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Cobra 1000 final is good driver is good audio ic good radio does not receive or transmit. could it be the keying transistor? if so what number in the radio is it

Radio does not receive or transmit. could it be the keying transistor

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Could be

Posted on Jun 05, 2014

6 Suggested Answers

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  • 2 Answers

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Posted on Jan 02, 2017

SOURCE: cobra 148 gtl

First take a jumper wire and connect it to the DC Ground of the input of the radio then touch it to the TX pin on the radio if it does keyes up then its in the mic or mic cord on the end of the mic plug or where it goes into the mic cable goes up inside the mic. If the radio don't key up at all then check the main voltage regulator chip one pin will have 8 volts transmit and another pin will have 8volts recieve. If you get no switching DC voltage on the regulator then its bad and needs replacing there is also a known bad capacitor in the radio thats only 10 volts change it to 25 volts at the same capacitance.

Posted on Jan 08, 2008

  • 773 Answers

SOURCE: Cobra 29LTD CHROME low tx no mod, rx good low Vol, talkback good

1 why would you change the finals?? Have you checked you antenna? How are your SWR's? Crappy antenna's cause a lot of problems.

Use an external meter to see what the SWR is, and see what the output is PEP. If its low, then there is something wrong. If it is High, change the mic and turn up the dynamic all the way.

Next. Have you been messing around in there?? Tryin to get more wattage? You turned VR4? If you thought you were turning it up by turning it all the way to the right, you turned it all the way down. Turn it all the way to the left.

Posted on Jun 17, 2009

  • 86 Answers

SOURCE: rci 2950 no audio period rx or tx

Check TR38 I have seen caps in the circut
go bad more then once if you have a schematic you should be able to find it if one
is bad,a capasator meter would help but you
can check them with a ohm meter.
Good luck.

Posted on Sep 16, 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

  • 773 Answers

SOURCE: 29 cobra ltd c.b. wont transmit or receive

make sure the RF gain is all the way up, and the dynamic is all the way up or most of the way up.

When you say the antenna is good, have you checked the SWR's and or have tuned the antenna to be the correct length for the radio? If this has not been done ever, your radio could be a brick.

Also, make sure the PA/CB switch is on CB. if its on PA(public address) it will not receive or transmit because it is on PA mode, which if you have one hooked up, a PA speaker, then you can talk to people through it out side your car.

Also, make sure the S/RF SWR CAL switch, its the first one on the left, is all the way up on S/RF. this is your signal/ receive setting for the meter. When you hold the key, does this needle swing forward? As well does the RX/TX light turn red? If it does, then the radio is transmitting.

There is another light on the radio under the TX/RX light. It is the Antenna warning light. If this light comes on when you transmit, or has come on all the time during transmit, and now it doesn't then the radio is a brick. That is a warning light. It means that the antenna is not matched, or has not been tuned to the radio. If this has not been done ever, you have killed the radio.

Here is why. When you transmit, you are sending off a radio wave. This radio wave, at 27mhz, is about 36 feet long. In order for the wave to radiate off the antenna, the length of the antenna has to match the length of the radio wave. Now it does not have to be a full 36 feet. It can be an exact multiple of 36 feet. In other words it can be 1/4( one quarter) or 5/8(five eights) of a wave in length. 1/4 of a wave is 108 inches, or 9 feet long. Your antenna is still probably does not seem 9 feet long, but there is usually a loading coil that is not exposed making up the rest of the length of antenna, so that it matches the length of the radio waves electrically. If you were to stretch the coil out with the antenna whip, it would be 9 feet long.

When the antenna does not match the wave length, part of the RF energy does not leave the antenna, and goes back down the feed line(coax) and hits the transmit transistor. Prolonged reflection to the transmit transistor, otherwise known as the final will blow it out. As well depending on how bad the length was off, the more off, the more reflect energy, the more RF energy you are blasting back into the radio, and this causes more things then just the transmit to blow out. Some time the receive goes along with it when it finally goes.

So if the RF gain is up all the way, which by the way is basically how much receive you have, and there really is no reason to have it down at all, and the CB/PA switch is on CB and the needle does not swing forward when its on the S/RF setting, chances are that the radio is now no good.

It is fixable, but if there are no CB shops near you then you will have to send it out. And Cobra will not cover this under warranty because its stated in their warranty that they do not cover damage due to high SWR.

Posted on Apr 06, 2010

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No audio transmit or recive


check your final for voltage, work your way from IC 1 on up then check audio transistor . Work your way through the transmit section then the receive section . Check your volume control ,make sure its working alright Just have patience and it might jump right out at you.

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If theres no carrier its either the finals or driver. If theres no audio its the white wire in the plug that screws into the radio..its either broke or most likely come unsoldered. It keys but no audio.

Mar 05, 2015 | Cobra Radio Communications

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Cobra 1000 will not receive or transmit.


Sounds like a problem with the VCO / PLL Circuit since nothing happens in RX or TX. Check to make sure you have the correct supply voltages to start with and also check to see if you have 10.240Mhz. Use the service manual and go through the PLL/VCO alignment section. If anything is missing then you at least know where to look.

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Cb problem have a cobra 19dx iv with a 2ft magnet mount cobra antenna swr is good, receive is good, but muffled output


Hi and welcome to FixYa,

Which output is muffled, transmit (modulation audio) or receive audio?

If you are referring to the receive audio, initially, have you tried an external speaker? If it works good, then it would be an internal speaker problem; if not then others to check would be:
  • IC1 - KIA7217AP audio IC;
  • CM 10 & 15 - audio output capacitors 470uF / 16V.
if it were transmit / modulation audio, try replacing the mic.

Please postback updates.

Good luck and thank you for asking FixYa.

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2 Answers

Cobra 1000 GTL by Dynascan


This is a complicated modification. I have never done it to a 1000 GTL, but its done basically the same in all radio's.

I don't recommend doing it, especially since I am not 100% sure on how exactly to do it. I have never been in a 1000 gtl. If I had one in front of me I could tell you for sure how to do it.

If the reason for Variable power is a linear, just a swing kit in for the dead key you need, most likely 2 watts, and leave it.

Here is how to do a variable power mod. this is assuming the swing mod is done the same to this as a cobra 25/29 or uniden 68/76 etc.

If you would like to try it, here it is.

You get a TIP31 transistor, Radioshack has them.

Where you put the swing mod in the radio, which is a cap and a resistor, you put the TIP31 and cap. A 47uf cap works fine.

With the resistor facing you, and the tab in the back away, solder the cap to the transistor. the leg with the black stripe goes on the right most leg. then the other goes to the center leg of the transistor.

Solder a wire on the left most leg, long enough to reach the front of the radio. Now solder the 2 legs that don't have the wire on it, in the place where you would put the swing kit, with the black stripe on the cap facing the back of the radio usually.

Remove the wires from the RF gain and solder them together.

Now solder the wire from the transistor to the center tab.

Remove VR6 and solder a wire from the top tag of the RF gain to the top connection of VR6 that you removed.

Then connect a wire from the bottom tag to a ground point. The side of a tuning can works fine.

Take a piece of shrink tube and put it over the TIP31 so it does not ground against the heat sink, that would be bad.

This is done basically the same in all cb radio's.


Apr 07, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

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.

Dec 18, 2008 | Cobra 29 LTD CB Radio

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