Question about Cobra 18 WX ST 40-Channels Base CB Radio

2 Answers

Cobra 18 wx st receives-wont transmit

When i key up the tx lites wont come on and i have no audio output.
i have checked-mic-antenna-coax. the problem is inside of radio,what do i need to check? i have ohm meters an modulation-swr-power meters

Posted by wwwbb528 on

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2 Answers

JOHN BABA

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Take the cover off, flip it over solder side up, check all solder joints for cracks, cold solder joints, check the safety diode where it comes in the radio, before I go further, can you pick up the weather channel?...Does the PA work?...need to check the pre-driver and finals,audio chip, hook up the power meter using a coax three foot jumper from the output from radio to the input of the watt meter, then the antenna, first check the SWR, on the scale on the meter to cal/swr mode,adjust it to spec, then while still keyed down turn the dial to SWR,if it is the safe range your ok,then turn the Dial to 10 or 20 watt scale and key the mic. Does it have any wattage? If not suspect the finals, they are located on the back rail, if it does have RF then its the audio chip, its located on the right side rail facing you,closest to you.remove it and replace it with same ....hope this helps....

Posted on May 21, 2010

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Anonymous

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I have a Cobra 18 wx st. I am not able to transmit anything on it. I have checked the antenna cables and and all external connections. I receive all the wb just fine but the CB gives me nothing. I tried a different mic and got the same result except when I turn the squelch all the way down and a little above its makes a weird noise. When i press the call button with both mics the TX and the RX lights come on but the power bar shows nothing. Any ideas?

Posted on Jul 06, 2010

  • Matt Young Nov 28, 2011

    i have the same problem, any help would be much appreciated!

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That's usually a defective amc stage that produces RX audio and TX modulation. It's an integrated circuit that will require a tech fixing it. You will have a transmitted carrier with no modulation, and no sound in your speaker. However, make sure you have a good mike plugged in first, and substitute a known good mike to verify it's not the mike. With the WX band working, the above may not apply.

See if you have a carrier...signal going out, but no modulation. Get your Tech to check the mike wiring/circuitry inside the radio, also.

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Hi rem_fishing ,

Would seem that your Audio IC is busted. No receive audio, no TX audio. This would be IC2, KIA7217AP

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Hi,

Your post of 2 lights; 1 is to indicate that you are transmitting when keying the mic is normal. The 2nd indicating an antenna warning (or SWR) should be corrected. You are right in starting with the coaxial cable which of course would include the PL259 connector. Verify that there are no breaks, over-bended loop, exposed ground/shield and that the solder of the center wire as well as the braided shield/ground is in order.

If it is a mobile setup, further verify that the antenna mount (except when magnetic) is properly grounded to the body of the vehicle and free from rust/corrosion. In some instances, it is the antenna itself that need checking or even possibly replacement.

Alternately, if the needle doesn't swing to the right side of the meter when the mic is keyed, it is possible that your finals (2SC1306) needs replacement.

Hope this be of some help/idea. Pls post back how things turned out or should you need additional information.

Good luck and kind regards.

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