The following change will reduce the tendency of the Zener diode in the Noise Blanker circuit to cause an increase in the ambient noise level. This change measures that no current flows thru this diode in the normal receive position.
560 ohm 1/½ watt resistor, (RD14CB2E561J)
On the IF unit (X48-1430-00) change R23 from 330 ohms to 560 ohms.
This change will be incorporated in all models beginning with serial number 603xxxx.
Time required for this modification is 1 hour or less.