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Kenwood TS-440SAT low power, swr meter pegged!

Discussion in 'Radio Circuits, Repair & Performance' started by W1MM, Jun 13, 2018.

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  1. W1MM

    W1MM XML Subscriber QRZ Page

    Actually, J3-2&3 should be at the same DC potential as they just loop through the Final. The signal originates from Controller board A2, J10-5 which traces back to IC1, pin 45. In my service manual that is marked 0V which is essentially what I have. So, unless that DC signal is supposed to change on TX, this is another dead end.

    Also noteworthy, if I do nothing else other than extract the pin for the blue wire from J2-2 which is the -5V power buss, with everything else connected, I get full power from the rig. But, the SWR meter is still pegged.
    Last edited: Jun 22, 2018
  2. KA5IPF

    KA5IPF Ham Member QRZ Page

    The signal originates on the Filter unit. It should be zero. Your VSR should be zero also, that's what is killing the tx power by turning down the ALC. I will bow out as you know more than I do.
  3. W1MM

    W1MM XML Subscriber QRZ Page

    Well, a second set of eyes on it is always better. I appreciate you looking at it.

    I would also have to disagree about where the signal on J3-2&3 originates. If the block diagram is to be trusted, that signal originates from the controller board to trigger the SWR circuit. The output of that ends up at the Q46 ALC input on the IF board J19-8! I'm having a tough time believing it should be 0V at all times, even during TX. I'm almost leaning in the direction of a microprocessor glitch that may need a full reset.

    Another thing I plan to look at before resetting the MPU is the voltage at J4-4 when I pull the -6V from the filter board.
  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    I would suggest to listen very closely to Cliff. He is the resident K-wood repair guru. I think you will find no more K-wood knowledge, unless you were at the factory.

  5. W1MM

    W1MM XML Subscriber QRZ Page

    With all due respect to you and your "resident guru", I can read a schematic diagram. On a TS-440, VSF & VSR cannot be 0V under any condition if the +5V regulator is working correctly, which it is. It certainly is unconventional and may not apply across all Kenwood models. I don't know because I'm not familiar with other Kenwood models. But if he takes offense to my contradiction and cannot have a mature discussion about it, so be it.

    I will put out the call again. If anyone out there has a working TS-440, would you be kind enough to take some voltage measurements for me from the attached spreadsheet? Even if it's just the PCB connectors which are easily accessible. It would be greatly appreciated.

    Attached Files:

    Last edited: Jun 22, 2018
  6. AA7QQ

    AA7QQ Ham Member QRZ Page

    Mine is all apart, as I was going to use the PA/LPFs & BPFs for an SDR project. If I get the time this weekend, I will look over my enlargened schematics.
    I doubt that I can give any readings, but will look it over.

    You really should reconsider about Cliff. He has helped hundreds, if not up to a thousand people on the forums. He knows these radios inside & out. You can decide not to, but in the end, you will most likely see that the old Man was right.

  7. W1MM

    W1MM XML Subscriber QRZ Page

    Well, I took a shot and missed. Bought a working pull TX Filter board off ebay, dropped it in and got exactly the same result. {sigh}
    So, the trouble is someplace else in the feedback loop. Perhaps on the IF board or even (God forbid) the control unit.
  8. CX3CP

    CX3CP Ham Member QRZ Page

    perhaps also something related to the ALC.
  9. W1MM

    W1MM XML Subscriber QRZ Page

    That was my thinking too, which is on the IF board. Only part that would not make sense about that is the pegged swr meter indication. Before I get too crazy, I think I'm going to go back and look at simple things again like the coax jumper between the TX filter and the AT. I used that same jumper to attach my 50 ohm load to the TX filter output. I really dislike the tight bend they put in it at the AT side.
  10. AA7QQ

    AA7QQ Ham Member QRZ Page

    How about bypassing the whole ATU unit? THey do fail.


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