[FADCA] Re: Help needed from all TNC-2 Experts

[Chuck Hast]

On 10/15/06, bud Thompson <budt at cfl.rr.com> wrote:
> (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.
>
I wonder if the .0047 is bad and passing less audio, or the load on the
TNC is higher than expected? Is there any audio with no load on pin1 of
the din?


-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."