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Cb radio reverse polarity damage

I have a cobra 29 that was reverse polarized,should i junk it or attempt to repair the diode?

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The diode is there to protect against rev polarity. Simply replace it with soomething like a 1n4007.


Posted on Mar 11, 2008


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I hooked up the power on my corba 29 ltd by and I think I blew something inside. Is this an easy fix?

The Cobra 29, like most CB radios, contains a reverse-polarity diode whose purpose it is to protect the radio against accidental reverse-polarity hookups. Normally all you will need to do is replace the fuse, then hook the radio up correctly.

If that doesn't get you going, then possibly the polarity-protection diode is now shorted and will have to be replaced (or removed - not recommended).

Beyond that, my experience is that the next component most like to get damaged is the Audio Output circuit, either an IC or a power transistor (larger than a regular transistor). At this point you're going to have to take it to a repair shop.

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d-23 is your reverse polarity diode.Change it and you'll be ok its a 1n4404

Oct 22, 2013 | Cobra 29 LTD CB Radio

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Cobra 29 ltd. turned rv4 switch and cb started smoking. what is the cause of this

if this is a used radio its because some golden screwdriver got into it but if its a new one then its the radio.Check the reverse polarity diode in either case to see if its burnt. If so replace it and see if it happens again.

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if you are talking about the reverse polarity diode its there , right by the power wires that come into the radio. way in the back on the R.H. side.

Jan 12, 2013 | Cobra 29 LTD CB Radio

1 Answer

What would cause my cb to blow fuses when u turn it on

d23 a 1n4004 diode second component from pa speaker port inside radio has failed. It is most likely that neg/pos polarity has been switched shorting this diode. It is there to protect your radio from reverse polarity as so it is names the "protection diode." 2 solutions first not recommended.

1. Cut the diode this will stop the directed grounding that is continuing to blow your fuse.
2. Go get a pack of 1n4004 and rosin core silver solder from radio shack and replace it paying attention to the direction it is installed.

just a side note the solder trace often burns in this area so a jumper wire soldered in around this bad area solder side maybe needed.

Jun 30, 2011 | Cobra 29 LTD CB Radio

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It blows fuses when u plug the power cord up

The radio was probably wired backwards at some point. There is a reverse polarity diode inside that must be replaced to fix this. If you have continued replacing fuses and plugging it back in, there may be further damage such as finals or audio amplifier chip as well. you will need to take the radio to a qualified repairman for service. If it is simply the reverse polarity diode, your bill should not be more than an hour's labor charge.

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Sounds like it has reversed polarity damage, hooked backwards on the red and black wires, blew the polarity diode and needs a technician

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3 Answers

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For 25 cents, they could have installed a diode to prevent this problem, but now there isn't anything you can do, as the damage has been done by the reverse polarity.

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