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Thread: TH-28A: random beeping, like a stuck key, but no key seems to be stuck.

  1. #1
    travis.farmer's Avatar
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    Default TH-28A: random beeping, like a stuck key, but no key seems to be stuck.

    ok, this is very odd. my TH-28A seems to beep randomly. like if it was on key-lock, and a button randomly made contact. though it is not on lock, and the radio does not act as though a button is making contact. i checked all the buttons, to see if they functioned correctly, with the exception of the PTT, and everything seems to respond as it should. it is not the PTT button, and the on-air light does not light (fortunately, that would not be a good thing, to randomly TX).
    has anybody encountered this issue, or a similar one?

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  2. #2
    Super Moderator 5B4AJB's Avatar
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    Have you done a reset? it usually involves holding a few buttons down and powering on.

    It might be the internal battery need replacing too...

  3. #3

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    I have seen a key edge get caught under the case edge next to a button, but not on a radio. You might check for that.
    --
    73, Jim/N4AAB got my Extra class license on Aug 10, 2017. Vanity call in Oct, 2014.
    My Ham radio site has no popups, no music, no banners.
    'Through the thorns to the stars' from Ghost-in-the-Shell anime.

  4. #4
    travis.farmer's Avatar
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    the reset seems to have done it
    the internal battery tested good.
    the buttons all look good, none stuck.

    seems to be good now, thanks!

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  5. #5
    travis.farmer's Avatar
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    ...and the beeping continues. i guess the reset only put it off for just a bit.
    the internal voltage was fine, and it still retains memory after a main battery removal.
    perhaps it is just an artifact from age, or the previous owner may have dropped it, got it wet, or something.

    I just won't be able to use it for digital communications. perhaps in the future, it may work as a FOX radio. providing i turn the sound down

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  6. #6

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    Pull it to pieces, and investigate! You might discover a tiny bit of grit or broken membrane which with your tec licence, should be able to fix. A bit like qualifying as a car mechanic and then giving your car to the dealer to investigate a rattle!

  7. #7
    travis.farmer's Avatar
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    Sorry for the late response, i have been busy pouring through the service manual for the radio. and thanks for the kick to pull apart the radio. due to a variety of mental issues (Asperger's, A.D.D, etc...) i sometimes need a kick to get me to look in the obvious places.

    this radio seems to have a few more issues than i personally do. intermittent speaker output with the squelch completely open, lack of transmit (into a quick made dummy load), or at least the "On-Air" LED didn't light, and the beeping. i will pull it apart this weekend and do some tracing with my scope to find out where the audio stops.
    i may temporarily bypass the speaker and mic jacks to see what that solves. both seem to have intermittent contact between the terminals, and the shunts.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  8. #8
    travis.farmer's Avatar
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    well, i have been up one side of this radio, and down the other. still no RX audio, no TX into a meter with a dummy load, and not even any signal strength shown. i am starting to think the only thing that works on this radio is the microprocessor, LCD screen, and the back-light. I have done resets, and checked the memory battery (good). the only thing i have not tried is if it has any results with an external mic/speaker. i only ordered that as at the time, some stuff worked.
    i think i just simply got taken by a bad purchase, and a series of accessories, all based on good intentions that i had a good radio.

    I suppose i at least have my HF rig...

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  9. #9

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    About the only thing left I can think of is the keypad itself. The little metal buttons inside, its typically all one piece, are bulges that spring back up after they are pressed and released. My remove control does that. I can press and press on a number, and nothing happens. Then I suddenly get multiple of the same number. Its a known problem with this type/model of remote.

    So it could be the opposite, instead of failing to be seen as being pressed, your radio has a button that is seen as always pressed.

    I would guess ghe keypad would need to be replaced, unless each button is separate inside the radio. Then just the one not working.
    --
    73, Jim/N4AAB got my Extra class license on Aug 10, 2017. Vanity call in Oct, 2014.
    My Ham radio site has no popups, no music, no banners.
    'Through the thorns to the stars' from Ghost-in-the-Shell anime.

  10. #10
    travis.farmer's Avatar
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    I tested the function of all the buttons. none miss presses, and none hold presses. though the PTT (with dummy load), is problematic. it only blanks out the busy indicator for a moment, and the "On-Air" LED never comes on. could be a gremlin in that particular circuit/button.

    i am awaiting a 2.5mm to 3.5mm plug adapter, as i have none on hand. then i can construct a test fixture to test the external speaker/mic jacks by simulating stimuli, and probing around with a scope.

    the email i sent to Kenwood was almost fruitless, as they no longer support/repair this model. though they did send a slightly better schematic PDF, so it wasn't all bad.

    while digesting the schematic, it occurred to me that the AF amp may not be bad. i probed with the scope at the volume pot, and that is before the AF amp. kinda leads me to believe that something is blocking the audio entirely. i am reminded of the first time i pulled it apart. the lead from the antenna BNC core to the PCB was bent in various directions. i should check around the PCB connection for cracked solder, and/or PCB traces. i know not what bent the lead, but whatever it was could have stressed the connection. it would explain the lack of signal meter on the display, and the lack of AF, as well as the lack of RF out on a meter.

    I don't have the time at the moment to confirm or deny any of this right now, but it gives me someplace to start looking, and it has given me renewed interest in solving this very perplexing issue. i may even wake up early and take a look at it before work.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  11. #11
    travis.farmer's Avatar
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    I looked over the antenna PCB solder joint very carefully under a magnifying light, and found no cracks in the solder or PCB, and no cold solder joints.

    interesting new development: HOT batteries, while the radio was OFF!
    I removed the batteries for now, as i will look into this after work.

    anybody here qualified to perform an exorcism on radios?

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  12. #12
    travis.farmer's Avatar
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    something that occurred to me. if the RF power amp module got cooked, would it cancel out the RX as well? i can get a new module, but it is about $35. i have followed the schematics until my eyes fell out of my head. i am just wondering if say, the RF amp is shorted internally, will it also short the RX circuit? it would explain the lack of any RX signal.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  13. #13
    travis.farmer's Avatar
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    I have bought the RF power amp module. but it is the last chance for this radio, as i can't afford to pour too much more money into it. beyond this, i will just have to save up for a different radio.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  14. #14

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    Note that I was a radar tech and not a radio tech in the US Navy, but the RF amp shouldn't be in the receive signal path. It would pop the receiver.
    --
    73, Jim/N4AAB got my Extra class license on Aug 10, 2017. Vanity call in Oct, 2014.
    My Ham radio site has no popups, no music, no banners.
    'Through the thorns to the stars' from Ghost-in-the-Shell anime.

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    travis.farmer's Avatar
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    ...Your right, i knew that. I am just getting so frustrated with this radio. I may have to cut my losses and buy a different radio that uses most of the accessories i bought for my current radio. I have had my eye on a Kenwood TH-K20A. it doesn't look like it will break the bank, though i can't afford it at this moment.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  16. #16
    Super Moderator 5B4AJB's Avatar
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    You might find it is the RF PA, they can do strange things when overloaded/cooked, including messing with the RX...

  17. #17
    travis.farmer's Avatar
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    well, i did order the replacement RF PA module, so i will give it a try. beyond that, i am at a complete loss.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

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