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

Sun, 4 Apr 2004 14:25:22 +0100

Hi Carl,
		I don't have a PK-88 manual here anymore, so Unfortunately I can't 
check the circuit diagram.
PIN 12 is associated with the input line going to PIN 13. Can you check 
where PIN 13 on the IC4 goes to, I imagine one of the DB-25 pins.

This will tell us whether it is the Receive data line or possibly a 
hardware handshake line.

It may be that your modem cable is missing a line going to that input 
and by putting a probe on teh threshold input you are simulating the 
effect of having an input on that pin 13 by changing the threshold at 
which pin 13 changes state.

73

David
On 4 Apr 2004, at 1:56 pm, Carl Miller wrote:

> Hi David and All,
>
> I am using a DB-25 to the Apple 8 pin connector to
> connect the tnc to the Mac. I believe it's a standard
> Apple modem cable and I have it connected to the modem
> port.
>
> My terminal program is Microphone. It came with a
> Supra modem I bought and I noticed it mentioned in the
> PK-88 manual as one of the programs tested with the
> tnc. It works great as long as I'm touching pin 12 of
> IC-4 with a probe of some kind.
>
> My settings on the terminal program are:
>
> 1200 bauds
> 7 bits/character
> even parity
> handshake- xon/xoff
> modem connection- telephone port
> 1 stop bit
> the only function I can't set according to the manual
> is "full duplex". I don't see that setting in any of
> the Microphone menus.
>
> By the way, and I forgot to mention, when I first
> discovered this unusual procedure I thought perhaps it
> was a bad IC socket so I removed IC-4 from it's
> socket, removed the socket, and soldered the chip
> directly to the PCB. It didn't help.
>
> If you need any further info just let me know. This
> thing is really got me confused.
> Thanks again,
> Carl
>
>
> --- David Anderson GM4JJJ <[email protected]> wrote:
>> 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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