Question about Cobra 29 LTD CB Radio

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When i hook up my cobra 29 Ltd to my pickup it keeps blowing fuses, red to postive and black to negative..Cannot figure out whats wrong

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You have hooked your power wire up backwards at some point and blown the polarity protection diodes.

This requires opening the radio and using a soldering iron to remove and replace the blown diode.

You will need:

  1. Soldering Iron
  2. Solder
  3. De-soldering braid
  4. N1004 diode or better.
  5. Phillips head screw driver.
Using the phillips head screw driver to take the bottom cover of the radio off being careful of the speaker wires. Using the soldering iron, heat the solder on the tabs of the speaker and pull off the wires. No need to use the de-soldering braid to remove the solder. You should do this to make it easier to handle the radio, and to avoid damage to the speaker or wires etc.

Now take the cover off the top of the radio. This will reveal the "Trace" side of the board. This is where all of the components are soldered to the board.

Now flip it to the other side where you can see all of the components and wires etc. Look at the back right of the radio by where the power socket is. Look for D23. its a big black diode. It will most likely be black and burnt. Some times it may not be.

Here is the tricky part. You need to locate the points at which this component marked D23 is soldered to the trace side of the board. Some times you can use a bright light and look at the trace side of the board while the light shines on the other side to locate the part.

Once you have located the points at which the diode is soldered too, do not de-solder it yet. Make note of which side of the diode the white band is on. This is important, putting the diode in with the wrong polarity will make the radio not work.

After you take note of the white band you may now use the de-soldering braid to remove the solder from the trace side of the board. To do this, place the braid over the solder point. put the tip of the soldering iron on the braid and press it down to the solder point. You will see it **** the solder into the braid.

Once the solder is off both solder point, flip the radio and remove the bad diode.

Put the new diode in, making sure the white band is on the same side as the original diode.

Once again flip the radio over to trace side of the board and solder the new diode in. To do this place the tip on the solder point, making sure to touch both the solder point of the board and the wire from the diode. take the solder and touch it to the solder point, not the soldering iron tip. Once enough solder is on the point you can remove the soldering tip. Don't use too much solder.

Once both points have been re-soldered, solder the speaker wires back to the speaker. Red is positive, it connects to the tab marked by the positive symbol "+". The white wire is negative. It goes to the negative symbol, "-". You can just reheat the tab, and put the end of the wire into the melted solder and remove the solder tip while holding the wire in place until it cools enough harden again.

After the speaker is re-soldered, Put the covers back on. Now be very careful hooking up the radio to power. If you hook it up backwards again it will blow the diode again. Once the power wire is connected, turn on the radio, it should work fine at this point.

Good Luck!

Posted on Oct 07, 2010

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