Cobra Classic receive problems???

Hiya.
Your problem sounds way bizarre, complete with non sequiturs. The model number, you mentioned it's a "cobra classic" -- is it a "29 Classic"? Anyway, the Calibrate knob has nothing to do with reception; it's just used in one of the steps for checking the tuning of an antenna. I think the best clues you gave are that an external speaker didn't help, and that the lights dim somewhat when you're receiving signals. It's likely that wherever you're picking up your 12 volts and/or ground (for the red and black power leads) are insufficient for the demands of the radio, so that when the radio tries to "play" sounds through the speaker, the voltage is dipping down to the point where the amplifier can't work right. The lamps dimming is an indication of that happening.
Where are you getting your power and ground now? Try this: unplug the antenna from the radio. If the radio shuts off, it means the only ground the radio had was from the coax shield, which isn't enough.
Ideally we recommend people get both power & ground ("red & black") directly from the battery avoid voltage drop and noise.
Plus it's easier than replacing the radio and having the same problem.

 

It's possible that the connection to the posts on the bottom(s) is/are bad, or the other end of the leads that supply them are shot. If you've got an accurate voltmeter, like an digital DC voltmeter, try putting it across the posts with the radio off, then see if the voltage drops at all when you turn the radio on, and especially when you either turn the volume up, squelch down, and RF gain up (so it will make the most noise), and for most electrical draw, hit the transmit switch on the microphone and see what happens to the DC voltage on the supply posts.
Even without the meter, though, it'll be interesting to see if the radio dies without the antenna lead being hooked up. That'll let you know that the ground post's wiring to the dash is apparently t.u.
Let us know what'cha find.

 

If the lights dim on the cb when you key it, it is an issue with the antenna. I would suggest you run a dedicated coax from the antenna to the cb, preferably 18 ft. Do not coil the excess cable, instead stretch it out lengthwise behind the radio.

When I setup mine, the lights would dim and I'd get the antenna warning light. Reworked the coax and my issues went away.

 

Probably a short in the radio itself or the power source. I would suggest testing a different CB radio in its place if you have a spare.

 

I'm gonna give a partial "thumbs-up" to Hatless's diagnosis/prognosis on this one. If you ignore the part about needing an 18-foot piece of coax, and the coax's shape contributing to what the lights are doing, I'll go along with the idea that since the radio seems to transmit OK, then there's something wrong with just the receiver in the radio.
I understand the radio came through Amazon. I also realize that Amazon sometimes sources items that are used, as well as new (well, at least as far as books, CDs, DVDs, etc.)
Is there any chance you can come up with another radio to test with, as Hatless suggested, using the existing antenna and DC connections, to see if the problem follows the radio or the installation? I understand the problem is intermittent, but it'd be great if you can somehow precipitate the conditions by activating different accessories, like fans, wipers, an inverter -- basically any other driver-accessible device that uses battery power that *might* be getting its power from the same source as those power posts on the dash.
Or, just cuz it's a better practice in general, go ahead and run some 14- or 16-gauge automotive zipcord right to the battery, so you can bypass all the myriad connections that may exist between the battery now and the stock connectors on the dash. Remember to put a big fuse right next to the battery on the positive lead in case there's a dead short someplace along its run to the radio, and the "proper" fuse (probably 3 amps or so) next to the radio to protect the radio in case something inside it shorts.

That will let you eliminate an "iffy" truck wiring harness as the source of the problem -- it may actually be that during the same times that your receive sucks, so does your transmit, but you're not able to evaluate it because you can hear the answers to requested radio checks.

That radio is so ubiquitous that nearly any other driver ought to have a mount and harness that will plug directly into it. Ask around next time you're at the yard or a TS or someplace, ask if you can try plugging your radio into their rig, see how it sounds, take note of if it seems to foul up when everything else *except* the radio is different. If it's someone you trust (or who trusts you LOL) maybe you can actually swap radios, see if the problem follows the truck or the radio.

Lotsa ways to narrow down the source of the problem, but for the time being there are many variables. Divide and conquer.
73,
Handlebar

 

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