TS-480HX SSB TX Low power problem

Discussion in 'General Technical Questions and Answers' started by VA7WPN, Jul 2, 2020.

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  1. VA7WPN

    VA7WPN Ham Member QRZ Page

    I have a problem child of a TS-480HX, on SSB when I key up the microphone and talk. What I have found is that if I key up and make a loud noise or click the power output will increase. If I don't, it's almost like there is only a few (20-500) mw. It does this on SSB, I have not tried it in AM or FM yet. But when I do CW it's been mediate full power.

    My rig is an HX. And after looking at the service manual, I am leaning on Q625, the initial op amp in the audio input stage on the TX/RX board. Its as if it's not turning fully on, low sense voltage? Until a loud noise is made.. spiking the input and turning on.

    As CW doesn't use this stage, it's not affected. Helping me narrow down the possible cause and location.

    Does this make sense to you?

    John Brent
    VA7WPN
     
  2. W1VT

    W1VT Ham Member QRZ Page

    What are you using for a PEP reading wattmeter on SSB?

    Zak W1VT
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    There should be no output power at all on SSB when you just press the PTT, if you don't modulate the rig by speaking into the microphone.

    This mode was originally called SSBSC (single sideband suppressed carrier) and ideally the output when not speaking should be absolutely zero.
     
    WB5YUZ likes this.
  4. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Have you tried a different mike yet?
     
  5. VA7WPN

    VA7WPN Ham Member QRZ Page

    I understand that, but there is no carrier when I am talking into the mic, until I make a very large noise that "Trips" something making it ramp up the power.

    I have tried a different mic, but I will try an other one just to be sure.
     
  6. KM3F

    KM3F Ham Member QRZ Page

    Sounds like VOX is turned on and set too high to trip on..
     
  7. VA7WPN

    VA7WPN Ham Member QRZ Page

    I did two.. full.. resets. But.. I will check to see if that is an issue. Thank you, not one I thought of.
     
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    See Steve's post #3 again. There is not supposed to be a carrier in SSB. If you are seeing a "carrier" after you make your loud noise, you may be seeing oscillation somewhere in the audio or rf chains, which would point in a very different direction as far as troubleshooting is concerned. But I don't think that's what you mean.

    Did you perhaps mean, "There is no significant output when I am talking into the mic until I make noise, etc."? That makes a little more sense.
     
  9. VA7WPN

    VA7WPN Ham Member QRZ Page

    Exactly what I mean, I have done some digging into the radio. I found that there was a leaking cap, it had been MARS modded, and there was a cap bridging an other component in the bottom side of the radio. I fixed thos problems, as well as touched up some component leads (Antenna connections) along with reseating ALL interconnection cables and ribbons.

    The radio seemed to work perfect after that. But only a day or so later, it started acting up again. I have a feeling its in the amp stage, and is a temperature related fault. But.. I have been wrong EVERY TIME so far, so Im probably going to chase this for a while.

    I am seeing the following :
    -TX / RX LED is changing from green to red appropriatly
    -I clearly hear my voice, and CW / FSK tones when I have TX Monit turned on (Even when there is no TX output)
    -RX AF is always very nice, its clear and bright.
    -Both fans come on when radio temp increases
    -Voltage drop is minimal. Stays between 13.2-13.8v on two 40a Power Supplies
    -Power Output (When properly functioning) is within service manual specs on all bands and all modes
     
  10. WA4ILH

    WA4ILH Subscriber QRZ Page

    Bridging a component with a cap was not part of any "MARS MOD" that I know of.
    Tom WA4ILH (formerly NNN0BVA)
     

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