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Cobra 29 CB Help ???

Old 10-17-2017, 10:21 PM
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Cobra 29 CB Help ???

I have a three-year-old Cobra 29 WX NW ST that I bought new; bone stock.
This radio has performed flawlessly until just a couple days ago.
Antenna is the big Wilson 5000 Trucker, mirror-mounted with the big barrel coil-spring under it, with auxilliary grounds including a dedicated ground cable through the door and into the under-the-dash to a solid well-grounded surface.
SWR was tuned and calibrated by a good external meter.
It is connected to the highest price Cobra speaker, the noise cancelling one with talk-back.
The mike is the one that came with the radio.
It is connected to an external PA horn-type speaker and the PA works perfectly.
The weather channel plays loud and clear through the Cobra speaker.
Everything lights up.
When I key the mike, the green light turns red, release the mike and it goes back to green; however, the needle does not move at all.

However, I have no CB response whatsoever.
With noise limiter OFF, squelch all the way counter-clockwise and RF gain all the way clockwise, I don't have anything, no static, nothing.
When I key the mike, it makes the slightest KRHHH noise when first keyed.
With the wife sitting in the same driveway, in two different trucks with working radios, she cannot hear anything when I try to "send"
I hear nothing when she tries to talk to me.

One of the other trucks has an identical radio that was bought at the same time, same Cobra speaker, and etc. and it is working fine.

From my description, what possible causes come to mind ?

Thanks for reading.
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Old 10-19-2017, 02:20 AM
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Okay; update on the situation:

I did learn one surprising thing during this episode: the weather comes in loud and clear even when the antenna is disconnected; that with the nearest transmitter being about 90-mile away.

I swapped mikes to no avail.

I removed the non-working radio and swapped in the identical radio from the other truck, connected all the speakers, coax, and power; I flipped it ON and it instantly began receiving; asked for a radio check and got a response.

I connected the non-working radio in the other truck and got nothing.

With the good radio in place of the dead radio, everything was fine UNTIL I closed the truck door and lost it all.

I then wiggled the antenna and got it back for a second; I wiggled the coax just inside the door and got it back for a minute or so; I opened the door and it went to working again.

I then disconnected both ends of the coax and alligator-clipped a continuity meter to the coax ground connections and had a good solid circuit; but, when I checked the center pins, I got no continuity; I could wiggle and flex the coax and get intermittent continuity.

So, I got a brand-new Fire-Stick big fat "trucker" coax that I had on hand and temporarily connected it; everything worked perfectly.


Thus, my diagnosis of what has occurred is:
Where the coax comes through the door, NOT just draped through the door jamb but actually through the door, has just enough slack to open and close the door, and then heads up the windshield pillar, the last three years of opening and closing the door, thus unfolding and refolding the coax each time, has caused the internal circuit of the coax to break.

Me not being aware of this situation, I grabbed the mike and said something to another driver, maybe more than once; the coax being internally separated is equivalent to keying the mike without an antenna; thus, I most likely have fried whatever fries in such situations; blown a final or whatever.

I really like this radio, Cobra 29 WX NW ST, and would really like to have it fixed.

From my description, does it read like a blown final?

Does anyone know if the Mosfet thingamajiggy for a Cobra 29LTD Classic will work in my radio ?

Thanks for reading.
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Old 10-19-2017, 05:07 AM
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Transmitting into a non load, ie antenna disconnected or open/shorted coax is a very good way to blow a final on any kind of transmitter.

On reading your original post it does sound like a bad coax for both send and receive.

No idea about your Mosfet question.
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