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Hi I have A Cobra 29 Chrome ED. that was plugged in backwards and I would like all the information on replacing the protective diode. Also I would like to learn how to replace the burned out light meter blub and replace it with a new LED blub. Can You Also Show me how to replace The red channel selector to a blue on a cobra 29 LTD? Thanks John

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The protection diodes are D23 and D8. they need to be replaces with N14003 or bigger. they are near the back right of the radio near where the power comes in by the transformer.

changing the channel selector screen is just unsolder the old one, and solder in the new one. Getting to where to solder it is a pain. You have to take a lot apart.

Posted on Oct 10, 2009

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1 Answer

How do i find and replace the finals in a cobra 29ltd classic

The protection diode (a black, tub looking devise) hooked to the positive power wire near the back of the radio, is most likely your problem. Check to see if any doides are shorted by using a Volt/Ohm Meter by checking for a short. For more imformation or help, email me at
"Original Radio Man"

Jan 01, 2013 | Cobra 29 LTD CB Radio

1 Answer

How to check wiring inside a cobra 25 classic to determine if its made propperly

Yes, if you have a meter check resistance (like reading a fuse) with the radio off and power cord removed.

Only two of the three pins (look at power cord to see only two have metal in them) are used.

With power switch on front in off position there should be no reading across the + to - pins on the back of the radio.

If a short there the protect diode is shorted--likely first time it got hooked up backwards--easy to do.

Follow in this case the + pin on back just inside the radio and it goes directly to a diode. cut the diode if a short there and read again at the plug--if short gone replace the diode--radio will work without it but you will have no protection in that case.


Jun 02, 2012 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29 nhst d8 blown

Check with a ohm meter for a short to ground on that diode.

If it is the protect diode at the power plug the unit likely got hooked up backwards to power.

A dead short there with the diode removed indicates a short---start disconnection of parts before and after the power switch to locate it.

Mar 22, 2012 | Cobra 29 LTD CB Radio

1 Answer

I have a cobra ltd 29 chrome edition that is not getting any power when you turn it on

Before you had this problem, did the power cord accidentally get plugged in backwards?

If this is the case and the inline fuse on the power cord blows everytime it is plugged in correctly, then more than likely your protection diode is blown.

This is not typically the end of the world for a cb radio. If all that happened is the diode blown, it is a 10 cent fix if u do it yourself, and a $10 fix if you take it to a cb radio shop.

If you feel comfortable opening up your radio and you want to verify this is the problem, then remove the cover from the bottom of the radio (the one with the speaker holes.

In the back right corner of the radio locate D23. This is the protection diode. Sometimes when it blows, it will actually fall apart, and sometimes it will just crack.

Another test, if you have a multimeter, set it to read resistance. Before doing this test, make sure the power cord is removed from the radio, and then cycle the power potentiometer on and off (this will de-energize all of the capacitors. Now, connect one lead to the positive pin and the other lead the the negative pin of the power socket at the back fo the radio. If the protection diode is blown, you will read a direct short. If the protection diode is still good, you will read over a couple hundres ohms (mine is reading 582.1 ohms right now).

If you find out that the protection diode is bad, and you want to try and tackle the repair yourself, you can email me and I will send you complete instruction guide I created a few years ago for another member.

Dean Pitts
Rollin CBs

Feb 26, 2012 | Cobra Radio Communications

1 Answer

Cobra 29 nite watch hooked power wires up backwards witch diode is blown

there is a diode on the power line that blocks the dc to ground. follow pwr wires down to board. and the first diode on the + pwr is it. this is on all radios. and not just cbs. just put a new diode on the back side of the pwr plug. were the wires solder onto. but even better what we do @ our shop 254.718.4042 is use or make bridge rectifier install inline. and you will never have that problem either direction you plug it in. will work. no more worries about polarity.

Dec 15, 2009 | Cobra 29 LTD CB Radio

2 Answers

Blowing fuses when power is hooked up

once you've done this, hooked up a radio backwards, you have to change the resistor...take it to a shop I only charge $18

Nov 26, 2009 | Cobra 29 LTD CB Radio

1 Answer

Have cobra 29 nw ltd keeps blowing fuses inline and in cigarette lighter adapter adapter is 10 amps and inline is no more than 5 amps

This is an easy fix if you are comfortable soldering.

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.

  • Go to radio shack and buy an N1004 diode.
  • Open the radio
  • Look towards the back right of the radio for a black diode D23. it will probably look burnt, but not always.
  • Use a soldering wick to remove the solder holding the diode in.
  • Remove it, and replace the diode making sure its going in the same direction as the old on. Strip on the side the triangle is pointing.
  • Solder it in.
  • Test the radio
That should do it.

Make sure you are careful to hook the radio up to power corrctly.

Nov 14, 2009 | Cobra 29 LTD CB Radio

1 Answer

Im a trucker so when i plug my power wire the fuse blow why

You probably plug it in backwards at some point. When you do that you blow the polarity protection diodes. They are so you do not blow the radio.

Get a N14003 diode from radio shack.

Open the radio's bottom cover where the speaker is. Watch the speaker wires.

Near the back right of the board where the power cord plugs in left of the transformer, look for D23. Its the same diode as the one you bought from radio shack. It is most likely burnt.

Remove that one and replace with a new one.

The radio should work fine now. Be careful when plugging that thing in.

Oct 11, 2009 | Cobra 29 LTD CB Radio

1 Answer

Blowing fuse

Your polarity protection diode has been blown. If you tried hooking up your CB and accidentally pushed the plug in backwards. Inside the radio, there are 2 big black diodes near the transformers, D8 and D23. Replace these with the same or bigger. You can the burnt one out and the radio will work, but if you hook it up wrong again, it will fry the radio.

May 02, 2009 | Cobra 29 WX NW ST 40-Channels Base CB...

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