plenty of TX audio from the modem clear out to a 0.33 capacitor
coupling to Pin 1 of the 5-pin din.

 circuit looks like this:

TXA generator ---> 0.0047mfd->-7.5k resistor-> 0.33mfd->Pin1 5pin din.
                                                                        |
                                                                        |
                                                                  560 ohm
                                                                        |
                                                                     GND

That 560 ohm (swamping?) resistor to ground is really swamping the circuit.
Lift if off ground and there is plenty of TX audio.

Q. What is the fix?
Q.  Aww.. if you say remove the 560 ohm resistor - how did it ever work at
all?

bud N0IA