Modifications for the Kenwood TS-700

9600 and TS-700a

1st March 1991

I connected the 9600 baud input directly across R21 (33 kilohm) on the Generator Unit Board via a 10 microfarad tantalum capacitor.
The + of the tantalum is connected to the junction of C23,R21 and R22.
The - of the tantalum goes to the conductor of the shielded cable, and the earth shield to the immediately adjacent earth terminal.
I carefully scraped off the 'insulation' on the top of R21 (approx 5mm) and soldered the + of the tantalum to it.
The 10 microfarads was basically for isolation. I originally intended to match the load as per James Millers article by modifying C34, however I just adjusted VR1 and because it works like a charm I have never bothered to attempt matching.
I have also been meaning to run the JAS-1 via the varactor for Fuji-Oscar 20, but once again have not got around to it. With the launch of all the Digital Satellites, time just seems to fly, especially when we have daylight saving, as the first evening pass goes by between 11pm and 12 midnight. Just lately I have been going to bed at a respectable hour, hence the dealy in answering.
However this weekend Daylight Saving finishes, so UO_14 and AO_16 will be here 'an hour earlier', which will be just great.

Service notes on TS-700A

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 20 (18-10-1977)

Power supply

  1. 9 volts down: The MFC4060 Q11 and 2SA495 Q9 are bad.
  2. No 21V: Replace Q3 (2SC733Y (X43=1120-00) Power Supply Unit.
  3. Dial light is VERY bright: Replace shorted Q2 2SA671 on rear panel.
  4. Intermittant +9 volt supply: The legs of Q12 2SD235 are too short at the PC board. The leads were pulled away from the board. Replace Q12.
  5. Power supply intermittant when tapped: Check for short leads on pass transistors, pulled out of circuit board.
  6. No RX - No TX: Check diode D6 Zener in power supply. -6V supply. If shorted, replace.
  7. No 13.8 volts at power supply: The wire on bridge D1 is not soldered.
  8. +9 volts is okay, but 21 volt onl 16 volts: Q1 is bad in the power supply 2SC733Y.
  1. No modulation: Replace bad diode D15 Varactor on X52-1080-21.
  2. USB or LSB is too high frequency: Recheck alignment of carrier board according to TKC service Manual procedures.
  3. No RF out AM CW SSB: Replace D13 on GEN unit X52-108021.
  4. FM RX and TX different frequency: Readjust all HET unit frequencies. Also check VFO linearity and adjust TX frequenc L3.
  5. TX wrong frequency: Adjust L3 at X52-1080-21. 10.7 oscillator for final TX frequency.
  6. No power out FM: Check for loose connection at L3, the 10.7 coil on GEN unit X52-1080-21.
  7. No TX or RX: The fixed channel switch is in the wrong position.
  8. Low poer out only 8W. 21 volt supply down to 16V: The protection diode D7 in the power supply is shorted.
  9. VFO drift: Q1 3SK22Y in VFO is bad.
  10. No TX FM: D15 on X52-1080-21 GEN is bad.
  11. Drive control does not peak: This is normal - leave at center 500 position.
  12. No TX: TX B terminal touch to ground at X52-1080-21 GEN unit.
  13. No TX FM: Check diode D16 on GEN unit.
  14. Only 3 watts out: Bad Q2 2N5642 in final amplifier.
  15. The RF meter doesn't Work, but TX output okay: Bad diode D1 on BPF, the 1N60 is open.
  16. No TX: Bad Q3 in mixer unit (X48-1130-21) 3SK35 (BL).
  17. No VFO output: Cold solder joint of R2, 100 ohm resistor inside VFO on circuit board.
  18. Intermittant TX: Bad ALC pot on mixer board VR2 (X48-1130-21)
  19. No TX 147 Simplex: Loose resistor not soldered on rear circuit board of band switch.
  1. Spurrious signals on receive; if the output level or VFO is too high or mixer Q3 on HET unit: SN76514 is bad.
  2. IF the noise blanker does not work: Check Q6 2SK19GR on X55-1120-00.
  3. There is no audio from receiver-no 21 volts: Q1 2SC733(Y) in 21 volt supply is bad.
  4. FM receiver sensitivity is down 30 - 40 db: Check 10.245 xtal at TP-1 on FM IF unit. If oscillator level is down, replace crystal.
  5. Receiver sensitivity is intermittant and TX intermittant: Check contacts RT relay. Replace if bent or miss-contact.
  6. If you cannot adjust the center meter: Maker sure Smeter start, VR4 is set at zero. If you cannot get enough adjustment with center meter, adjust VR1, replace Q4 (2SK19GR) on X55-1120-00.
  7. No receive: Check for solder touch at 133 terminal on Het unit, if ther is no 133 het output.
  8. No RX or TX and no VFO light: Check diode D2, 1N60 located on VFO circuit board.
  9. VFO drifts or moves wit shock: Wire is not soldered VFO main coil L1.
  10. No repeater operation: Check for wire that is touching at repeater switch.
  11. No receive: Resistor R7 is touching Q1, 3SK41 on X55-1120-00 board.
  12. No RX on 144, or any single band: Check HET xtals-realign the Het unit.
  13. Center meter drifts for the 300000series and before: Send for the TKC bullent on Center Meter Drift.
  14. VFO is intermittant when turned: There is loose tension on VFO rotor and Stator plate contact. Rebend tension spring.
  15. RX audio output distorted: Chec Q4 on X49-1060-00.
  16. No SSB or CW receive: Resistor R73 is touching to the can of T6 on X52-1080-21.
  17. FM receive okay but SSB sensitivity is down: Check alignment of SSB IF transformers T4,5,6.
  18. FM receive is bad: Bad T1 on the X48-1140-20.
  19. Scratchy audio with internal speaker: Check for bad speaker.
  20. No 146 band: Replace bad Het Xtal on Het Board.

TS-700A for Repeater operation in Europe

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 5 (June 11 1975)

We have had serveral inquirics about repeater operation of the TS-700A in Europe. The 2 Meter abnd in Europe is 144 MHz to 146 MHz with repeater operation in the 145 MHz to 146 MHz range. The repeater offset is generally 600 KHz down from the output frequency. The repeater offset in the TS-700A occurs only in the 146 MHz and 147 MHz bands. By changing these to 144 MHz and 145 MHz, respectively, and changing the appropriate offset, the TS-700A can be used with European repeaters.

The TS-700A uses varicap diodes to tune the HET unit, MIX unit and RX NB unit because of the 4 MHz coverage. These varicap diodes are used to resonate various stages, precluding the need to retune from band range to band range. The varicap diodes are biased by resistors that are selected by the Band and REPEATER switches. These bias resistors must be changed if the band frequency and/or offset crystals are changed. The table below shows the resistors and crystals that need to be changed to make the TS-700A useable with European repeaters. All resistors are 1/4 watt.


Part No.145-147 MHz144-145 MHz
X3127.100 MHz125.100 MHz
X4128.100 MHz126.100 MHz
X6128.700 MHz125.500 MHz
R3162 K39 K
R3282 K47 K
R34100 K39 K


Part No.146-147 MHz144-145 MHz
R10312 K22 K
R1048.2 K15 K
R11012 K15 K
R1126.8 KDelete
R1136.8 K18 K
ADD138 K

It is necessary to remove the front panel to make this modification.
To do this, remove the top and bottom cabinet halves. Next, remove the FINAL tuning shaft by loosening the chaft coupling and pulling the knob and shaft out. Then, remove the six screws (3 on each side) holding the front panel. Remove the BAND and DRIVE knobs and the nuts holding these controls. Gently pull the front panel out until there is anought room to work on the BAND SWITCH unit.
The 138 K resistor that is to e added consists of a 120 K resistor and a 18 K resistor in series. It is connected from pin 3 of the band switch to ground. Show below is a diagram of the BAND SWITCH unit.

After installing the new resistors in the BAND SWITCH unit, reassemble the front panel, leaving out the FINAL tuning shaft. The procedure for replacing the resistors in the HET unit is to first remove the three screws holding the board and tilt it up towards the VFO. Plugs P-1 and P-2 may be removed if necessary. The resistots that need to be changed are located on the outside edge of the board. Replace the resistors and reinstall the board and connectore. Install the crystals in the sppropriate sockets (X3, X4, and X6). Replace the FINAL tuning shaft and align as per page 40 of the Service Manual.
Replacement of 9V regulator IC MFC.4060 with improved MC1723CL-A

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 27 (28-12-1977)

X43-1250-00 PCB comes complete with mounting hardware and extended leaded leads for easy installation. Procedure:

  1. Remove old IC MCF4060-A Q11.
  2. Remove R27 1.5Kohm (Delete). Replace with wire jumper.
  3. remove and reinstall R28 1Kohm on foil side of PCB.
  4. Mount PCB per illustrations (observe lead call-outs between X43-1250-00, new PCB, and old Q11 position (X43-1120-00).
  5. Reset VR1 for 9.0V measured at power supply output terminal.
  6. Reset VR2 for 21.0V measured at power supply output terminal.

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