Modifications for the Kenwood TS-140
TS-140S Sidetone Mod
I recently purchased a Kenwood TS-140S after using it on CW for
about a week, I decided to try it on SSB and AM. When I pushed the
AM and SSB mode switches, I heard a constant audio tone emanating
from the rig. As I diconnected the rig, preparing to return it
to the factory, the tone stopped.
Investigating the circuit diagram, I noted that the CW key has
to be unplugged to kill the sidetone. There is no mention of this
in the Instruction Manual.
Perhaps my experience may save others the frustration I encountered.
Also, amateurs should pay attention to the proper use of receiver
noise blankers. I know of instances where operators were handing
out reports of distorted signals to outhers, only to discover that
it was their improper use of the receiver noise blanker that was
producing the distortion...
TS-140S Intermittent loss of TX power
In some TS-140S transceivers, the drive transistor, Q2, is not firmly
mounted to the heatsink. This can cause a loss of transmit power after the
unit warms up. The following modification will correct this condition.
This modification may be performed under warranty.
Disconnect the TS-140S from the antenna and power supply.
Remove the top and bottom covers. Open the sub-chassis. Refer to the
instruction manual for step by step instructions.
Remove the shield plate from the sub-chassis (12 screws) to expose the
filter an final units. Do not loose the 2 springs that are secured by the
right side screws.
Resolder Q2 so that the transistor makes firm contact with the heat
sink on the Final unit. Tighten the transistor's mounting screw.
Assemble the transceiver by reversing steps 1 through 3.
Time required for this change is 1/2 hour or less.
Broadcast Sensitivity Modification for the TS680S / 140S
Between .500 and 1.6 MHz attenuation is added to reduce? front-end
overload on the Broadcast band. Some of us BCB DXers find this a
HIGHLY undesirable feature. If I want attenuation I will use the
front panel switch. The following mod will restore the sensitivity -
Cut the land between IC1 pin 11 and R7 (SIGNAL UNIT, M54581P)
Cut the trace between IC1 pin 12 and R10
Add a small signal diode (1N914, 1N4148) between IC1 pin 11 and R7
(Cathode towards R7)
Add a small signal diode between IC1 pin 12 and R7 (Cathode towards
Trace the lands from pin 11 and 12 of IC1 and you will find a good
place (to the left of connector CN5) to cut these traces as well as
pad to solder the diodes to.
TS-140S TX All Freq Mod
To enable the TS-140S for transmitting on all bands:
Disclaimer: This Modification is for those who need it to operate MARS only.
Disconnect radio from power supply and antenna
Remove top and Bottom covers
Locate the control board (I believe it is on the bottom --NOT BEHIND TH
THE KNOBS LIKE THE 440!!)
Cut D31 on the control board
Reassemble the radio
Reset the radio by holding the A=B switch while powering up the rig.
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