Kenwood TS-440S Has a Curious (to me) Problem

Discussion in 'General Technical Questions and Answers' started by K7QHU, Jul 13, 2019 at 9:28 PM.

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  1. K7QHU

    K7QHU Ham Member QRZ Page

    Hello,

    I have a Kenwood TS-440S that is presenting a curious problem. The radio receives great on all bands. The radio transmits great on all bands except for 20 meters. On 20 meters, if I try to transmit, the radio goes into transmit mode for about a second (red transmit light illuminates), then goes off. I thought it my be an SWR problem with the antenna, but checked the antenna with my antenna analyzer and it was okay (1.2 : 1). Just to make sure, I connected the radio to a dummy load and the same symptom occurs. I also noticed there was no output on the dummy load during the 1 second or so that the transmit light was illuminated (I was whistling into the microphone).

    I am hoping that someone in the group may have an idea as to what is going on.

    Thanks,
    Stephen
    K7QHU
     
  2. AA7QQ

    AA7QQ Ham Member QRZ Page

    Sounds like a low pass filter relay to me. Search for the service manual online & follow the RF path.
    Also, look up " ball point pen rf detector ". Build one & hook it to an ANALOG multimeter.

    Ed
     
  3. KK4NSF

    KK4NSF Ham Member QRZ Page

    Are you using the onboard tuner? or an external tuner?

    I've run into that before with my TS440s. In my case, it was a high SWR that the onboard tuner could not resolve.... and showed the same dummy load results that yours does. Rather than test by whistling, plug in a key and use that for tuning up...... then test with the onboard tuner set with the tuner on and off. Also try pressing the TUNE button, and let it do it's thing. You may also try a different antenna, if you have one.

    Also, you are not running an external tuner AND the onboard tuner at the same time, are you? (I've done that. It doesn't work well)

    one other idea.... if you are using your TS440s with a data cable, you may be getting RF feedback into the system. That ptoblem gave me all sorts of fits before Ifigured it out. Try disconnecting it. IF that turns out to be the problem, a few ferrites will go a long way toward fixing it.

    And if all the above fails.... see Ed's recommendation above.
     
  4. KA5IPF

    KA5IPF Ham Member QRZ Page

    Most likely: A shorted diode in the RX BPF on the RF Unit. Go to http://www.oz1bxm.dk/TS440/TS440S_Repair_FAQ.pdf and download the PDF, the RX BPF starts on abt pg 10 and has pictures for testing and repair. If the diodes check good check back and I have other ideas.
     
  5. K7QHU

    K7QHU Ham Member QRZ Page

    Thanks for all the suggestions. I will work on it this week as time allows and post my results.
    Stephen
    K7QHU
     

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