1. TNC-220
2. MFJ-1278
3. G3RUH
4. MFJ-1270/1274
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!
2. MFJ-1278 19200 Baud serial rate
This modify allow you to set serial data transfer rate of TNC MFJ-1278 at 19200 Bd. For this purpose the 300 Bd serial rate will be lost. This modification does not affect the radio baud rates.
Extract IC U30 from socket. Carefully fold up (full) the pin 2. Put back in your socket (except pin 2). Install an insulated jumper wire from the pin 2 of IC U30 to the pin 10 of IC U1. Be careful not overhead IC,s while soldering, particulary U1. U1 - 4040 ; U30 - 4066 These IC,s are near the 12V plug. After this modification the serial data transfer rate selectable will be: 19200, 1200, 2400, 4800, 9600 To reconfigure MFJ-1278 serial baud rate at 19200: a) In terminal mode, set AUTOBAUD ON b) Power off the TNC c) Set the terminal program serial baud rate at 19200Bd d) Power on the TNC and push the RETURN key until the TNC sign on e) Set AUTOBAUD OFF
73 de Toni EA3CSX @EA3MM.EAB.ESP.EU - @KO23 - CIS 70630,1770
3. 19200 Baud Serial/Radio Port Modification for G3RUH Modem
Re: Looking for 19,2 Mod #ve8dx08.03
The following is a relatively easy modification that allows reliable 19.2 K baud on the serial port and radio port of most TAPR TNC-2 boxes.
***** FIRST AND FOREMOST *****
Replace U3 (LM324 op amp) with a TL084CN or TL094 if no TL084CN or eqiv. This is a high speed JFET hi-Z op amp. Just that fix alone will allow you to run 9600 baud on the serial port to your computer. I found that the TAPR 1.1.6. code WITH the PMS ran without any serial port misbehaving BUT it was sluggish. The 1.1.6. code (or lower) without PMS is quite a bit quicker.
***** 19.2 K *****
Cut the PC trace that goes to pin 2 of divider U1 about 1/8" from U1. Run a short jumper from pin 10 of the divider U1 to the side of the trace you just cut that goes to the SW2 baud rate switch. This is the side of the cut opposite to pin 2 on U1. This supplies a 307.2 K clock to pin 1 and pin 6 of the SW2 which NO LONGER SELECTS 300 BAUD.
The 307.2 K is 19.2K/16 which is fine and dandy. To run 19.2K on the serial port, turn SW2 switch 1 on. SW2 switch 6 selects 19.2 K to the MODEM port, switch 7 selects 1200 baud to the modem port and switch 8 selects 9600 baud to the modem port.
( keep in mind to leave switch 7 on unless you have installed a higher speed modem in your TNC )
We are running 19.2 K serial and 9600 baud radio with G3RUH modems and kantronics DVR 2-2 radios with excellent results. Next step is to up the G3RUH boards to 19.2 K by replacing a couple of capacitors.
OHHH WHAT A FEELING.......
de Anthony Varga VE3ZAV Kellogg Canada Inc London, Ontario, Canada 519 455 9660 Vmx 367 519 681 1650 Home
4. MFJ 1270/1274 19.2Kb Serial Port MODIFICATION
The following is a simple modification that allows reliable 19.2 K baud communications on the serial port and 9600 baud on the radio port of the MFJ 1270/1274 and most other TAPR TNC-2 clones. (9600 baud radio rate only possible with suitable internal or external modem connected to modem disconnect header). 1. Replace U3 (LM324 op amp) with a TL084CN or TL094. The TL084CN is a high speed JFET op amp which will allow 19.2 kbaud on the serial port. If no other changes are made a serial rate of 9600 baud is now possible, continue below for 19.2kb serial rate. TAPR v1.1.7b or v1.1.8 firmware is recommended, problems have been reported with firmware containing PMS and mailboxes and also firmware programmed on 'slow' EPROMs. 2. Cut the PCB trace that goes to pin 2 of divider U1 close to U1. Run a jumper from pin 10 of the divider U1 to the side of the trace you that goes to the SW2 baud rate switch. This is the side of the cut opposite to pin 2 on U1. This supplies a 307.2 K clock to pin 1 and pin 6 of SW2 (307.2 = 19.2K/16). NOTE SW2 NO LONGER SELECTS 300 BAUD. Serial Port Baud Rate +++++++++++++++++++++ SW2 switch 1 on 19.2Kb (NOTE: 300 baud selection deactivated) SW2 switch 2 on 1200 baud SW2 switch 3 on 2400 baud SW2 switch 4 on 4800 baud SW2 switch 5 on 9600 baud (Note: 9600 baud packet is possible with a terminal rate of 9600 baud but the buffers fill very quickly. 19.2Kb serial rate is highly recommended) Radio Baud Rate +++++++++++++++ SW2 switch 6 = 19.2Kb SW2 switch 7 = 1200 baud SW2 switch 8 = 9600 baud Therefore the recommended settings for 9600 baud are SW2 1 and 8 on.
Mark Shepherd ZL1TRE, Auckland, New Zealand.