Tune-up directions and notes for MFJ 1270/74 TNC

The directions for calibrating the tones on an MFJ 1270/74 leave a lot to
be desired.  Here is what MFJ forgot to tell you.

The procedure is different for modulator (transmitted) tones than for 
demodulator (received) tones.

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CPU clock

Connect a frequency counter to pin 6 of U 10 or loosely couple the antenna of
a calibrated communication receiver to this same pin and adjust C 47 for 
4.9152 Mhz  +/- 100 Hz.  This adjustment is not critical for TNC operation
but it is for accurate tone calibration.

The position of JP 2 (CPU speed select) is irrelivant to the calibration
procedure.

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Modulator tones

1) Install a jumper from pin 1 to pin 4 on JP 9.  These are the two pins 
   on the six pin header nearest to C 44

2) Enter the CALSET number from the list below.  "CALSET 439" for 1200 Hz.

3  Put SW 3 in the proper position. (HF or VHF)

4) Enter the calibrate mode by typing "CALIBRA"

5) Type "K" to key the TNC. (you should not have the tranceiver connected)

6) Listen to the output audio to determin if the TNC is sending the high
   or low tone of the selected pair. Tap the space bar to toggle high/low.

7) Adjust the pot. for that tone given in the list.
        Note if the tone frequency is low  the "CON" LED will be on.
             if the tone frequency is high the "STA" LED will be on.
             both LEDs on or alternating between "CON" and "STA" tells you
             the tone frequency is close enough.

8) Type "Q" to quit the calibrate mode and repeat to step 2 for the next tone
   to be calibrated.  You should calibrate all four modulator tones, but 
   you may wish to calibrate only the VHF or HF pair.  You should do both 
   tones of the selected pair.

9) Remove the jumper on JP 9 installed in step 1.  This completes the
   modulator calibration. 


  TONE     FREQ.    POT.    CALSET #     SW 3 Pos.
HF  MARK   1600 Hz  R 106     329          IN
HF  SPACE  1800 Hz  R 105     293          IN
VHF MARK   1200 Hz  R 78      439          OUT
VHF SPACE  2200 Hz  R 77      240          OUT

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Demodulator tones

1) Install a jumper between pin 2 and pin 5 on JP 9.  These are the two
   center pins in each row of the six pin header.

2) Enter "CALSET 155"  Do NOT enter the CALIBRA mode! 

3) Put SW 3 in the "VHF" (out) position.

4) Adjust R 79  and watch the "CON" and "STA" LEDs.
            Note the "CON and "STA" LEDs react the same for demodulator tones
            as for modulator tones.  (See step 7 above)

5) Since there is only one adjustment for the demodulator, remove the jumper
   installed in step 1.  This completes the demodulator calibration.

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IMPORTANT NOTE FOR NETROM AND OTHER NETWORK USERS

You MUST remove the special network ROM chip and insert the original MFJ ROM
and be sure that there is no connection to pin 23 of the RS-232 connector.