Question about Cobra 29 LTD CB Radio

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Cobra 29 ltd. turned rv4 switch and cb started smoking. what is the cause of this

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  • Cobra Master
  • 1,795 Answers

If this is a used radio its because some golden screwdriver got into it but if its a new one then its the radio.Check the reverse polarity diode in either case to see if its burnt. If so replace it and see if it happens again.

Posted on Sep 01, 2014

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Posted on Jan 02, 2017

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Dodgem250
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SOURCE: Cobra 29 LTD Classic Operations Manual

For the operation manual, go to cobraelec.com or:

http://cobra.com/downloads/manuals/29LTDCLA.PDF


Thanks!
Dodgem

http://dodgem250.angelfire.com

Posted on May 10, 2008

  • 773 Answers

SOURCE: cobra 29 ltd classic cb not transmitting

Check the ground. Make sure its grounded well on bare metal. To see if the ground is bad, or not making good connection, disconnect the antenna and turn it on. if it does not power up, that means your ground is bad, and it was grounding only through the antenna.

Make sure not to key up with out the antenna connected.

Posted on Feb 08, 2009

audio20
  • 22 Answers

SOURCE: swr meter not moving.

If the radio is working don't worry about the meter unless you absolutely want it. These little meters are not very accurate or reliable. Get an external SWR meter to check the antenna.

Posted on Apr 23, 2009

  • 773 Answers

SOURCE: cobra 29 ltd classic antenna calibration ??

Wow. That's not at all a solution to what this guy is asking. And why all the caps??

The one point jm77437 has that is correct is that you do not set the radio, you set the antenna. The rest is blah blah.

Here is how you tune your antenna for you radio. First off it depends on what kind of antenna you have. most fiberglass antennas have a tunable tip to adjust the height of the antenna. Metal whips either have a collar at the base that the whip will either slide up or down in to adjust the height. The other type of metal whip's you have to physically clip to shorten the antenna, you must be careful with this type because once its clipped, that's it. You cannot add what you cut off.

I am going to give this example using a metal whip with an adjustable collar.

First after your radio is hooked up in the vehicle, drive to an open lot. Buildings and other structures can cause extra reflection. turn to channel 1. Flip the meter to CAL. Key the mic without talking. Now turn the CAL knob up until the needle reaches the little upside down triangle all the way to the right marked CAL. Now you have just celebrated your radio for your setup to measure you SWR. Now while still holding the key, flip the meter switch to SWR. The needle will move, and where it stops is your SWR reading. The lower the better. Anything under 1.5 is considered really good. But still, the lower the better.

Make note of what your SWR was on ch 1.

Now flip to channel 40. Repeat the SWR process. You must recalabrate each time you take a reading.

Now like jm77437 said. If your SWR reading is higher on 40 then 1, then your antenna is too long, and you must make it shorter. Loosen the collar and lower the antenna in the collar 1/4 inch at a time. check the swr each time you adjust the antenna.

If your SWR reading is higher on channel 1, then your antenna is too short. You must make your antenna longer. Do this by loossening the collar and pulling the antenna upward in the collar 1/4 inch at a time, again checking the swr each time you adjust the antenna.

What you want to achieve is having the same SWR reading on channel 1 and 40. then you have the best match you are going to get with that antenna.

If your swr is under 1.5 on all channels, you don't need to fuss unless you are a perfectionist. then by all means go ahead.

If your reading is higher then 3, or your ant light comes on, something is really wrong. Make sure your antenna is connected all the way, and the coax is not damaged.

Its important to have an appropriate SWR because if you do not, you are reflecting too much signal back into the radio, and eventually you will burn out your final transistor, and your radio will be toast.

Some tips: make sure you check the swr with the doors and windows shut. Make sure you are in an open lot. Remember to calabrate ecah time you take a reading. If you have had your radio peaked by a radio shop, and they have lowered your dead key, or have done a swing modification, then the meter in your radio will not work when taking an SWR reading and you will have to use an external meter.

Posted on Apr 24, 2009

  • 773 Answers

SOURCE: cobra 29 ltd classic antenna calibration ??

You should not calibrate the antenna before you install it on the car!! the antenna needs to be calibrated on the vehicle that it is going to be on. Type of vehicle, different mounts, and many other variables can change the amount of reflection you will get.

j0hn9999 did a much better job but left some info out.

Take your SWR readings on channel 1, then on channel 40.... NOW, if your SWR is higher on ch 40 then ch 1, then your antenna is too long and it needs to be shortened. Refer to the antenna instructions on how to shorten the antenna.

If your SWR is higher on ch 1 then on ch 40 then your antenna is too short. You must lengthen the antenna. Again refer to your antenna instructions on how to lengthen your antenna.

You must calibrate each time you take a reading.

Make sure your doors and windows are shut when taking a reading

Make sure you are in an open lot when taking a reading as buildings, trees and other structures can cause reflection and give you an inaccurate reading.

If you adjust the length of your antenna on another vehicle and then put it on yours, the SWR will be off. It will need to be tuned again.

An external meter is better then the one in the radio, but will need to be hooked up in the vehicle you have the antenna on.

If you are not running any kind of power, or do not have a swing kit installed, and the radio is stock, the meter in the radio is more then enough to get a correct SWR reading.

Posted on Apr 24, 2009

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The Cobra 29 LTD has no effects from the factory. Commonly if an aftermarket effect has been installed it may act erratically on startup, for example roger beeps on the 29 tend to activate when you turn the unit on.

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Looking at the schematic TR23 colector ties in with
the power switch ,check D22 it's a 9.1 to 10 volt
zener diode also check C11 an D21.
TR23 shows to be a 2SC1096 I would go ahead and
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Good luck maybe this helped.

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Start with the antenna that you have hooked to it, is it grounded, is the coax in good shape, is the connector in good shape. stuff like that.

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Have Cobra 29 LTD CB Radio w/ bluetooth. Power comes on. Does not receive or transmit. What's wrong?


Sounds like the PLL circuit....... no channel synthesizer will kill the transmit and receive...... bad crystal or IC could be at fault or if someone has attempted to add more channels could also be cause.

Dec 20, 2008 | Cobra 29 LTD CB Radio

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My Cobra 29 ltd classic


Hello MyPete,

You have some form of short circuit in your CB, most likley I would suspect the Power supply or the RF Power Output Amplifier. Here are some basic instruction on how to tell wher the smoke is coming from.

1) disconnect and remove your CB from your vehicle and put it on a workbench
2) remove the cover from your CB and expose the circuit board to view
3) connect your CB to an external 12 volt power source and antenna or a dummy load
4) power up the CB and determine where the smoke is coming from then turn off the power supply to the CB
5) At this point you will need a schematic of your CB (get one from www.servicemanuals.com)
6) find the point on the schematic that relates to the point where the smoke is coming from
7) using a ohmmeter determine which component and or components are shorted
8) replace the shorted and or malfunctioning components.
9) test the system (power on, transmit and receive)
10) close the unit back up
11) reinstall into vehicle
12) run tests again.


This should help

Thank you
Shutle832

Nov 01, 2008 | Cobra 29 LTD CB Radio

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Shorts my power supply when plugged in


do you have boots powering up the signal that can do it

Sep 27, 2008 | Cobra 29 LTD CB Radio

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Cobra 29 ltd nw classic


Yes, Do Not Turn Up Too 500's Way Too Dangerous, The Problem Might Be That Inside Some Cords May Be Rubbing Wrong Or, You Have A Short Cord, If Not Any Of That It Is Probally Broke

Aug 07, 2008 | Cobra 29 WX NW ST 40-Channels Base CB...

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B;owing fuses, wont power up, just smokes


Hi,

Try checking the reverse protection diode. This diode would normally be connected right after the power connector and would be the biggest diode inside. One way to verify if this is defective and causing the fuse to blow is even with the power switch at the OFF position, the fuse will still blow.

If on the other hand, the reverse protection diode is good and fuse will not blow when power switch is at OFF, then the short/defective component is inside. There would only be two (2) major components that can cause the fuse to blow with the power switch to ON, the final transistor and/or the audio IC.

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.

Jun 06, 2008 | Cobra 29 LTD CB Radio

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