Modifications for the Kenwood TS-690

TS-690 50 MHz modulation problem solved

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   |
                                           | |     |
                                           ---     |e
                                      ___   |    |/
                                  ---|___|-------|  Q2
                      R1          |c  R3       b |        _______
                      ___     b |/                 |c     |       |
term. 50T of CN3 >---|___|----- |  Q1              -------| IC1   |--> to p.3
                           _|_  |                        |_______| of module
                           | |    |e                          |     M57735
                       R2  | |    |                           |
                           ---    |                           |
                            |     |                           |
                            ------------------------------------- GND

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 not clear...

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 dealer.
If you or your dealer needs advice on the mod, please contact Schaart (tel. +31.1718.15708, fax. +31.1718.73143).

Good luck and enjoy 50 Mhz with your improved TS690.

Enno J. Korma, PA0ERA
P.O. Box 6687
6503 GD Nijmegen, The Netherlands
General coverage transmisson modiication for the TS-450 and TS-690

  1. Remove all screws of top and bottom case.
  2. Remove two screws of front panel (left and right top side),and loosen two srews of front panel (left and right bottom side).
  3. Remove all screws of digital unit ( X46-312X-XX ).
  4. Cut the chip diode D27 (RL73) on digital unit rear side.
[      \                                              [
[   \__  __                                           [
[  \_ Bat. _                                          [
[   [      [                                           [
[    __\__                 \\\\\\               [
[              \\        [          [               [
[    [_\_[     [   [        [          [               [
[    [   [     [  [        [          [      ->I- D27 (RL73) CUT THIS
[    [   [     __ __        [\\\\\_      ->I- D26 
[    [\[                                    ->I- D25 [
[                                             ->I- D24 [
[                                             ->I- D23 [
[                                             ->I- D22 [
[                                             ->I- D21 [
[                                             ->I- D20 [
DIGITAL JNIT (X46-312X-XX)     Component side view
Best 73 Eric St-Pascal Kam. Qc. VE2MEL
Micro-input RFI modification TS450-TS690 Kenwood

By Pedro M.J. Wyns, RF- and biomedical-engineer.

After buying a ts690 I got considerable trouble with the vox circuitry.
The Vox gain was always too high due to an excessive feedback resistance in the vox amplfier. Apparently a PCB-mounting failure as the schematic carried the right value. After correcting this problem I still got RF problems with nearby antennas, blocking the transmitter in TX.

lack of decent RF-filtering on the micro-input circuitry.

adding ferromagnetic cores and adjusting rc-filters on the IF-board.

remove the connectors on the right hand side of the IF board (underside transceiver front towards you). Unscrew the board and fold over to the left. Add 22 nF parallel to R282 1k on t he micro entry close to Connector 6. Add 1nF parallel to C177 close to the IC-15 input. Add 1nF parall el to C217 close to the vox amplifier.
Remove te micro in and ground from the number 6 connector. Feed the white micro wire through a two hole ferrite core. Feed the inner conductor through a small ferrite core as well Reconnect...

If you might be using an MFJ (=major fucking junk) voice keyer, disconnect the shit-unshielded micro cable and replace by high quality twin balanced micro cable. Only use PTT, Mic and GND.

This concludes the mod. Don't even think of doing this without the service man ual and some smd-practice.

Good Luck

Pedro M.J. Wyns
Moutstraat 7
B-2220 Hallaar
Fax +32 15 303115
TS-690S 30KHz-60MHz RX

TS690 Mods. Mods for your Kenwood TS690 - by Tuomu OH1LEU Six News..........
In issue 36 of Six News there was an article concerning the Kenwood TS690. A few questions were asked. I hope the following information will answer a few questions, including the 30KHz-60MHz coverage. I have a 690 bought direct from the States and my friend Kari OH1MLD has one bought from Finland.
We have been comparing the differences between models! All band assignments are ontrolled by diodes in the digital unit, which is located behind the front panel. There are several (probably) yellow 4148 look-a-like diodes in a row, marked D20-D23. D23 affects the rx range. Removing it opens the receiver from 30KHz (yes!) to 60MHz continuously. Also any frequency change can now be controlled directly from the keyboard. D20 may have something to do with the WARC bands, at least in the US model there is only one diode D21, so you might like to try taking others away. Also the logic changes when entering a new frequency because of the "new bands", so be careful when you decide to operate!
If you want to make these mods, take both covers off, note the extra filters which are now the highest parts of the rig and note also that those little flat cables coming from the digital unit can very easily break. After that, loosen two lower screws (on both sides) that are securing the front panel and take away the two upper screws. Now the front part can be twisted downwards. Diode D23 can be removed easily from the digital unit PCB, located at the right hand side. You may also like to make some changes to the mic gain scaling. It is very easy to overdrive the PA. Between the mic gain pot an the centre tap is a 10k resistor which causes the mic gain to be somewhat non-linear pot, but, if for example I had the mic gain at 9 o'clock now I can turn it to nearly 12 or even more. This is very handy when using the processor, the ALC setting is now not as critical.
The maximum gain remains the same. You may have noted that the AM band has poor sensitivity. You may change the coupling in the RF-unit on that particular band 500KHz-1.6MHz. The coupling has two 39 ohm resistors (R6, R7) in series, controlled through a 10 ohm resistor (R8) between them. Changing the 10 ohms to a miniature coil 1uH and those 39 ohms to 0 ohms makes AM sensitivity much better. If you live near an AM station forget this mod! The SMD components are located in the RF-unit, from the CN4 connector and IC2 towards the centre of the PCB, at the opposite end to the filters. I would recommend the ourchase of a service manual before undertaking these mods. I can also not be held responsible for any damage Hi! 73 de Tuomo OH1LEU.

Note Cutting D23 reverts the 690 back to Japanese spec i.e. full Rx coverage up to 60MHz but only 50w o/p on 10m due to their regulations.
(Thanks G0HVQ)

There it is. I don't take any responsibility for any damages on your radio, or violation of any regulations. Perform the mods at your own risk. I haven't tested this myself. If you have any questions, I can't help you, I'm just relaying it off the internet. 73 de Andreas, LA8AJA.

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