RX340 First Mixer BITE Failure


Symptom:  RX340 fails BITE
          BITE 1:  FAIL
          BITE 2:  FAIL  S/A MIXER 1
          BITE 3:  000:036 or 000:004

This failure indicates that the first mixer is out of balance.  In most cases, this does not cause any noticeable problems in operation.

The cure is to adjust the first mixer balance.

Procedure:  Warm receiver up for at least one hour
            Disconnect antenna
            Set MODE to CW 1
            Tune RX340 to 0 Hz
            Adjust R5 and C11 on Mixer 1 board for minimum S-meter reading

R5 is inside the rectangular shield can at the end of the board closest to the front panel.  C11 is just behind the shield can.

NOTE:  These adjustments are VERY touchy.  It helps to replace C11 with a multiturn piston capacitor and R5 with a multiturn potentiometer.  C11 is 1-6 pF and R5 is 1k.  I used a Tekelec Temex 0.8-6 pF ceramic piston trimmer and a Bourns PV37W102C01B00 1k, 12-turn 6mm sealed cermet trimmer (Mouser 81-PV37W102C01B00, Digi-Key 490-2969-ND).  I soldered the body leads of the piston trimmer to the shield can, and its other lead to the PC card, for a very sturdy installation.  The pot's wiper lead needs to be bent to fit the PC card, but it is a clean and sturdy installation.  The pot is still pretty touchy -- perhaps a 500 ohm pot and two, 250-ohm resistors, or a 200 ohm pot and two, 400-ohm resistors would be better.  Or maybe just a 10k pot.