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Cobra 29 nw ltd classic, no receive.

Discussion in 'General CB Services Discussion' started by Ay589, Dec 5, 2016.

  1. Ay589

    Ay589
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    Hammerjockey Radios

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    I know there is probably a page in here somewhere explaining how to fix my machine, but I cant find it, (New here) Only thing I have found was to remove TR-13 to see if audio comes back, I did and the receive audio comes back somewhat. After this, I don't know where to look, pin 11 on the ic is 4.96 volts, Any help would be greatly appreciated, I am into the hobby and want to get much further into it! I know the cobra 29s arent very sought after by most, but i like it as a slip seater radio thats plain and simple! I could go buy one, but I am tired of this disposable world we all live in, I rebuild trucks, machines, etc, guitar amplifiers, why not rebuild cb's and amateur radios too! 73


     

  2. LeapFrog

    LeapFrog
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    Dumb question, but do you have a microphone attached to the radio, if so do you have another microphone to swap and test with?

    These radios generally need a microphone attached for the receive audio to come through, sometimes one wire can break loose from inside the four pin plug connection on the wire harness of the microphone and it will cause the receive to go out if this happens.

    That's why I suggest trying a different microphone.

    Do you have an external watt meter?
    Do you have more than one CB radio?
    I'm asking these questions because I'm curious to know does your radio transmit (is the PLL locked?)?

    How did you confirm that you still have transmit but no receive?

    The tr13 tidbit might be a dead giveaway to an experienced technician, I'd have to dig through some computer files and re-examine the schematic, even then I might not be able to give you a direct answer.

    Does the public address function work with an external speaker? (is audio I.C. Functioning)
    Also have you tried connecting external speaker I have come across a few older Cobras where the internal speaker died, use a d.m.m. to confirm that you do not have an open circuit between the two speaker leads, if the speaker test open circuit in the coil has failed.

    Somewhat unrelated but does the S meter move about when you should be hearing another station?


    -LeapFrog
     
  3. Ay589

    Ay589
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    Honestly I have done every one of those steps. And nada. I have plenty of radios around to listen and rx back and forth, watt meter etc. doesn't show output in meter
     
  4. LeapFrog

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    So just to be clear, you are 100% certain that your Cobra can transmit?
     
  5. Ay589

    Ay589
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    I can transmit and it will recieve on another unit. No watts coming out but audio is coming through from my mic
     
  6. LeapFrog

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    No watts coming out, & and the receive doesn't work?
    My friend it sounds like your radio has more than one issue!

    Oh boy! It can be very difficult to diagnose radio when not in front of you. Someone with more experience is going to have to chime in here.
     
  7. loosecannon

    loosecannon
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    ay589.

    so, you can transmit, and hear your voice on another radio. correct?

    does the S-meter move to the right when signals come in or is it dead?
    LC
     
  8. Sideways

    Sideways
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    I just repaired a 29nwstwx with a seemingly similar issue.
    TX worked as it should and WX worked. Rx signal and audio, worked..kinda, but was very very faint.
    One of the rx tuning cans, I assume, had a bad solder joint. I could press on the cans with my finger, and rx would return. I resoldered the whole area of L4-L5-L6 and the crystal FL-1? IIRC, and cured the issue.
     
  9. Ay589

    Ay589
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    Ok. I've been playing around with 3 different radios. I took a 1969 final from another dead 29, it now puts out 3 watts, have very little distorted tx audio picking up on a good radio here, still no rx what so ever on this 29, needle moves as it should, in rx and tx. Now I'm wondering where to move next
     
  10. Ay589

    Ay589
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    When I remove transistor tr-13 my recieve comes back very very little
     
  11. kaos513

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    I would start testing all diodes in the recieve section of the board,then really look goodon the board for any bad solder joints.
     
  12. LeapFrog

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    Sounds like a bad audio I.C., how is the P.A. audio quality?
     
  13. Ay589

    Ay589
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    I cant test pa, while the radio was working good, I had removed wiring for pa when I utilized the switch for another purpose to turn power on and off for my 203 stinger board, (which worked flawlessly by the way), I never use the pa function so said, screw it, heres my spot instead of drilling a hole to add an ugly switch! soldered the w39 blue wire to w40 on the board to complete the tx circuit as a 1" wire now. everything was fine with all of that for months.
    My whole problem started when i was removing a resistor the previous owner had on the pa/sp jack for talkback (which i hate and could not deal with any longer),I powered back on to test with covers off, radio worked perfectly!! Put the mic down, slipped and the board touched a pair of pliers on my bench and it went silent ever since. with tr13 removed I can just hear recieve and tx is full power but low audio and distorted. Sorry for repeating
     
  14. 222DBFL

    222DBFL
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    Check all the traces as well going through the audio section. Maybe you burnt a trace somewhere. Other than that I would do what these guys are telling you. They know about radios. Also posting some pics of both sides of the board would help a lot. I'd about bet someone will find the issue if they had some good photos to look at. Many issues have been solved this way!! Just some food for thought. Hope you get it resolved. Love my cobra 29LX LE with a 1969 final in it. It rocks for an AM only radio. Nice receive ad well, for a CB radio.
    Anyhow. Again, hope you get it resolved. But seriously post some pics up and I wouldn't be surprised if someone finds the issue.
    73 and God Bless.
     
  15. Ay589

    Ay589
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    I've done everything they're recommendinbesides remove each diode resisor capacitor and l test. Can't really test them on the board because resistance gets put throughout it right?



    Still though. I read 3 places about "removing tr13 and if audio comes back " and they don't go any further on the subject. What's the next step from that, gotta be headed somewhere in the right direction. I replaced tr13 with new but no fix.
     

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