Question about Cobra 25 LTD 40-Channels Base CB Radio

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Have an intermittent problem transmitting on my cobra 25 nw ltd, comes and goes, have used several mics and problem still persists, I think it is internal, where do I begin to look internally? Is there a common component that goes bad and needs to be replaced, or maybe a touch up solder job?

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Posted on Jan 02, 2017

  • 328 Answers

SOURCE: cobra 25 ltd wx classic

the mics on these cobras have a receive wire in them so the transmit will still work even if the receive wire is broken,if this wire is broken the unit will not make any sound...........remove the plug from the radio end of the mic and check the connections on the 5 pin connector.....(could be a cold solder or broken wire) or try a new mic or one that is proven work on another radio
hope this helps.................good luck!

Posted on Dec 25, 2008

  • 200 Answers

SOURCE: cobra 29 nw ltd won't transmit

Have you cracked the radio open yet?  check for loose connections etc.  get back to me if that doesnt yeild any results

Posted on Jan 22, 2009

  • 39 Answers

SOURCE: NEED HELP WITH MIC WIRING FOR COBRA 25 LTD ST

1 Shield 2 White 3 Red 4 Black if the radio keys up as soon as you turn it on reverse 3 and 4 I am not familiar with that mic.But the way I actually should have given you the wiring order is as follows:1Shield 2 Modulation 3 and 4 key up I hope this helps.

Posted on Feb 20, 2009

  • 773 Answers

SOURCE: cobra 25 LTD classic no transmit or receive.I have

With the radio on, and the case off. Rub your finger gently across the contacts of the audio chip on the trace side of the board. If you hear noise from the speaker it is good. if you don't hear anything(make sure the speaker is hooked up) then the audio chip is bad. You need to change it.

Posted on Jan 28, 2010

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SOURCE: 29 cobra ltd c.b. wont transmit or receive

make sure the RF gain is all the way up, and the dynamic is all the way up or most of the way up.

When you say the antenna is good, have you checked the SWR's and or have tuned the antenna to be the correct length for the radio? If this has not been done ever, your radio could be a brick.

Also, make sure the PA/CB switch is on CB. if its on PA(public address) it will not receive or transmit because it is on PA mode, which if you have one hooked up, a PA speaker, then you can talk to people through it out side your car.

Also, make sure the S/RF SWR CAL switch, its the first one on the left, is all the way up on S/RF. this is your signal/ receive setting for the meter. When you hold the key, does this needle swing forward? As well does the RX/TX light turn red? If it does, then the radio is transmitting.

There is another light on the radio under the TX/RX light. It is the Antenna warning light. If this light comes on when you transmit, or has come on all the time during transmit, and now it doesn't then the radio is a brick. That is a warning light. It means that the antenna is not matched, or has not been tuned to the radio. If this has not been done ever, you have killed the radio.

Here is why. When you transmit, you are sending off a radio wave. This radio wave, at 27mhz, is about 36 feet long. In order for the wave to radiate off the antenna, the length of the antenna has to match the length of the radio wave. Now it does not have to be a full 36 feet. It can be an exact multiple of 36 feet. In other words it can be 1/4( one quarter) or 5/8(five eights) of a wave in length. 1/4 of a wave is 108 inches, or 9 feet long. Your antenna is still probably does not seem 9 feet long, but there is usually a loading coil that is not exposed making up the rest of the length of antenna, so that it matches the length of the radio waves electrically. If you were to stretch the coil out with the antenna whip, it would be 9 feet long.

When the antenna does not match the wave length, part of the RF energy does not leave the antenna, and goes back down the feed line(coax) and hits the transmit transistor. Prolonged reflection to the transmit transistor, otherwise known as the final will blow it out. As well depending on how bad the length was off, the more off, the more reflect energy, the more RF energy you are blasting back into the radio, and this causes more things then just the transmit to blow out. Some time the receive goes along with it when it finally goes.

So if the RF gain is up all the way, which by the way is basically how much receive you have, and there really is no reason to have it down at all, and the CB/PA switch is on CB and the needle does not swing forward when its on the S/RF setting, chances are that the radio is now no good.

It is fixable, but if there are no CB shops near you then you will have to send it out. And Cobra will not cover this under warranty because its stated in their warranty that they do not cover damage due to high SWR.

Posted on Apr 06, 2010

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I have a cobra 25 nw st and it will not transmit


Hi, my name is John. Welcome to FixYa. Turn your MIC GAIN or DYNAMIC to MAX. Try another mic on it , if that does not do the job, let me know I will have further. Thanks for choosing FixYa. good luck John

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Hi,my name is John. Try turning your MIC GAIN to MAX. Let me know how it goes. Could be something internal that I might could help you with...Hope this was helpful...Rate this solution on the four thumbs-up ...Good luck.... John

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If the receive works ok,sounds like a mic
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What happens if you "key up" and "let off" and the transmitter "hangs", you remove the microphone plug from the Cobra ?
Will it still be transmitting or will it stop ?
If it stops, the problem is in the microphone with a "hanging" switch which you can easily clean or replace.
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1 Answer

Cobra 29 nw ltd won't transmit


Have you cracked the radio open yet?  check for loose connections etc.  get back to me if that doesnt yeild any results

Dec 23, 2008 | Cobra 29 LTD CB Radio

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Cobra 25 ltd wx classic


the mics on these cobras have a receive wire in them so the transmit will still work even if the receive wire is broken,if this wire is broken the unit will not make any sound...........remove the plug from the radio end of the mic and check the connections on the 5 pin connector.....(could be a cold solder or broken wire) or try a new mic or one that is proven work on another radio
hope this helps.................good luck!

Dec 18, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

1 Answer

I have a cobra 29 and all it will do is light up. It will not receive nor will it transmit. What might be the problem?


the easiest thing to check first is the mic..........if the mic is broken cobras wont receive or transmit
hope this helps.......good luck!

Dec 05, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

1 Answer

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Hello Darren, Yes it sounds like the mic is wired bass ackwards,,! A cobra 25 mic wiring is
PIN #1- Shield or ground wire
PIN#2- Audio or Transmit modulation
PIN #3- Transmit or Dead Key
PIN #4- Receive Audio.
When your keying the mic, the RX wires are being connected to make the RX work,,,
*** Let me know how you get along with it. Either buy a new mic wired for your radio or you or someone comfortable with soldering needs to resolder the correct wires back on the mic plug,,,Like I said, let me know and have a great day,, Mechanic is back quiet!

Oct 21, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

1 Answer

Cobra 29 NW LTD CLASSIC NIGHTWATCH


Dear RobertTx,

Sounds like you may have a leaky or shorted capacitor somewhere in the power circuits, or a defective transistor in the same circuits since it affects both the transmitter and receiver.
Common problems with receive and transmit intermittance can also be the antenna or its connections. The fact that it goes away if the radio is turned off, then on again after a short time points to something common in the power supply section. Unless you have test equipment and a working knowledge of electronics it will be difficult for you to troubleshoot on your own.

Jules

Oct 21, 2008 | Cobra 29 WX NW ST 40-Channels Base CB...

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