MFJ MFJ-1270X User manual

TNC-X Packet Controller
Model MFJ-1270X
INSTRUCTION MANUAL
Digipeater Daughter Board below ...

Introduction
Thank you for purchasing the MFJ-1 70X TNC-X Packet Controller. The MFJ-1 70X
is a new Terminal Node Controller design based on the Chepponis/Karn KISS pro-
tocol. It is implemented using a Microchip PIC 16F6 8A microcontroller, a CML
MX614 Bell 0 modem chip, an 8k Ramtron FRAM, a MAX 3 A level converter
chip, and an op-amp which provides active audio filtering for the modem. From
the beginning, this TNC was designed to be small, inexpensive, have low power
consumption, and expandable.
The MFJ-1 70X features an on-board USB port. The USB port was added because
the design took into consideration that computers these days lack the old style
RS- 3 serial ports. There is also an 8-pin expansion header that allows the addi-
tion of "daughter boards". Power is provided to the daughter board through the
expansion header. In addition, signals that would otherwise go to or from a host
PC can be intercepted by the daughter board at the TTL level and processed. The
I/O on the expansion header speaks "KISS" so that any daughter board only has
to send and receive data packaged in KISS format to access the core module.
This makes the development of daughter boards fairly simple and inexpensive.
For example, daughter boards are now available that can turn the MFJ-1 70X into
either of two types of digipeaters, or into a stand alone APRS Tracker.
In addition, the expansion header provides access to a second on-board serial
port. The X-Track daughter board, for example, uses this port to receive data
from a GPS receiver. The data is then processed and formed into packets and an
APRS beacon is sent. Even without daughter boards the MFJ-1 70X works as a
fully functional stand alone KISS mode TNC.
The idea behind the expansion options was to provide a platform that would al-
low additional functionality to be added to the unit with the investment of very lit-
tle design time and very few parts.
Power Requirements
IMPORTANT: DO NOT PLUG IN THE 8-15 VDC POWER SUPPLY AND THE 9-VOLT
BATTERY AT THE SAME TIME!
The power requirements of the MFJ-1 70X are very minimal due to the low pow-
er consumption of the design. Using an 8-15 volt DC power supply capable of
00-300 mA is well within the consumption specifications. There is also a 9-volt

battery snap provided for a 9-volt battery. This makes the TNC more portable for
campers and backpackers.
Terminal Speed
The MFJ-1 70X supports only 4 terminal speeds. Jumpers JP1 and JP determine
the speed strictly for the link between the TNC and the computer. The following
settings are allowed:
JP1 JP2 Port S eed
On On 1 00 baud (default)
On Off 4800 baud
Off On 9600 baud
Off Off 19 00 baud
Note that the terminal speed setting does not affect the speed to transmit data.
The out-going or transmit speed is always 1 00 baud. Note also that if you set
this baud rate faster than 1 00 baud, it is possible for data to be fed into the mo-
dem faster than it can transmit it over the air. This may eventually result in the
transmit buffer filling up.
Setup If You Are Using USB
If you have elected to use the USB port to provide data communications to your
PC, you should begin by acquiring and installing the drivers for the PC and operat-
ing system that you are using. The driver you need is a Virtual Com Port (VCP)
driver. It will make the TNC appear as an additional com port on your computer
so that you can use any packet radio software that supports a KISS TNC connect-
ed to a standard serial port.
If you use the USB port, do not supply any power to the TNC through the power
jack.. The USB buss can supply the rather limited power requirements for the
TNC. If you are using the MFJ-1 70X Instruction Manual TNC-X Packet Contoller
5 USB option, set the board jumpers as follows:
JP3 On the left two pins (toward C 4)
JP4 Connect the center pin to the pin that is closest to the center of the
board.
JP5 Jumper pins 1 and (the end closest to Q1) and pins 3 and 4, unless
you are using a daughter board.

Setup If You Are Using the TNCs Serial Port
If you plan to connect the TNC to a standard computer serial port, set up the
jumpers as follows:
JP3 On the right two pins (toward U5)
JP4 Connect the center pin to the pin closest to C .
JP5 Jumper pins 1 and (the end closest to Q1) and pins 3 and 4.
If you are using the on-board serial port, you must supply power to the TNC. This
can be done in one of two ways. There is a coaxial power jack on the board that
can be used to receive anything from 8 to 15 volts DC. Alternatively you can con-
nect a 9-volt battery to the location marked BAT.
Aux 232
An auxiliary serial port using a MAX 3 level converter. Main purpose is for GPS
input for the X-Track daughter board.
Serial Port
A standard DB 9-pin RS- 3 C serial port.
USB Port
A standard USB port for computers that lack the old style RS- 3 serial ports.
Power 12VDC
A coaxial power jack for main power input. Center pin is positive and sleeve is
negative.
RADIO
A 5-pin DIN connector used to interface the radio to the TNC.

POWER
Indicates the MFJ-1 70X has power supply voltage supplied.
RECEIVE DCD
Indicates the MFJ-1 70X is receiving a data packet signal from the radio.
TRANSMIT PTT
Indicates that the MFJ-1 70X is transmitting data signal from the radio.

Radio Setup
The radio connections are made via a 5-pin DIN chassis mounted connector. The
connector is shown below:
Back View of Connector
Radio Port Connections
These are the radio port pins and their respective functions. Match the proper pin
and its function to the same pin and function on your radio.
Pin 1 – Microphone Audio: Supplies audio from the TNC to your radio.
Pin – Ground: Common connection for audio and PTT common.
Pin 3 – Push-to-Talk: Allows the TNC to key your transmitter to transmit.
Pin 4 – Receive Audio: Supplies audio from the radio to the TNC.
Pin 5 – No Connection
Troubleshooting
The MFJ-1 70X is designed to give years of service. However, as with all things
sometimes problems do come up and need to be taken care of. Here are a few
troubleshooting tips in the event that something does go wrong.

Voltage Supply
If the supply voltage is suspect this must be corrected first. The first thing to do
is to check the main voltage supply to the TNC. Do this using a DC voltmeter ca-
pable of measuring +5 volts DC. The main supply voltage to the TNC must be at
least 7 to 8 volts DC. The TNC uses a 78L05 voltage regulator. The voltage regu-
lator needs to see a voltage at least volts greater than the regulation voltage. If
the main supply voltage is not volts greater than +5 volts, then the regulator
will not work, thus not having a +5 volt DC output. To check this, do the follow-
ing:
1. Set your voltmeter to read +5 volts DC.
. Remove the main supply from the TNC. Check the voltage at the connector
that plugs into the TNC. The voltmeter should indicate +5 ±0.5 volts DC. If
the reading is lower, then check the main power source. If the reading is
good, then move on to step #3.
3. With the main power still removed from the TNC, carefully remove all IC
chips from the TNC.
4. Reconnect the main power source into the TNC and re-check the +5 volts
DC.
5. If you are using the computers USB port to supply voltage to the TNC, meas-
ure the voltage between ground and the right pin on JP4 or the right pin if
you use power jack. It should be approximately +5 volts DC. If not, then we
strongly recommend returning the TNC for service. If the voltage is good,
then move on to the next section.
Testing for Defective IC Chips
If you are reading this section, it means that you have determined that your TNC
has a defective IC chip. The procedure for checking for a defective IC is not com-
plicated, but you should follow the procedure carefully. If you do not follow the
procedure carefully you can and probably will damage an otherwise good IC
and/or the TNC…so please be very careful.
1. Remove power from the TNC, either by removing the main supply at the
power jack or the USB port cable.

. Carefully remove all IC chips from the TNC. Make note as to the orientation
of each IC in their respective IC sockets and which sockets the ICs came out
of. Be careful not to bend any of the pins of the ICs. IMPORTANT!
3. Carefully re-insert one IC at a time into its respective socket and recheck the
+5 volts DC. If any IC causes the +5 volts DC to drop, then the IC that caus-
es the voltage drop is your defective part. Be sure to check all IC chips, be-
cause you could have more than one defective part. Call the MFJ Service
Dept. for a replacement part.
Testing Receive
Hook up a receiver audio source to the receive pins on the board (or the mono
jack if you are using the enclosure). Make sure audio goes to the positive pin.
Make sure the squelch is left open. When a data packet is received, you should
see the yellow LED light briefly and go out. Even when no data is being received
it is normal for the yellow LED to flicker. However, it should come solidly on when
a packet is received. Assuming that this checks out, run a serial program of some
kind on your PC, set the baud rate to whatever baud rate you specified with JP1
and JP . Confirm that you are receiving data (note, this will be raw KISS frames
so much of it may look like garbage, but you should see some recognizable data).
Note that if you are using the USB option, you must the USB drivers loaded on
your computer.
If you do not see the yellow light come on, first confirm that audio is getting to
the TNC (a scope or a small headphone may be useful for this). If it is, verify that
audio is coming out of Pin 6 of U4. Assuming this is working, if you have a scope
or frequency counter, measure the frequency on Pin 1 of U1. It should read about
3.57 MHz. While you are at it, check Pin 16 of U3. It should read about 0 MHz.
If at any point you don’t get the measurement you expect, carefully check the
solder joints in that part of the board. If the yellow light comes on but you see no
data on your PC, start at Pin 8 of U3 and trace the data signal to header Pin 1, to
header Pin and on to Pin 10 of U5. It should come out at Pin 7 of U5.
Next check out the transmit chain. The TXDelay is set by R13. Start by setting it
at about halfway (which will correspond to a TXDelay of about 40 ms (or a set-
ting of 5 on most TNC’s). At this point you need to be running a program on
your PC that supports KISS mode. The TNC-X webpage (www.tnc-x.com/docu-
mentation.htm) has a program called TXTest, which is a very simple program that
can be used to test your transmit chain.

When you transmit a packet, you should see the red LED come on briefly. Hook
the transmit audio and PTT up to a radio and try transmitting. R1 is used to ad-
just the transmit level. If you don’t have a means of measuring the deviation pre-
cisely, monitor your signal on a receiver and slowly increase R1 until you hear no
further increase in volume on the receiver. Then back it off a bit. Even if the TNC
is not connected to a radio, you should see the red light come on when you
transmit data via the TNC.
Many people use TNC-X for APRS applications. There are many good software
programs available for this application (WinAPRS, UI-View for Windows, for exam-
ple). For a general purpose TNC program that supports KISS, you might want to
take a look at WinTNC. It has recently been revised so that it works under Win-
dows XP, as well as older versions of Windows. If you want to use AGWPE, there
is a link on the TNC-X webpage that contains detailed instructions.
If you have any problems with any of this, please contact MFJ Technical Services
at the phone number in the warranty instructions.