Kenwood TS-680S (TS 680 S TS680S) Squelch mods - adds squelch to all modes



Parts required
1 each 100 uF 20 v capacitor
1 each 10k ohm 5% 1/4W resistor
2 each 1N914 small signal diodes

Modification:

All modifications are to the signal board. Remove the signal board to gain access to the bottom of the board.

Remove R178 100 ohm resistor. (I cut the land between C177 and R178) (Removes FM chip control voltage) R178 is on the bottom of the board.

Add jumper with a diode in series between IC6 pin 14 and the base of Q57. Cathode of the diode goes to the base. (This is the squelch trigger control voltage) Q57 is on the bottom of the board.

Connect a diode between the 8V line (very near IC6) and pin 4 of IC6. This activates the FM chip (IC6) all of the time. Cathode goes to pin 4, anode to the 8 volt line.

Connect a 10 k ohm resistor between IC6 pin 4 and IC6 pin 14.

Connect a 100 uF 25 volt capacitor between IC6 pin 14 and ground.
(This slows this quick squelch down a little bit) Tests have shown (using commercial communications monitor) that activating FM chip IC6 does not degrade IF strip performance at all.