Question about Uniden PC78ELITE 40-Channels Base CB Radio

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Power was reversed now radio keeps bowing fuse and will not come on

The power was hooked up backwards on a uniden 76xl cb can you tell me how to fix or where the pertection diod is on radio

Posted by kenny hubbard on


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Dean Pitts

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Most cb radios have protection diodes that are made to burn out to save the radio in this situation. Usually you can replace them with a rectier diode between 1n4004 and 1n4008. They can be purchased at Radio Shack, or if you need more stuff, you can get them from Parts Express. This unit is the same as a cobra 29. If the pc board layout and numbering is the same, then the protection diode number is D23, which is located in front of the pa speaker jack on the main pcb. If you need more help, feel free to email me at [email protected].

Rollin CBs

Posted on Jan 26, 2008

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  • Dean Pitts
    Dean Pitts Jan 26, 2008

    Rectifier, not rectier

  • Dean Pitts
    Dean Pitts Jan 26, 2008

    I can possibly gain access to one of these radios, if a customer of mine still have it. If so, I will open it up and find the actual number of the diode for you.

  • Dean Pitts
    Dean Pitts Jan 27, 2008

    I opened up and looked in a 76XL today, and I was correct. It is exactly the same as a Cobra 29. The protection diode is number D23.




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Hello hubcap,


When the power was reversed this shorted out one of the components, possibly an Operational Amplifier. This tells me that there is no diode protection and possibly the circuitry is exposed directly to the input power supply. The fix would be to find the shorted component with the use of a schematic and a multimeter. Once you correct the shorted component then if possible you can add diode protection by putting a diode (forward biased direction) in the path of the positive line.


Again you will need a schematic, and a multimeter to work on this problem.


I hope this helps,


Thank you,



Posted on Oct 15, 2007


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