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My cobra 25 ltd classic.. transmits with a hummmm .. they can hear the voice .. but the noise comes with it .. any ideas.. i am using this radio in my truck,, so there is no power supply involved...

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  • Radio Commun... Master
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Have you tried changing your mic/ It could also be from your mic connector to the pcb or it could be a electrolytic cap that's leaking.Try the easiest way first then go for the caps on the inside.

Posted on Nov 04, 2013


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Posted on Jan 02, 2017

  • 68 Answers

SOURCE: Cobra 29 LTD Classic Operations Manual

For the operation manual, go to or:


Posted on May 10, 2008

  • 6966 Answers

SOURCE: Cobra 29 Ltd


Appreciate the direct "Ask Me" again.

The initial posting would still hold true, best would be:

  • remove TR18;
  • replace 2SC2069 with 2SC1969; and
  • adjust L12, 13 & 14.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards. Thank you for using FixYa.

Posted on Sep 08, 2008

  • 13 Answers

SOURCE: I went to adjust the V4 pot on my Cobra 29 LTD

Let's see you wanted more modulation, so you twisted the VR4 pot so hard that it broke off . First, if the radio has been clipped, VR4 is not in use . FYI, I think that full Counter Clockwise is wide open . VR4 is a 680 ohm pot, but can read to 800 ohm . Most folks defeat the AMC circuit by removing D11, C73 will do the same . You may actually be better off by leaving the circuit intact, and changing C71 from a 220uf 10v to a 33uf - 47uf at 16v, or 25v, to 50v . This will make the AMC transistor react faster for cleaner operation . Set VR4 so that it just prevents severe over-modulation . If you want modulation that bad, change C42 to a 3300uf 16v - 25v . That will increase available power for your audio amp . Make sure that R48 is 220K Ohm . For swing, remove Jumper JP36, and install a 18 ohm to 100 ohm 1 watt resistor(higher number = lower dead key) in parallel with a 47uf to 100uf 50v cap . I use axial caps, if you can find them, and piggyback the resistor . Outherwise, it can be mounted on the botton of the board . Make certain that the negative lead of the cap is in the rear hole . Without an amp, I use 18 ohm, and 47uf at 50v . I also add a "short" jumper on the bottom of the board from the audio transformer base ground to the center grounded area of the board to prevent feed back . You just have to jump a few small traces . The center area is grounded, follow skinny the traces . The jumper just beefs up the ground . Well, I hope that satisfies your lust for modulation ! J

Posted on Nov 28, 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

  • 1851 Answers

SOURCE: 29 ltd classic wont transmit

Great radio when it works.
If you have your settings on CB - not PA - -be sure that your Cobra has that setting selected.
If CB -is selected and still nothing - be sure you have a working mic. These wires are fragile and can break internally. One easy way to check is to borrow a cobra mic or even drop by a CB repair shop and ask them to do a mic check with the mic - it is free.

If you have a bad mic replace it and all should be well.
If your mic is good and it still doesn't transmit you will need to replace the finals in the unit. It is common that these burn out of you got too close to someone with too powerful a radio. The CB shop will need to look at it further and repairs should not be over about 40.00.

Good luck with your Cobra.

Posted on Mar 31, 2010

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1 Answer

I have a cobra 25 ltd classic change final to 1969 now I can hear but no transmit. Final is new ......where should I look next?

Was the radio working before the high power transitor mod?
If so, it appears there is more to do than just replacing the transistor.
Check under" cobra 29 high power mod with 2sc1969 transitor." There are instructions for the complete mod.
Hope this helps


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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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