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World of Ham Radio 1997
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==============================================================================
K E N W O O D
>>> A M A T E U R R A D I O S E R V I C E B U L L E T I N <<<
==============================================================================
Kenwood Service Centers
Kenwood Service Corporation Kenwood Service Center, East
2201 East Dominguez Street 829 Lynnhaven Parkway, Suite 130
Long Beach, California 90801 Virginia Beach, Virginia 23452
Telephone 1-310-639-5300 Telephone 1-804-340-1702
==============================================================================
BULLETIN # 918
MODEL: TS-940S
SUBJECT: SQUELCH SWITCHING NOISE
In some TS-940S below S/N 711xxxx, a "popping" or "clicking" noise may be
heard when the squelch circuit is opened or closed. This may be more
noticeable when an optional CW filter is installed. The following procedure
will minimize the noise.
Parts required
R194 560K ohms 1/6W RD14CB2C564J
R197 220 ohms 1/6W RD14BB2C221J
R355,356 220K ohms 1/6W RD14BB2C224J
C284 0.47 uF, 50V electrolytic C90-0484-05
Procedure:
1. Disconnect the power cord and antenna from the transceiver.
2. Remove the top and bottom covers (16 screws).
3. Locate the I.F. board on the bottom of the transceiver.
4. Remove the 7 screws from the I.F. board.
5. Carefully unplug connector # 17 (right side of optional CW filter)
by prying up on the plug. Do not pull on the wires.
6. Move the 4 wires (yel, org, brn, red) that run across the far side
of the I.F. unit out of the way so the board may be removed.
7. Carefully lift and rotate the board toward the left side of the
transceiver to expose the foil side of the board.
8. Using a small craft knife, cut the foil at the 3 points shown in
figure 1 (top right corner of the board).
9. Unsolder and discard resistors R194 and R197. They are mounted on the
component side of the board and soldered on the foil side.
10. Install a 560K ohm resistor on the component side of the board
as shown in figure 2. This resistor is now designated as R194
11. On the foil side of the board, add the 3 resistors (R197,355,356)
as shown in figure 3.
12. Add a small jumper wire as shown in figure 3.
13. Add capacitor C282 as shown in figure 3. Observe polarity and
insulate the positive (+) lead with shrink tubing.
14. Carefully place the board in its original position (do not pinch wires)
and secure it with the 7 screws.
15. Plug in connector # 17. Move the 4 wires on the far side of the
board back to their original position.
16. Put the covers back on the TS-940S and secure them with the 16
case screws.
17. Connect the antenna and power cord then test the transceiver for
normal operation.
This is an optional change that may not be performed under warranty.
Time required for this modification is 1.0 hrs or less.