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Kenwood TS-440SAT modulation problem

Discussion in 'Radio Circuits, Repair & Performance' started by K5RPM, Sep 9, 2011.

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  1. K5RPM

    K5RPM Ham Member

    Hey guys,
    I am a new ham and acquired a gently used Kenwood TS-440S with the built-in tuner (AT), plus an MC-60 desk mic with the pre-amp in it. The radio has recently developed a problem, specifically it has intermittent low modulation on SSB thru the mic. I say thru the mic because when I experience the issue I can immediately go to PSK31, which pipes in the audio from the computer to the ACC2 (13-pin Din) connector on the back of the radio, and have output power once more while the PSK is "squealing" away. I don't use the speech processor as I always get "great audio" reports during phone QSO's without the proc.

    I was hoping that maybe this is a known issue with the 440's. It will work just fine at times, and then at others I get no modulation....or should I say very little. I use my Kenwood TH-F6A (capable of Rx'ing HF) to monitor my phone transmissions and when the 440 isn't modulating I copy scratchy audio, like very low power signal coming out of the 440. I assume this 'hissy" reception is due to RF being picked up from the radio itself since I'm sitting in front of it while listening to the F6A. But when the 440 IS modulating it sounds like full-quieting into an FM repeater.

    Any thoughts before I start looking for someone who is savy at working on 440's? If you know of someone good in the Austin, Tx area please let me know.
    Thanks up front,
    Ron
    K5RPM
     
  2. WB2WIK

    WB2WIK Premium Subscriber

    Sounds like a microphone problem.

    Do you have another microphone to try?
     
  3. K5RPM

    K5RPM Ham Member

    I thought that too and unfortunately I don't have another Kenwood mic to fit the 8-pin plug. I'll try to borrow a hand mic or desk mic locally.
    ~Ron
     
  4. K5RPM

    K5RPM Ham Member

  5. K5RPM

    K5RPM Ham Member

    Well, I've always heard K-I-S-S.....Keep It Simple, Stupid. When i got home I opened up my MC-60's base and found one of the AA's out of its cradle, with the (+) button just resting on the tab that it's supposed to be pushed up against. Probably happened during shipping back in July and I just finally moved it around enough to where it was making intermittent contact. My Fluke DMM showed both AA's were at 1.22v too and were at the red/green line of my tester, which puts a small load on them. In went a new set...fully seated, and full modulation on several QSO's afterwards.
    To my defense, I wasn't aware of a powered pre-amp circuit until I read the article I found online. :D I'm still learning my radio.

    Ron
    K5RPM
     
  6. KA5IPF

    KA5IPF Subscriber

    Take the batteries out. The mic is powered by the radio, if you have a TS440.
     
  7. K9ASE

    K9ASE Ham Member

    Yahoo has a group for TS-440 owners with lots of good info too.
     
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