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.
Remove bottom cover, 4 screws.
From the Control unit X53-1180-xx unplug the rear mounted connectors 8-11.
Remove 6 screws from the board.
Swing the unit forward.
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.
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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