SB-018

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

RECEIVER

1.   Receiver sensitivity down 30db:  Check voltage at the drain of Q1
     (3SK41L) on the RX Unit (X55-1150-10).  It should be 7 volts.  If it is
     "0vdc", check for shorted feet-thru capacitor in the helical resonator.
     It may be necessary to replace the helical resonator.

2.   No receive:  Check C9 voltage.  Q27 (CSC496) on RX unit may be
     defective.

3.   No receive and no C9 voltage:  Check Q28 (CSC496) and zener D16
     (WZ090) on the RX unit.

4.   Intermittent receiver audio:  Check for shorted terminals on the
     volume and squelch controls.

5.   Receiver sensitivity down:  Check for proper level of LR signal.  If
     down, check diode D-6 (1S2588) on the VCO Unit (X50-1370-10).

6.   Receiver audio jumping up and down:  Check C59 and C62 on RX unit.

7.   No receive or low sensitivity:  Check for proper output of 10.245MHz
     oscillator.  The 10. 245 MHz crystal may be defective.

8.   Intermittent receive:  Check discriminator colil L14 on RX Unit. It
     may be open.

9.   Meter lamp out:  Replace small lamp (B30-9996-05) as follows:

     1.  Remove meter
     2.  Remove wires
     3.  Remove small circuit board
     4.  Replace lamp
     5.  Reassemble