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Discussion in 'General CB Services Discussion' started by Ziploc, Aug 31, 2021.

  1. CorruptHawkeyez

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    I just read back thru it 3 times and have yet to see anywhere you posted that it's a comp cobra 29. (maybe I'm going blind) if it was posted I apologize.


     
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  2. nomadradio

    nomadradio Analog Retentive

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    Keys up.

    Gives you power for a moment, then goes dead.

    Bad D8?

    Intermittent bipolar final transistor?

    Driver transistors can fail, but far less often than finals.

    Not gonna get many questions answered about what's shutting down without a few measurements.

    73
     
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  3. 144inBama

    144inBama Sr. Member

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    I'm going with a bad solder joint then. If you're still transmitting fine and only your TB and needle are failing, it sounds like you are losing a connection somewhere. Time for the magnifying glass and a good light....IMO anyway. You can also check the values of the TB circuit components to make sure they're in tolerance.

    Screenshot 2021-09-12 050108.png
     
    #18 144inBama, Sep 12, 2021
    Last edited: Sep 12, 2021
    NZ8N, Ziploc and Shadetree Mechanic like this.
  4. Ziploc

    Ziploc Well-Known Member

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    Yeah I didn’t
    Thanks
     
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  5. Ziploc

    Ziploc Well-Known Member

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    It’s still is transmitting I lose needle and sound of talk back mid sentence
     
  6. 144inBama

    144inBama Sr. Member

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    If you just hold a dead key for a few seconds then speak, does it still cut out in the same time frame? Is it shorter, longer? It's possibly a bad/weak cap in the circuit. When you modulate the cap can't keep up so it goes open and you lose everything, then when you unkey it allows it to cool and charge....just spit balling here. C76 and C52 are the two I "think" I'd look at.
     
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  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I'm thinking D21 by Main Regulator - communication from TR21 is lost so it doesn't stay keyed up...

    You lose Audio from the loss of speaker return (you're in TX)

    upload_2021-9-12_9-54-26.png

    And lack of communication may relate to R101 2.2ohm resistor to PTT swtich.
    Pin 3 on the MIC.
    upload_2021-9-12_9-56-59.png
    You haven't answered my other question ...

    Do you get a TX light?
     
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  8. Ziploc

    Ziploc Well-Known Member

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    Tx light is on yes. It happens whenever it wants . I lose talk back sound needle dies however my people still hear everything I’m saying on the other end. Tried different mics amp on or off same
     
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Talkback eh?

    The mods done to make the Talkback work, is that effort.

    IF you're getting out signal and the needle dies?

    Something in the rework is not holding up to your expectations...let alone needs...

    Then - by your word...

    This isn't the radio , it's the interface layer between the radio and all your accessories Talkback, the Amp keying circuit - I would suspect being the problem - a simple power cap holding the charge, that when you start to "chat" it drains off - but because of the TX and what appears to be the radio itself seems ok then - your techs work to give you talkback and any external controls thru that work, it seems to be the source of this problem.

    A simple relay and cap circuit can do this - if you replaced the relay with one that didn't wire up right or has a different ohmic coil impedance/resistance (coil ohm or draw rating) can also do this for the loose wiring or socket, or relay itself - everything done to "chat" with talkback on and relay interface is suspect right now.
     
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  10. Ziploc

    Ziploc Well-Known Member

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    I’ll let y’all know more tomorrow. I turned off the TB it’s ran to the cb/pa switch and hasn’t done it yet. Might just be coincidence, I’ll let you know ratchet jawing this week
     
    Slowmover likes this.
  11. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    You loose indication of modulation, but everyone still hears you?


    Wow, that certainly puts a nail in "you are the common denominator of all your problems". Yeah that's got to be a cap taking a dump. In my humble opinion of course. That is a problem that I have not read about yet, as I have read about a lot of problems and the fixes in my short time here. Interested in what the fix is.
     
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  12. Ziploc

    Ziploc Well-Known Member

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    Dustin will know
     
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