Discussion in 'Radio Circuits, Repair & Performance' started by ZL1AY, Nov 20, 2021.

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  1. ZL1AY

    ZL1AY Ham Member QRZ Page

    My TS120s transmits full power with PTT (ssb) and Send (CW), and odly when the Key is inserted the audio tone starts.
    The key is open circuit, tried a blank phone plug same result?
    The RF gain controls the output power not the Carrier!, the power signal is a clean sine on Send CW and ssb continuous.
    Please advise
  2. W1GCI

    W1GCI Ham Member QRZ Page

    According to the manual, the TS-120 requires a three-pole key jack - like a stereo headphone jack. Using the standard 2-pole jack used for older transmitters will short out when inserted give a constant key-down condition. Gets me more times than I'd like to admit.
  3. HB9PJT

    HB9PJT Ham Member QRZ Page

    I suspect that the CW key is not working correctly to send a CW transmission when the sound is there as soon as the key is plugged in. Probably the TRX is not ok. Have you tested the output power with a power meter when transmitting with your CW key?

    A 2-pole key connector seems correct.

    73, Peter - HB9PJT

    Last edited: Nov 20, 2021
  4. W9GB

    W9GB Ham Member QRZ Page

    As noted in the Operation Manual, the Key Jack has +9 Volts on Center Conductor.
    Shielded cable and Polarity MUST be maintained to Key.
    The Manual notes an Electronic Key, versus a Straight Key.

    Page 10 (picture)

    KEY JACK, part number E11-0005-15
    1/4” (0.25 inch), 3-pole Phone Jack (TRS)
    Use a TRS (Tip-Ring-Sleeve) 3-conductor Phone Plug (a.k.a Stereo plug) with a shielded cable.
    Last edited: Nov 20, 2021
  5. ZL1AY

    ZL1AY Ham Member QRZ Page

    Thanks guys
    Yes the CW power output is a clean sine wave into 50 Ohm 1Kw dummy load and scoped.
    Weird that the "RF gain" controls the output power, instead of "Car" control.
    Ok with the phone jack, used to work for years, now it does not , but tried stereo plug.
    Might have to to see inside the area of the finals enclosure, maybe a short somewhere.
    This is a nice old rig would like to see it go again, we had a ZL that used to service them but is now silent key.
    Will gather more symptoms data over time and post them here in more detail.
    Many thanks.
  6. ZL1AY

    ZL1AY Ham Member QRZ Page

    Problem found, on inspecting the internal rear panel assembly, the 3 pole phone jack had desintegrated shorting out a black wire.
    Not to sure what damage this has done but need to locate genuine part now.
  7. W9GB

    W9GB Ham Member QRZ Page

    I checked East Coast Transistor (Kenwood Parts, Eastern USA)
    Discontinued, last sold for $ 5.88 USD.
    MEASURE and Understand Configuration of Kenwood OEM Jack.
    Many non-USA manufacturers (East Asia) actually design as Metric,
    BUT the Phone Jack is greater than 100 years old (Manual Telephone switchboard usage).

    Switchcraft has been Phone Jack (0.25 inch) standard for decades.
    Switchcraft, Inc. was established in 1946 to manufacture jacks, plugs, and switches,
    mainly for the communications industry.

    There a Numerous versions, some with additional switching when plug is IN or OUT,
    as well a Solder Lug and PC mount terminals and Panel thickness sizing.

    This is the Switchcraft 112BX model (photo below).
    Switchcraft 267 - 3-conductor Plug (0.25 inch)
    Last edited: Nov 21, 2021
  8. ZL1AY

    ZL1AY Ham Member QRZ Page

    Ok thanks for the info, after examinating the broken phone jack socket I will hardwire the Key until I can find the right socket.
    PTT still gives full power on SSB, Send CW gives full power too.
    Back to school.
  9. VE7DQ

    VE7DQ Ham Member QRZ Page

    You might search through the Kenwood TS-120S service bulletins. There are one or two that may apply to this oscillation problem.

    A quick first step would be to snug down the 6 screws holding the RF board (the board with the bandswitch) and the relay board attached to the low pass filter cage. Ensure that the coax connector is reeealllly tight.

    There are a couple of diodes on the RF board that can short out and cause that uncontrolled full carrier operation. Seeing as to how the RF gain control affects output, my guess is that one of those diodes has shorted. See service bulletin 832R

    The RF board can be serviced from below without removal from the chassis by unscrewing the IF board on the bottom of the radio, moving it carefully out of the way, and then removing the plate underneath the IF board. It's fiddly, but doable.
  10. ZL1AY

    ZL1AY Ham Member QRZ Page

    Worth checking out.
    Have tightened screws on the boards and antenae socket.

    There quite a few diodes on rf board, have to identify which ones.
    Checking Service bulletin 832R

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