Cobra 29 LTD CB Radio Logo

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Joseph Midjette Sr
Joseph Midjette Sr Posted on Feb 01, 2014
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Where can I find a new replacement modulation transformer for a cobra 29 ltd classic?

I have dead key, Rx works, TR17 tests good, New Tx final fixed no dead key, still have no modulation, mic tests good, used buzit on pin 4 of audio chip and get noise through speaker until I key the mic. Think I need a modulation transformer. Unless someone knows something else I'm missing to check. Also, how do I test the modulation transformer to be sure it is the culprit?

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Cheap CB Radio Equipment, Check It Out https://cbradioequipment.com

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If you are thinking about replacing the transformer you can either get one through Cobra or remove one from another radio.

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Simple,just chech the input resistance and out put...they should have even small resistance always example .5ohms .3 ohms it counts...

  • Joseph Midjette Sr Feb 01, 2014

    input and output resistance on what?

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4 Related Answers

Tumbleweed01

  • 1 Answer
  • Posted on Mar 16, 2008

SOURCE: 29 help

hi, sounds like you have a problem with the SWR' S Probably too high. Tumbleweed01

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Anonymous

  • 200 Answers
  • Posted on Jan 22, 2009

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

Ernest Taylor

  • 67 Answers
  • Posted on Feb 27, 2011

SOURCE: cobra 29, no rx, no tx, pa dose not work, good

Not sure which model you have as there are at least 13 cobra 29's. I am using the LTD as an example. You say good mic? Is it made for this model? If it is good then I would have to say the final audio stage is not working. The TA72222AP is the IC that is the final audio amplifier. Check pin 1 of the TA72222AP ic for 12 volts. If 12 volts is present then replace the audio IC TA72222AP. If 12 volts is not present then you have power supply problems that are internal. The conclusion I have made is based on no rx audio, ( could have been the jack at the pa and ext spkr) but you say they don't work either, also no meter movement during modulation check (that does not need a spkr to make the meter move) so yes I'm 99.99% sure its the final audio stage is a bad. If your model is not the LTD then the IC could be different but still the same audio final is bad. Replace the part which should be fairly inexpensive. If it uses a metal heat sink be sure to apply heat sink grease when installing new part.

Laron71

Laron

  • 146 Answers
  • Posted on Jul 02, 2011

SOURCE: Cobra 29 ltd Classic no

Check speaker and plug external one in if you have it.

swap mic could be a broke wire or bad switch in handset.

check antenna and coax connections.

i know checks sound basic but they could save you a lot of headaches later

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0helpful
2answers

Cobra 29 ltd Classic no sound, no rx, all lights work rx,tx, lite up. The SWR meter moves when mic is keyed up.
Check speaker and plug external one in if you have it.

swap mic could be a broke wire or bad switch in handset.

check antenna and coax connections.

i know checks sound basic but they could save you a lot of headaches later
Read full answer
May 31, 2011 • Cobra 29 LTD CB Radio
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Cobra 29, no rx, no tx, pa dose not work, good mic, good ext. speaker, mic. gain all the way up, and you can see meter in face neddle moveing it rec. just no audio at alland no modulation.
Not sure which model you have as there are at least 13 cobra 29's. I am using the LTD as an example. You say good mic? Is it made for this model? If it is good then I would have to say the final audio stage is not working. The TA72222AP is the IC that is the final audio amplifier. Check pin 1 of the TA72222AP ic for 12 volts. If 12 volts is present then replace the audio IC TA72222AP. If 12 volts is not present then you have power supply problems that are internal. The conclusion I have made is based on no rx audio, ( could have been the jack at the pa and ext spkr) but you say they don't work either, also no meter movement during modulation check (that does not need a spkr to make the meter move) so yes I'm 99.99% sure its the final audio stage is a bad. If your model is not the LTD then the IC could be different but still the same audio final is bad. Replace the part which should be fairly inexpensive. If it uses a metal heat sink be sure to apply heat sink grease when installing new part.
Read full answer
Feb 26, 2011 • Cobra 29 LTD CB Radio
0helpful
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Cobra 29 has good dead key but no mod.and no rx
probable took out the keying transistor. If you want it fixed give me a shout. Dodgem250.com
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Apr 09, 2010 • Cobra 29 LTD CB Radio
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Red RX/TX and red ANT light on my CB
Well,first hand ,some cobra radio,s have red some have green RX/TX lights, but are you modulating? Some green lights turn red. What is your standing Wave on the antenna,s? You need to check it and the output of the radio. To do this you need a watt or field strenth meter. Can get one at Radio Shack. Your standing Wave is ok as long as it is below a 2. That has to be done on the antenna. ..hope this helps...
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Mar 11, 2010 • Cobra 29 LTD CB Radio
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MY COBRA 29 LTD CLASSIC WILL NOT TX BUT RX VERY WELL. CAN'T SEEM TO CALIBRATE CORRECTLY.
Hi and welcome to FixYa,

Initially, check the final and driver, TR14 and TR15 using a transistor tester or ohmmeter..

Postback results.

Good luck and thank you for asking FixYa.
Read full answer
Oct 30, 2009 • Cobra 29 LTD CB Radio
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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
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Dec 23, 2008 • Cobra 29 LTD CB Radio
0helpful
1answer

No receive cobra 29 ltd classic
Hi and welcome to FixYa,

Initially, pls confirm that there is modulation (transmit audio). The reason I asked is if IC4 (TA7222P) is blown, then the radio would have no audio amplifier which would explain no receive audio. Additionally, the final and pre-final (TR15 & 15) gets is modulated TX+12 through D8 from T1 which in turn is the output of IC4 through C48.

Perhaps a schematic diagram may be of further help.

Good luck and Thank you for using FixYa. Happy Holidays.
Read full answer
Dec 18, 2008 • Cobra 29 LTD CB Radio
17helpful
2answers

Cobra 29 Ltd Classic
In most cases just turning up VR4 is more then enough. Replacing the final, tr14 with another transistor requires changing many more parts to get it to work.

With a new 29, there is no need to change the final. Just turn vr4 all the way up and you will see around 20 - 25 watts. L13 won't gain you a single watt. L12 will raise the dead key, and usually you want a lower dead key for good swing. L14 will gain you a few watts, but don't adjust this unless you have a watt meter. You turn it out to increase wattage, but too much will over bias the final and shorten its life.

You hook it to a watt meter with a dummy load. Then say a steady AHHHH into the mic while keyed. Turn the slug out until the needle stops going up, then back it down to where it stopped.

The easy thing to do, and you will be pleased is just to turn VR4 up. Now, Up is counter clockwise. Its a variable resistor, so the less resistance, the more modulation. So you want to turn the VR down.

that will be more then enough.
Read full answer
Sep 06, 2008 • Cobra 29 LTD CB Radio
0helpful
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Codra 29 nw ltd classic
For the money,the Cobra 29 nw/st is just as good if not better than a Galaxy. Cobra is more durable by far. I have had 3 of these cobra's in the last 30 years. Only had to replace the last one because the tractor got hit by lightning.
Sure would not pay big money for a name.
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Mar 19, 2008 • Cobra 29 WX NW ST 40-Channels Base CB...
1helpful
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29 help
hi, sounds like you have a problem with the SWR' S Probably too high. Tumbleweed01
Read full answer
Mar 12, 2008 • Cobra 29 WX NW ST 40-Channels Base CB...
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Cobra 29 ltd Classic no sound, no rx, all lights work rx,tx, lite up. The SWR meter moves when mic is keyed up.

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