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Cobra 25 Ltd Classic getting hot

Discussion in 'CB Radio Forum' started by Leeworthy, Sep 17, 2013.

  1. Sep 17, 2013 #1
    Leeworthy

    Leeworthy Bobtail Member

    49
    12
    Jul 8, 2012
    Belleville, Ontario
    0
    Hey guys and gals,

    I am trying to do some work to my Cobra 25 Ltd Classic that I just picked up used for 10 bucks.

    I noticed today that there was a burning smell coming from the radio while plugged in and transmitting. I used my infrared thermometer and narrowed it down to PL C96. I am trying to look at a schematic to figure out why it is getting hot and what it is exactly.

    Now, two questions, the antenna I am using is NOT grounded, it is just a truck mount one and I have it sitting on my bench just so I can key up. Could this be the problem that is causing this to heat up? Also without the antenna grounded I know my SWR are going to be very high, could this cause that as well?

    Any insight from the minds would be greatly appreciated.

    Thank you
     
    Leeworthy, Sep 17, 2013
    Leeworthy, Sep 17, 2013
    #1
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  3. Sep 17, 2013 #2
    kc0iv

    kc0iv Light Load Member

    294
    233
    Mar 31, 2010
    Parkville, Mo
    0
    First I'd say there is a good chance it may be the problem.

    Secondly, I would suggest you use a dummy load while bench testing output signals.

    Leon
    (kc0iv)
     
    kc0iv, Sep 17, 2013
    kc0iv, Sep 17, 2013
    #2
  4. Sep 17, 2013 #3
    Leeworthy

    Leeworthy Bobtail Member

    49
    12
    Jul 8, 2012
    Belleville, Ontario
    0
    Hey Leon, thanks for the info. I want to pick up a dummy load, but just getting into CB's and have no shops around where I live. So would have to order one online somewhere. Been picking things up slowly, Jana HJ8056 SWR/Modulation/RF meter, Frequency counter, power supply.
     
    Leeworthy, Sep 17, 2013
    Leeworthy, Sep 17, 2013
    #3
  5. Sep 17, 2013 #4
    Pilgrim007

    Pilgrim007 Light Load Member

    125
    80
    Sep 9, 2013
    0

    Never key up or attempt to operate your CB without a working antenna or "dummy load" (non-radiating antenna simulating device) connected to the radios antenna jack, unless you have extra money to buy another radio, or know a good repairman.
     
    Pilgrim007, Sep 17, 2013
    Pilgrim007, Sep 17, 2013
    #4
  7. Sep 17, 2013 #5
    Leeworthy

    Leeworthy Bobtail Member

    49
    12
    Jul 8, 2012
    Belleville, Ontario
    0
    10-4. will look at getting a dummy load online this week.
     
    Leeworthy, Sep 17, 2013
    Leeworthy, Sep 17, 2013
    #5
  8. Sep 18, 2013 #6
    Ridgeline

    Ridgeline Road Train Member

    22,636
    120,654
    Dec 18, 2011
    Michigan
    0
    Congrats, good radio and good price.

    I don't see a PL In my parts list for that radio but depending on which board, there is a c96.

    OK Are you sure it was c96?

    What did it look like?

    Well it can be a problem, as suggested, I would just use a dummy load from Radio Shack if they even have them or some other place.

    Not if it is c96. It will cause the radio to have a short life for the final but that's about it.

    I am going to assume that the part is c96, so here is what I think.

    Yes I am thinking the capacitor (that's the c in c96) is going bad - starting to short. If all the schematics I have are correct, it serves as a filter to the the final mic amp before the final big amp, and there is a voltage on the output of that final mic amp which connects to one side of c96 with the other going to ground. If it is shorting, when you transmit, voltage will heat it up and then burn it, many of these have a small wax coating on them and that may be what you are smelling.

    Hope that helps narrow it down.
     
    Ridgeline, Sep 18, 2013
    Ridgeline, Sep 18, 2013
    #6
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