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Cobra 29ltd classic : no rx / tx

Radio was plugged in backwards , with 3 amp fuse inline . I replaced d23 , and fuse ,brought it back to life .I tried several ( known good ) mics .Still no rx / tx .
Altho the rx / tx light does switch back and forth showing rx / tx

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  • ejramsey Feb 05, 2008

    Thanks for advice , I will let you know how it turns out .

    Thank You

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  • Master
  • 6,966 Answers

Hi,

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.

Posted on Feb 04, 2008

  • Radio-tech155 Nov 12, 2015

    not all had a ta7222ap for an audio chip. they switched to a TDA2003 ..

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1 Answer

What size fuse is used in COBRA 29LTD CLASSIC radio.


First question should be, what happened to the last one? If the fuse blew on you, you need to find out why. If it was just missing when you got the radio...

That said it is surprising that the manual doesn't state this value directly. However, it is a 4W transmitter and the manual I referenced states that you should connect to an "accessory" fuse for mobile installation. My car has a 10a fuse in that position but a 3A slo-blow in the power wire's inline fuse holder should do the trick. (The main reason for using the "Accessory" fuse is for operation with the engine off, but not battery drain unless the key is inserted.) Another clue for my SWAG is that for a "base station" installation, the manual recommends a 12Vdc power supply that can deliver >2A... So I think we are in the ballpark.

If you have lost your original manual you can get a replacement from the Cobra support site here:
https://www.cobra.com/support/product-manuals

V/R,
Veg

If a train station is where the train stops, what happens at my workstation?
~Author Unknown

May 04, 2016 | Radio Communications

1 Answer

Cobra 29LTD Classic RX seems to go off frequency. Transmit is fine, but can't receive on same channel. i.e. TX on Ch 11, but RX some other frequency. Was talking to my wife and suddenly, her signal was...


all functions of the radio are performed by the main IC 2816c . The frequency is controlled by this also and if it is blown you will loose your frequency and the problem that emits is in your statement.

Oct 23, 2011 | Cobra 29 LTD CB Radio

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

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

2 Answers

Does the rx/tx green light stay on all the time? Cobra 29LTD


Yes the light will stay on and change when you key the mic

May 07, 2010 | Cobra 29 LTD CB Radio

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
CBTricks.com

TIPS:
You need to have Acrobat Reader version 5 or newer installed to view the files with pdf_1.gif icon.
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.
25ltd_st_sm.jpg
Click Picture to See Close-up
cobra_29ltd_st_29wx_st_side.gif 29LTD ST Owners Manual pdf_1.gif
29WX ST Owners Manual pdf_1.gif
DIAGRAMS
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
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
Stock
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
Sadelta
1- Shield
2- White
3- Brown
4- Green
Turner
1- Shield & Red
2- White
3- Blue
4- Black
Yellow NC

Nov 17, 2009 | Cobra 29 LTD CB Radio

1 Answer

Have cobra 29 nw ltd keeps blowing fuses inline and in cigarette lighter adapter adapter is 10 amps and inline is no more than 5 amps


This is an easy fix if you are comfortable soldering.

You must have hooked it up backwards. Big problem when using a cigarette lighter adapter. You have to be careful, if you hook a radio up backwards you blow the polarity protection diode.

  • Go to radio shack and buy an N1004 diode.
  • Open the radio
  • Look towards the back right of the radio for a black diode D23. it will probably look burnt, but not always.
  • Use a soldering wick to remove the solder holding the diode in.
  • Remove it, and replace the diode making sure its going in the same direction as the old on. Strip on the side the triangle is pointing.
  • Solder it in.
  • Test the radio
That should do it.

Make sure you are careful to hook the radio up to power corrctly.

Nov 14, 2009 | Cobra 29 LTD CB Radio

1 Answer

Blowing fuse


Your polarity protection diode has been blown. If you tried hooking up your CB and accidentally pushed the plug in backwards. Inside the radio, there are 2 big black diodes near the transformers, D8 and D23. Replace these with the same or bigger. You can the burnt one out and the radio will work, but if you hook it up wrong again, it will fry the radio.

May 02, 2009 | Cobra 29 WX NW ST 40-Channels Base CB...

1 Answer

Fuse


Hi,

There are only a couple of components that could cause the fuse to blow. They are:
1. Reverse protection diode (D23)
2. filter capacitor (C123)
3. Outputs (TR14 & 15)
4. Audio Amp (IC4)
5. Zener Diodes (D22 & 19)
6. the fuse itself (it should be 2 Amps

Hope this be of 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.

Feb 12, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

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