Pac-Comm TNC-220


Pac-Comm TNC-220 Manual (Manual also covers other model of the Pac-Comm TNC range)

Allow full duplex at 9600 baud

Hello All @ AMSAT

The following modification to the 220 will allow your Tnc to operate at
9600 bauds in Fullduplex. For those of you who thought you already could I
suggest you try it.
It must be mentioned at this stage that the version of my 220 is 1.3. If
yours is a different version then the story may be different, but I doubt it.

The reason for this mod is to allow my station to operate on UOSAT3 FULLDUPLEX
Previous to this mod I have been ripping my hair out as to why I could not
digipeat via UOSAT3. When one day I discovered that when I changed the
baud speed to 9600 and then put Fullduplex on the txbaud rate changed back
to 1200 whilst the rx rate remained at 9600. Most perculiar I thought.
So, I got in communications with the main Agent in the UK for Pac-comm to
see if anyone else had this same problem. No came the reply, obviously no
one else has tried it yet I thought. So here I am stuck with a TNC that is
no use to me for UO3. Can you help me then please I asked Agent. Yes we'll
see what we can do. In the meantime Rep has been to Paccomm across the pond
and I am told that they work alright over there. Cant be I said!
So anyway he suggests I try changing the thirmware which I did but still no
good. Ok we'll send them another Fax they said. Fine!
Another phone call to Agent 2 weeks later, no info or reply.
So I put pen to paper and addressed the same question to the Gentleman
concerned at Pac-comm. To date Ive no reply, letter sent some 4 months ago.

Not impressed!

With UO3 software now on release, and uploading and testing of UO3 bulletin
software imminent I figured I had better do something. The result is a
crued cure.

              9600 FULLDUPLEX on the Pac-Comm TNC-220
                  by D. Hulatt G4WFQ 19th Aug 90

      Locate 74HC4020 and remove from IC socket

      CAREFULLY bend pins 1 and 12 up

      Solder flying leads to pins 1 and 12 on 74HC4020

      Solder flying lead to pin 12 on SIO 8530 chip

      Use a SPDT switch to switch to 2 signals from 4020 to SIO

      Replace 4020

      Drill 1/4 inch hole in rear plate above RS232 slot

      Insert switch and secure.

      Thats it. Throw switch for 9600 FULLDUPLEX operation, revert for
      normal. NB: You still have to change buad rate in s/w.

I hope this information will be of use to some. I would like to thank
Uk Agent for trying to get info from Pac-Comm. It must be like trying to
get blood out of a stone.
Thanks Pac-Comm, no need to bother now I've done it myself!

73 de Dave G4WFQ @ GB7PET AUK.2404 19 Aug 90

Updated firmware / EPROM for the Pac-Comm TNC-220

None known to be online. If you do have a copy, please let me know.