Question about Cobra 29 LTD CB Radio

1 Answer

No audio i've cobra 29ltd with no sound symptom.tx works fine,but rx is dead(no sound)mike was checked ok.board was checked for cold solder, touching components and loose wires.resoldered audio ic and still nothing. when plugged very small speaker to ext.speaker plug there was very faint sound of "talk",but with gain ot the max.running out of ideas.please help.

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  • falcon2000 Sep 07, 2007

    i think you're right,however i don't have a schematic and p/n is scratched off.if you know the p/n that will be helpful.thanks in advence.

  • falcon2000 Sep 07, 2007

    i think this will be the case,however i don't have a schematics and p/n on ic is wiped off.if you know what it is,this will be helpful.thanks in advance

  • falcon2000 Sep 07, 2007

    thank you.i'll try to get it(service manual).
    thanks again,you have been very helpful.

  • falcon2000 Sep 07, 2007

    ok.i've solved the problem.i got hold of schematics for this radio and defective ic was TA7222AP (audio ic)however even after replacement there was still no ic was verified to be defective,but i've also noticed J201 mic-socket's one of the pins #4 was deformed,so there was no connection.after reforming it to proper shape audio returned closed.if anyone is interested,i can e-mail the schematics for cobra 29 ltd is in .pdf form.
    thank you

  • lordgomer Feb 19, 2008

    i have a cobra 29 ltd classic and it was working fine. one day it worked and later on that evening it would not do nothing. it has talk back and that works through the speaker but no other noise is aparent. i hooked it up to a nother setup with a ext. speaker and still nothing im at a lose for what could have happened. any ideas?



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Have you tried to check the audio as it is coming off of the detector right before it enters the first audio amplifier? you can check this with an oscilloscope and then trace the signal through the stages of amplification the signal should get bigger. I think that you may have blown the final audio output amp. and what you are gearing is pre-driver audio through a leakage path. This is just a hypothesis, but I have seen this happen before.

Posted on Sep 06, 2007

  • 1 more comment 
  • Henry McKelvey
    Henry McKelvey Sep 07, 2007

    Hello falcon2000,

    I'll try to look up the data on this device to see if I can find a schematic for you. It's a long shot but who knows.

    Thank you,


  • Henry McKelvey
    Henry McKelvey Sep 07, 2007

    They have one on Ebay:

  • Henry McKelvey
    Henry McKelvey Sep 07, 2007

    This service doc has every thing it looks like, to at least locate the items in your CB.



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1 Answer

I have a none amplified D104 G stand it came off my TRAM D201 IT has a two center leeds that's shielded I know this will work on my cobra 29LTD but I don't get it please help

First, you have to replace the cable as you will need a minimum of 4 wires, 2 of them for the transmit and receive switching, and a shielded cable for the audio. It would be nice to have another as the common for the TX/RX switching but the shield is commonly used for this.

You will need to re-wire the switch in the candlestick to allow switching from RX to TX.

Google "D104 to cobra 29 mic wiring" and you will find many hits for this.
Your microphone was not intended to work with this style of radio. To save a buck, the CB manufacturers removed a 50 cent relay to do the transmit/receive switching. You can see what happens when you remove the microphone when you are listening to the Cobra. It'll stop producing any sound. This won't happen with the Tram,

Also, you may have problems with the microphone as it is high impedance as indicated by no transformer or preamp in the base of the microphone. This may be a problem as the Cobra has a relatively low impedance input.

Aug 07, 2016 | Cobra Radio Communications

1 Answer

I have expanded my 25 ltd and want a rx/tx fine tune possibly using the rf gain control?

look at a schematic of a 29ltd to do that.. the 25 does'nt have it in there easily.. the 29 can be fixed to change tx/rx freq. with the delta tune

Feb 11, 2011 | Cobra 25 LTD 40-Channels Base CB Radio

2 Answers

My cb cobra 29 ltd problem is channel 1 is ok but channel 2 not receive

Did you have someone get on channel 2 to see??? Maybe channel 2 was quiet and channel one had better receive or noise.. You never know until you check it with another radio. That is NOT a common issue at all on those radios. Better off doing that test.

Dec 28, 2010 | Cobra 29 LTD CB Radio

1 Answer

I have a Cobra 29LTD serial number 43011339 that has no TX or RX. The radio powers up but the RX led is not on. TR 23, R105 and TR 21 get hot to the touch as soon as the radio is powered up. I replaced...

Hi,my name is John. you need to adjust both TR23 & TR21 to 8 volts.......then you should be OK.......good luck. Rate this solution on the four thumbs--up.thanks John.

Oct 07, 2010 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29ltd CLassic, TX power and audio is ok, volume from spkr is good, squelch works but no cb recieve.

Try a new Mic. Make sure its a working mic. If you have a bad mic, the receive will not work.

Aug 22, 2010 | Cobra 29 LTD CB Radio

1 Answer


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.

Jul 30, 2010 | Radio Communications

1 Answer

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...

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.

Jul 06, 2010 | Cobra 18 WX ST 40-Channels Base CB Radio

1 Answer

I have a cobra 148gtl with 5 pin side plug for mic.Im trying to wire a superstar dm 1000 echo mic to it,red,yellow,blue,white,& unsheilded wires dont know were they go.???????

ALLways start with ground. Find ground on radio pin with ohm meter. EVERY thing operates off ground. Once you find ground on radio....solder your ground wire on mike cord to corresponding # on mike jack. Once you have ground on proper pin then all else is elementary......use ohm meter to see which wires are TX and RX on mike.....last wire is audio wire.

Jan 20, 2010 | Cobra Radio Communications

1 Answer

I have a Cobra 21- 23 channel CB and the wires pulled out of the plug. The mike wire has red,yellow black,blue,whiteand a ground. My plug has only four prongs to solder to. What four colors do I use?

Hello there
Here is the diagram for you
Cobra 29LTD, 29LTD ST, 29WX ST
Documentation Project

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If the files with jpg.gif or gif.gif icon will not display see the Site FAQ for help on printing, viewing and using this information.
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cobra_29ltd_st_29wx_st_side.gif 29LTD ST Owners Manual pdf_1.gif
29WX ST Owners Manual pdf_1.gif
29LTD ST Schematic Diagram pdf_1.gif
29LTD ST Schematic Diagram gif.gif
29WX ST Schematic Diagram pdf_1.gif
WX Schematic Diagram pdf_1.gif
29LTD, 29LTD ST, 29WX ST Factory Service Manual pdf_1.gif
Page 1 to 11
Page 12 to 34
29LTD Factory Service Manual pdf_1.gif
29LTD Schematic Diagram pdf_1.gif
29LTD Schematic Diagram jpg.gif
29 LTD Classic Schematic Diagram pdf_1.gif(Courtesy of Rick Jackson)

Mic Wiring
1- Shield
2- Audio
3- Transmit
4- Receive
Astatic (4 wire)
1- Shield
2- White
3- Red
4- Black

Astatic (6 wire)
1- Shield & Blue
2- White
3- Red
4- Black
Yellow NC
Daiwa EM-500
Cobra CA Series

1- Shield & Black
2- Red
3- White
4- Blue
Galaxy DC-521S (4 wire)
1- Shield
2- Yellow
3- Red
4- Black
Galaxy CB-660EI
1- Shield & Black
2- White
3- Red
4- Blue
1- Shield
2- White
3- Brown
4- Green
1- Shield & Red
2- White
3- Blue
4- Black
Yellow NC

Nov 17, 2009 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29ltd classic : no rx / tx


D23 is the reverse protection diode and it shorting is the primary reason your fuse blew. As you posted, power was applied in reverse, hence other components would also fail. Pls check:
1. D22 - 9.1V Zener Diode
2. TR23 (2SC1096) 9 Volts regulator
3. D19 - 5.1 Zener Diode
4. IC4 (TA7222) - Audio Amp
5. TR14 (2SC2029B/10) - Finals
6. TR15 (2SC2028B/20) - Driver
7. Most capacitors over 220uF (like C123, C114 & C112)

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

Good luck and kind regards.

Feb 04, 2008 | Radio Communications

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