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Cobra 29 LTD Classic Problems : Weak Receive, No Transmit

Discussion in 'CB and Export Equipment and Accessories' started by office888, Jun 8, 2009.

  1. office888

    office888
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    Hello,

    I'm pretty not new to CB radios, but I am new to fixing them.

    I got a Cobra 29 LTD Classic off of a friend of mine. It powered up okay, the display only works on bright, but I didn't think it was a huge problem.

    I tested it a spare antenna and with my existing car rig (Cobra 19 + Wilson Antenna). The Cobra 29 receives very poorly. Sound is very weak and full of static when I key. Even with squelch all the way off, and gain all the way up, I still can't get the speaker to produce any regular static.

    Transmit is another story. When I key, I hear the pop of the key activating and my Cobra 19 goes silent like someone is transmitting, but it won't transmit any of my voice.



    Help?

    Thanks,
    Richard
     

  2. Moleculo

    Moleculo
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    Sounds like it could be the audio chip. Can you test the PA function?
     
  3. office888

    office888
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    Just tested it, no output at all.

    Bad audio chip then?

    "NPC 9222
    D2816C" - the audio chip?

    Also, would it interfere with anything if I removed the internal speaker and replaced it with a small 12V-switched fan? I wanna peak&tune this unit to get a bit more "umph" out of it. I've been into computers for a while, and I know heat is the bane of electronics.

    It's going to go in my 90' Audi 80 "Wintertastic Rallybeater" with a Wilson-1000 probably.

    -Richard-
     
  4. office888

    office888
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    One other thing, the onboard meter does not work at all. Not sure if that affects anything?

    -Richard-
     
  5. Moleculo

    Moleculo
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    No, it's IC4 - TA7222AP or something similar. You don't need the fan anyway if you're going to peak it out - even if you do a more extreme mod like a 50 watt FET. The final transistor is mounted to what is effectively a big heat sink. If you really want to add a fan, you could wire it to 12v and mount it on the back/top, but run the power leads through a small ferrite torroid a few times. If you don't you'll get nasty motor whine in the TX/RX.
     
  6. Moleculo

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    Fix the audio amp first, then try the meter. It could be out or just stuck. If it's stuck, carefully lift up the tape on the top of the meter, apply a tiny drop of oil on the screw and turn it carefully a little bit. If it still doesn't work, you'll need a new meter - they aren't expensive.
     
  7. office888

    office888
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    That took a bit of searching, weird hiding spot on the side...

    Surrounding the TA7222AP is a bunch of white powdery crap. Solder joints are more "hilly" than the rest. Looks like it might have been replaced before?

    Regardless, $5.25 part, going to go ahead and replace it anyways.

    No fan it is then!

    Thanks for the help, we'll see if that's the issue.

    -Richard-
     
  8. Blackbox

    Blackbox
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    I had this same problem with a radio that I just picked up. I'm no professional, but i found the problem. On mine, there were a handful of solder connections that were busted loose on what I assume to be the transmit chip. I re-soldered those connections, and it started working great. I still don't have the onboard SWR meter working. Not quite sure whats up with that yet. Good luck.


    *Edit: I just realized this was a dead thread... oops!
     

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