Modifications for the Kenwood TR-7800

TR-7800 Loss of Memory


Intermittent loss of memory may be corrected by adding one resistor at the microprocessor on the control unit.

  1. Remove bottom cover, 4 screws.
  2. From the Control unit X53-1180-xx unplug the rear mounted connectors 8-11.
  3. Remove 6 screws from the board.
  4. Swing the unit forward.
  5. Install a 470K ohm 1/8 watt or larger resistor from connector 11, "UP" pin, to ground. (microprocessor pin 35, PA2 port). Space is limited: Be certain not to create a solder bridge when installing the resistor.
  6. Reverse steps 4-1 for reassembly.

TR-7800/TR-9000 Optional Ceramic Filters


FM Adjacent channel rejection in either unit may be improved by installing an optional narrow ceramic filter.
Filter    Part No.       -6db Bandwidth -70db Bandwidth Retail
CFK-455F  L72-0304-05    +/- 6 kHz      +/- 12 kHz     $ 33.50
CFK-455G  (CFK-455G)*    +/- 4 kHz      +/- 10 kHz     $ 33.50
* Not original part. No computer part number.

TR-7800, RX unit X55-1270-10 part, L10
TR-9000, RX unit X55-1260-11 part, CF1
To install, desolder the original filter and clear the second set of holes for the optional filter. Solder the new filter in place. Be sure all pins are actually soldered, and that there are no solder bridges between pins or across the printed circuit board. Clip the pins flush to the board, and reinstall the circuit board.

Note: Squelch operation will vary from unit to unit with an optional narrow filter. Tighter coupling from the detector to the squelch circuit may be tried to restore "original feel".

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