Ok I recently as of Monday evening leaving work had the finals in my transmitter in my CB radio burn up. There was no noise but a strong smell of an electrical fire. At the time this happened the mic was not keyed up and was hanging on the side of the radio. I only talked on the radio once Monday and that was just a quick 5 second transmission to reply to a radio check.

Now with this in mind I asked what could cause this, number one cause is bad SWR. I tuned my Antenna last Friday as I finally got my meter in. After my linear is where I placed my SWR/Watt meter and found that with the linear on, on Ch 19 I was at 2.5:1 with Ch 40 being 3.0:1. I never talked on Ch 40 as I kept it on Ch 19 the whole time Ive had the radio being that is the highway channel.

Well I tuned the antenna and then cut an extra 1/4" off and SWR got worse but was able to raise the antenna in the holder to get Ch 1 to 1.5:1 with Ch 19 being 1.3:1 and Ch 40 being 1.7:1 with the linear on.

I honestly do not believe this is the case for this.

Another thing I heard was bad ground for the radio. Ive never heard of a bad ground causing an electrical fire. Has anyone here ever heard of that happening? Thing is though I just don't know enough about the internals of the radio to know but my assumption is the transmitter does not receive power till the mic is keyed up. Considering the electrical fire smell I smelled happened with the mic un keyed I am wondering if something shorted out internally to ground allowing more current to flow through a circuit in the transmitter than it was designed for and burned it up.

So what does everyone think? Is my line of thinking proper or could a bad faulty ground cause an electrical fire smell and burn up something electronic? I don't think so as I see cars daily at work with the battery cables so loose you can slide them on and off with no effort and the computers are not fried.

 

If you have a linear between the tranceiver and the antenna, then adjusting the SWR of the antenna would only affect the linear's finals, not that of the transceiver. It would be the input of the linear that determines the match between it and the transceiver's final output stage, not the antenna tuning.

Since you reported the tranceiver's finals burned up when the transmitter was not keyed, that suggests an internal defect in the transceiver or mic, not an external grounding issue.

 

Or something wrong with the input of the linear?

 

:shrug:

Pick one.

 

Well I mailed the Linear as well as the radio back to Bells CB in Flordia where I bought the radio from and had it modified.

I will wait to see what his findings are. He should call me though when he gets it so we can discuss what we will be doing. I hate to just pay $60 on upgraded Mosfet finals to wave the bench fee of testing it as I want to know exactly what happened so I can correct the issue or if the issue comes up again I know what it is.

I did not do a test between the radio and the linear mainly because the swr/watt meter built into this radio is not moving when I talk. When I key the mic up and talk the needle actually drops a little further down. Like wise using SWR/Cal if I try to calibrate the meter turning the **** to the max has zero effect on the needle. So I didn't bother checking between the two as I don't believe the meter would be dead in the radio but showing something different out the antenna.

Plus the radio when I put my nose to the openings for vents I could smell the electrical burnt smell inside the CB.

Only thing I can think of is the Mic screw nut was a little loose I noticed and I tightened it up on Friday when I went under the dash to hook up the watt/swr meter to tune the system. I have been told this could cause it but thing is I really don't talk much on the radio as I mainly listen so I have to find a wiring schematic to see how it works but surely a mic not being plugged in fully or not being plugged in at all would burn up the finals in the radio.

Guy with Rolling Radios the owner he told me its possible it could be a bad ground as something inside could be searching for another ground and burned a circuit up. Doubtful of that but I guess its possible. But he also told me it could also be the RX modifications I paid Bells to do that maybe a capacitor failed and shorted out to the TX circuit and caused this. I don't believe so because the radio still receives given its been very scratchy lately but that is probably due to all the weather we have been having lately.