Question about Cobra 25 LTD 40-Channels Base CB Radio

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Fuse each time i connect power to my cobra 25 it blows the inline fuse, any advice or help would be great

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  • drive1951 Feb 13, 2008

    i am trying to locate a reverse protection diode

    for my cobra 25 cb, can't read the numbers off bad diode

    anyone who knows where to find this diode and what numbers to ask for. and would like to extend my thanks to BENIMUR>>



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There are only a couple of components that could cause the fuse to blow. They are:
1. Reverse protection diode (D23)
2. filter capacitor (C123)
3. Outputs (TR14 & 15)
4. Audio Amp (IC4)
5. Zener Diodes (D22 & 19)
6. the fuse itself (it should be 2 Amps

Hope this be of help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Thank you for using FIXYA.

Posted on Feb 12, 2008

  • Louie  Role
    Louie Role Feb 14, 2008

    Hi again drive1951 ,

    Appreciate the update and you're more than welcome. Am glad to be of assistance and appreciate the rating too.

    Though I have to correct myself. Initially given numbers were for a Cobra 29, the PCB part numbers for the Cobra 25 LTG should be:
    1. Reverse protection diode (D17)
    2. filter capacitor (C65 1000uF/16V)
    3. Output/Driver (TR7 2SC2075 & TR8 2SC1957)
    4. Audio Amp (IC1 TA7222AP)
    5. Zener Diodes (D13 & 15)

    To your 2nd post > location of D23/Reverse Protection Diode
    it is often across the power connector terminals rear end inside the unit. In some other instances, it is soldered to the PCB but still very near the power connector. It would be the only biggest diode inside. Another indicator that it is bad is when the fuse blows even if the radio is switched off.

    To your post > can't read the numbers off bad diode
    depends which diode:
    D17 - 1N5400 or 1N4003 or SR1K1
    D13 - 5.1volts
    D15 - 9.1volts



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What size fuse is used in COBRA 29LTD CLASSIC radio.

First question should be, what happened to the last one? If the fuse blew on you, you need to find out why. If it was just missing when you got the radio...

That said it is surprising that the manual doesn't state this value directly. However, it is a 4W transmitter and the manual I referenced states that you should connect to an "accessory" fuse for mobile installation. My car has a 10a fuse in that position but a 3A slo-blow in the power wire's inline fuse holder should do the trick. (The main reason for using the "Accessory" fuse is for operation with the engine off, but not battery drain unless the key is inserted.) Another clue for my SWAG is that for a "base station" installation, the manual recommends a 12Vdc power supply that can deliver >2A... So I think we are in the ballpark.

If you have lost your original manual you can get a replacement from the Cobra support site here:


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You must have hooked it up backwards. Big problem when using a cigarette lighter adapter. You have to be careful, if you hook a radio up backwards you blow the polarity protection diode.

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I had the same problem with a 25 that was just disconnected for replacement. I found a shorted diode right where the power cord came in. I also didn't like the way the electrolytic capacitor right next to it was charging so I changed it also.
Problem solved.
I am sure the 29 will have a similar setup. I you want I will look up my schematicof a 29 and tell you the numbers to check.
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