Some time ago I reported a (severe) problem with SSB modulation quality on
50 MHz of the TS-690S. There is now reason to believe that the cause of this
problem has been identified and thus the problem can be solved.
Thanks to Mike Gotch, G0IMG, it became clear that the bias voltage on pin 3
of the 50 MHz driver module (Mitsubishi M57735) is too low. This voltage is
8 V or less in the TS690, whereas the manufacturer specifies a voltage of 9 V
minimum. Mike also proposed a simple modification to increase this voltage to
the appropriate level (to be published in SIX NEWS of January).
I have forwarded this information to my dealer (Schaart in Katwijk, The
Netherlands). They did some thorough testing and came up with a similar
circuit as Mike, which can be implemented on the driver module PCB. The basic
schematics of the mod are given below.
Remove copper between 50T of CN3 and C7 on 10W final unit (X45-3420-00)
(this means that line 50T to Q1 of the driver PCB is NOT cut).
Add the following circuit.
------------ 14S of CN3 (13.8V)
| |R4 |
| | |
___ | |/
R1 |c R3 b | _______
___ b |/ |c | |
term. 50T of CN3 >---|___|----- | Q1 -------| IC1 |--> to p.3
_|_ | |_______| of module
| | |e | M57735
R2 | | | |
--- | |
| | |
R1 + R2 + Q1 = DTC114 or R1= 10k, R2= 10k, Q1= BC547 (NPN, Ic max= 100mA)
R3 = 3k3, R4 = 10k, Q2 = 2SA984 or BC327 (PNP, Ic max= 500mA)
IC1 = 7809 (1.5 A version in TO220 envelope)
IC1 can be located near CN1 with the metal side towards the cast alu. heatsink.
All other components can be located on the foil side of the PCB near CN3.
With this mod the known mod (STR nr. E51-92-038) of L20 on the IF board (100
uH -> 10 uH) is not necessary anymore.
In some cases the TS690 tends to oscillate. This is due to the critical
wiring in the filter unit. Especially the 2 blue wires of CN7 need to be
redirected away from the 50 MHz band filter. Even a ferrite bead might be
needed to prevent RF feedback. Also the grey thin coax from CN5 which is
folded near to the black relay K15 might cause RF feedback. The folded length
of coax must be redirected outside the filter compartment.
This modification has been published by my dealer, and will be forwarded it to
Kenwood Brussels. How long it takes to get acknowledged by Kenwood Japan is
If you are interested I can sent you a copy. Please send a SASE + 1 IRC or
SAE + 2 IRC's/1 US$ to me and you get the copy as soon as possible. If you
do not feel comfortable to implement this mod yourself, contact your local
If you or your dealer needs advice on the mod, please contact Schaart (tel.
+31.1718.15708, fax. +31.1718.73143).