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Cobra 29 LX Not Turning On Low Voltage

Discussion in 'General CB Services Discussion' started by 5.0 Wrangler, Sep 30, 2014.

  1. 5.0 Wrangler

    5.0 Wrangler New Member

    Sep 30, 2014
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    I owned this CB new for about 3 months then I accidentally let the battery drain on my Jeep when I left my interior light on. The radio was off but made a clicking noise from the speaker, I unplugged the radio and plugged it back in but it will not turn on.

    Fast forward several months, I am trying to figure out what is wrong.
    I have the wiring, and solder diagrams. Access to a soldering iron, solder and digital multimeter.
    I replaced the diode between C123 and C124. I tested the original diode and it is working great with no continuity.
    I tested all the components before the switch and they seem to be good.

    When I remove the yellow wire from L201 from the back side of the plug connector, the back of the + and - plug terminals read 12v.

    As soon as I touch the yellow wire back to the positive terminal I get a reading of 2.75v
    I checked the red wire at the switch and that is also 2.75v.
    If I remember correct the orange wire at the switch was 1.3v.
    My guess this is some kind of voltage regulator issue.

    My problem is the electrical diagrams are not a detailed as automotive diagrams.
    For example I had to look at the solder diagram, electrical diagram and the CB itself to figure out from T2 the power goes to the Black W20SW wire that is soldered on another board that makes contact to a Red wire that goes to the power switch. The Cobra diagram shows a connection from T2 to the switch.

    Is there an electrical diagram out there that is more clear?
    Also does anyone have any ideas to help me out?

  2. Robb

    Robb Yup

    Dec 18, 2008
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    5.0 Wrangler likes this.
  3. 5.0 Wrangler

    5.0 Wrangler New Member

    Sep 30, 2014
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    Thanks for the link Robb.

    That is the exact link I was using and I was reading it correct. My frustration got the best of me. After I slept on it and really thought about the problem, I realized my answer was in the first post. Normal voltage with no load and low voltage with a load at the same test point. DUH!

    If you are following along and still don't get it.
    Here is a good read on what basically happened to me and how to test for it.


    Even though my voltage and resistance reading was good the wire did not have enough capacity to provide the power the radio needed.

    A month after I bought the CB Radio, I went to Moab and it just so happened my horn wiring grounded out and caught on fire. (previous owner tacked on a horn really quick for SAFETY inspection without a fuse. Ironic huh?) I remember part of that wire melted and stuck to my CB wiring. I checked it really quick and did not see anything and my CB worked so I did not worry about it.

    Lesson learned. Any damaged wiring needs to be replaced.
    A new plug from the Flying J fixed my problem.
    At least I learned about my radio and was able to practice soldering.
    Even picked up another one for $40 on KSL for a backup. Life is good.

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