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Cobra 29 lx (new digital display) no power

No power.. plugged it in, the radio went on and off real quick. checked pos. and neg. they were good. plugged pack in, and the radio, again flashed on then off. thought it was a fluke.. dummy me... try it a 3rd time. all I got was a little smoke out of the back of the radio.

Posted by Hock on

  • Hock May 20, 2012

    Thanks.. I had the diode was replaced, but come to find out the PCB (printed circuit board) had a burn mark in it. and was unrepairable. Well a $150 radio is now a paper weight. I guess I'll go back to my oldie but a goodie15+ year old cobra 25



1 Answer

SD Tech

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  • Master
  • 14,553 Answers

With no power connected read resistance across power leads---likely protect diode just inside back of radio from red power lead is shorted to ground



Posted on May 19, 2012


4 Related Answers

One Wire

Dean Pitts

  • 126 Answers


When you reversed the polarity of the power and negative, if it did not blow the inline fuse, then all you did was burn the protection diode. Sometimes it can do more damage, but usually its just the protection diode that goes. They are a cheap fix and if you have a local cb shop, tell them what you did, and they should, repair it for $10 to $15. If they try to charge more, then they are trying to rip you off. If you don't have a cb shop to go to, and you can unsolder and solder components on a pc board, email me at [email protected] and I will walk you through re-placing the diode. The diode can be purchased at Radioshack.

Rollin CBs
Mt. Vernon, TX

Posted on Jan 25, 2008



  • 2130 Answers

SOURCE: wired backwards

In many CB's there is an internal diode that is connected across the DC line. When the power is connected correctly, the diode is reversed biased and does not conduct. When the power is swapped, the diode is forward biased and conducts. When that happens, it causes the in-line fuse to blow. Was there an inline fuse in the power leads? I would take the cover off and see if there is a burned diode where the power cord enters the radio. Take a look and see what's burned. Let me know what you find and we'll go from there. If there has been a lot of damage, it may not be worth fixing.

Good Luck,
- Jim

Posted on Jan 28, 2008


  • 1 Answer

SOURCE: cobra 25 ltd wx wont power up

You most likely blew a Diode that is back near the power plug.

It is easy to fix the diode but if you continued to apply power you may have damaged other parts including the audio chip.

Posted on Jan 02, 2009


Michael Thomas

  • 3053 Answers

SOURCE: Hello there

Hello there
If you remove the screws that hold the top cover on
and remove the cover look by the front of the unit and you will see a small inline glass fuse (50x250) .
simply remove this fuse and replace it with a new one
also check all of the other fuses that is going to the power cord too ok
I hope that this has helped you out a lot
best regards michael

Posted on Nov 13, 2009

Testimonial: "wow that did it sorry it took so long to get back to you went to the radio shack and got the fuse now all is well love this radio"

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Just received my new cobra 29 lx cb. When I turn on the power the radio comes on for about 2 seconds then the screen goes blank and all fuctions cease. When the power to the radio is turned off, the screen...

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1 Answer

Oem Radio installation

*** 91 park ave with delco bose =

black = ground
dark green = lights on input
grey = panel lights
pink = on input
yellow = power input
orange = battery power input

nca = shield ground
tan = left fr spkr +
orange/black = left & right spkr -neg
lite green = right fr spkr +

nca = shield ground
dark blue = right rear spkr +
dark green/yellow = right & left spkr - neg
brown = left rear spkr +

purple/white = display dim output
pink = vehicle speed input
**** 91 park ave without delco bose =

purple/white = display dim output
pink = vehicle speed input

grey = left front - neg
tan = left front + pos
dark green = right front - neg
light green = right front + pos

black = ground
dark green = display dim signal
grey = panel lights
pink = power antanna
yellow = ign input
orange = battery power
light blue = right rear - neg
dark blue = right rear + pos
yellow = left rear - neg
brown = left rear + pos .

there YA go

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1 Answer

Cobra 25 ltd wx wont power up

You most likely blew a Diode that is back near the power plug.

It is easy to fix the diode but if you continued to apply power you may have damaged other parts including the audio chip.

Dec 22, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

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