SB-018

Service Notes on TR-7400A                             10-6-77

TRANSMITTER

1.   No meter indication but output power OK:  Check for broken wire at
     terminal SM1 on the RX Unit.

2.   Transmitter intermittent when keyed rapidly:  Defective D3 (MI402) on
     PA unit (X45-1090-10).

3.   Position of L2 in PA unit:  The proper position of this coil is
     directly on the collector tabs of Q2 (2N6083).  This applies to 45XXXX
     serial numbers only.

4.   Background noise on transmit:  Reverse coil L1 on the TX unit (X56-
     1230-10).

5.   RF meter works when first key transmitter an then fails:  Check for
     pinched RF sens wire at coil L7 in PA unit.  Widen this coil if necessary.

6.   Transmitter off frequency and receiver on frequency:  Adjust coil L3
     on TX Unit for correct frequency.

7.   No RF output:  Diode D3 (MI402) in PA unit shorted or improperly
     soldered.  If this diode is replaced, keep the leads as short as possible
     an build up solder on the foil side of the board.

8.   Low output power:  Loose connection at TC3 in PA Unit.

9.   No RF output and receiver sensitivity dow 30db:  Diode D2 (MI301) on
     the PA Unit may be defective.  Also check D3 (MI402) on this board.  Q1
     (3SK41L) on the RX unit may also be defective.

10.   Intermittent or no transmit:  Check for loose connection at Q15
      (2SC908) on the TX Unit.  Also check the heat sink for this transistor.

11.  No RF output but drive to PA Unit is OK:  Check for proper SB voltage.
     It should be 11 to 12 vdc when transmitteing into a 50 ohm load.  If it is
     0vdc check Q10 (2SC496) on the TX Unit.

12.  No Modulation:  Capacitor C4 (0.1 ufd tantalum) on TX unit may be
     open.

13.  No modulation:  Check for pinched pins at microphone jack.

14.  No RF output on one band:  Check for proper alignment of
     potentiometers VR61, 62, and 63.

15.  No RF output:  L4 not soldered to base of Q4 (2SC458B) in PA Unit.