[Ham-Mac] Need help with PK-88 TNC

[David Anderson GM4JJJ]

Carl,
		Can you tell us the details of how your serial lead is wired? Also 
what software, is it a regular terminal program like ZTerm or what?

73
David



On 4 Apr 2004, at 1:15 am, Carl Miller wrote:

> Hello All,
>
> I am new to the list and I already need help with a
> problem.
>
> I have a PK-88 TNC that I am trying to use with my old
> Macintosh Classic II.
>
> The problem I am having is that the PK-88 will not
> accept commands from the terminal. That is, until I
> touch a probe or other metallic object to pin 12 of
> IC-4, a 75189 quad line receiver. Once I power the
> thing up and touch a metallic probe to pin 12 the
> thing works great, I can send it commands, I can do
> the loopback test with no problem. But once I remove
> my probe, the thing goes deaf again. I also noticed
> that if I remove the probe, then touch pin 12 again it
> gives me the cmd: prompt. Then I can communicate with
> the tnc again.
> According to the Texas Instruments data sheet on this
> particular chip, pin 12 is the threshold control pin.
> But, since I am not an EE, I don't have a clue what
> that means. The funny thing about pin 12 is that it
> isn't connected to anything from what I can tell. It
> certainly isn't noted on the schematic.
>
> What gives here? Is this thing posessed or what?
>
> I would certainly appreciate any help or advice.
> Thanks in advance,
> Carl KA5KAB
>
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