Try to listen on another Transciever, possibly a Hand Held Radio or monitor of some kind, and pick a clean freq. (simplex) with LOW pwr. This is helpful, but not required.
Enter this command from command mode: CALSET 438 or (n=525,000 / 1200 + 1) which in either case will equate to 438 or therabouts. This is your MARK tone CALSET number or 1200 Hz tone.
Remove the jumper from JMP 8 and place on JMP 9 Pins 1 and 6. (If you are facing your TNC pins 1 and 6 are on the far right).
Type CALIBRA or CAL. Hit the letter "K" and then the space key to get the lower of the two tones. NOTE: you may want to remove the jumper from JMP 5 to use on JMP4 to override the watchdog timer circuit.
Adjust R-78 until the you hear a change in pitch of the transmitted tone, AND both the CON and STA led's light up and stay lit, or at least alternate back and forth the same rate. Ideally, they should both stay lit simultaneously.
Hit the "K" again, and then "Q" (to quit calibration) and then go back to CMD: mode.
Give the TNC the command: CALSET 239 or (n= 525,000 / 2200 + 1) which equals a CALSET number of 239.
Repeat step 7. Repeat step 8, but adjust R-77. Repeat step 9.
NEXT - REMOVE the jumper from JMP 9 (Pins 1 and 6) and place the jumper on Pins 2 and 5. - the center two pins of JMP9.
Go to CMD: mode and type this: "CALSET 157" or (n= 262,500 / 1685 + 1) which would equate to a CALSET number of 157. This is your Demodulator/or center freq of 1685 Hz.
Repeat step 7, this time adjusting R-79 for the best condition of the CON and STA LEDs (both lit at same time).
Replace JMP 8 (from JMP9) and replace JMP 5 (from JMP4).
Once you have done all of the above, you have successfully calibrated the TNC's tones. LAST BUT NOT LEAST...follow the MFJ or TNC 2 Manual on how to properly set the deviation level adjustment (R-76) so that your transmitter puts out in the neighborhood of 2.8 to 3.0 kHz of deviation.