The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Got this CB from a friend of mine ,(cobra 29Ltd) just plugged
it in a truck at work. apparently plugged wrong wires for power input,
truck had green & white wires in CB compartement .
CB was on at the time, then smoke started comming out of it, apparently
not a good sign , when i checked the fuse it was burnt out & wrapped
in foil paper, not good i guess ! Now it just keeps blowing fuses.

I guess my question is , is this repairable?
Can i use parts from 2 of my other non working CB's (cobra 19's) to repair my (Cobra 29Ltd).

Repair diagrams would be nice if possible!!!

Dansonic the results from some one rapping foil around the fuse and it being hooked up wrong usually isnt good but it is probably still fixable. First thing to check is the barrier diode should be located towards back of radio close to where power leads connect to the board usually this is the first thing to burn if it is replace it you should be able to use one from the other radios as you stated. Other things that may have been destroyed are the driver and final maybe even the audio chip.

You might also look for burnt components, also check the electrolytic caps inside where the power leads go into the radio. Man I can't believe that someone would wrap a fuse in tinfoil just to save 50 cents on a new fuse. It is mostly likely fixable , I had a basket case cobra 25 a few weeks ago and with Rick's help I was able to get it running . Ask Rick he will be able to help you out , if you follow all of his instructions , because he usually has the right answers.
Bob

Changed the barrier diode and tried it Works just like new
thanks. next step modifications thanks again thaught it was a gonner!!!

It's a good practice to replace the original 1 Amp-rated protection diode with one rated for more than the recommended fuse size.

A 3-Amp rectifier will probably survive reverse polarity with the proper 2-Amp fuse in line.

The original 1-Amp rectifier will not survive that 2-Amp fuse, and shorts internally from the heat. Like the last time.

On larger two-final radios, a 6-Amp rectifier across the power socket's pins will also protect the RF chokes between the socket and the radio PC board.

73

Fuses wrapped with silver foil or cigarette paper are a good indication that the set has been operated or played around with by someone who has absolutely NO ideas when it comes to electronics.

I've even seen instances of the fuses being taken out and replaced with screws, nails and other assorted conductive items.

Seen similar things done with TVs and other appliances but that's another story.

I personally don't like the idea of a reverse biased diode (crowbar) across the input. Too easy for people to reverse polarity a set resulting in blown fuses, blown diodes and more.
I take the diode out and fit a 6A diode in SERIES with the input. Sure, you lose 0.6V across the diode but if you are feeding your set with sufficient voltage, there's no real issue.

At least this way if the set is reverse connected, no drama. Nothing happens - no damage to any components, no loss of fuses (at the most inconvenient of times) or situations resulting in people doing silly things with silver paper.