Cobra 29 LTD Classic Recive/Transmit problems

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Rooster9507
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Cobra 29 LTD Classic Recive/Transmit problems

Postby Rooster9507 » Saturday 20th Apr 2013, 13:29

Radio Make and Model: Cobra 29 LTD Classic
PCB Number:
PLL Number:
Test gear available: SWR Meter, BUt i can get anything I need
Symptoms: When I hook an antenna up to the radio it acts like there is nothing hooked up to it, the audio is so low that it is like there is no antenna hooked up at all. I thought it might be the antenna, so I hooked up another one, samething happens. I got out my old Cobra 20 LTD and hooked up the same antenna to it and I heard all kinds of traffic and all kinds of DX so I know the antenna is good. The PA works great, the Ext speaker works but the audio statis is real low like the speaker. I just acts like the antenna is not hooked up. I used an external SWR meter and the SWR's are great. I bought it off of Ebay (BIG MISTAKE) and here is what part the add said---Cobra 29 LTD Classic tuned and peaked out with a MOSFET Supertune Kit installed---You are bidding on a 29 LTD Cobra thats had a MOSFET 520 Supertune Kit professonally installed--- Any help would be great and thank you very much in advance.

What is working: Everything on the radio is working besides what is stated.

What has been tried:

Did it suddenly happen ?: I bought this off Ebay, it was like this when I recived it.
Anything else that may be of help?:

zodiac
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby zodiac » Sunday 21st Apr 2013, 10:13

If the Final has gone short circuit it will take the receive out as well in most cases.
Check to see what current is being drawn by the radio in RX, it should be next to nothing.
If it's more than about 1/4 of an Amp de-solder the final and see if the receive comes back to normal.
How far is it.
Twice it's length from halfway.

Rooster9507
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby Rooster9507 » Monday 29th Apr 2013, 3:00

The final checked out, someone told me to remove the NF or Noise Filter board, but I don't know where to locate that. is this a smart thing to do? if so can you tell me how to do it? thank you so much

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sonoma
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby sonoma » Monday 29th Apr 2013, 3:32

have you tried a external speaker to make sure the one inside the radio is not bad.

Rooster9507
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby Rooster9507 » Monday 29th Apr 2013, 3:43

Yes, I tired that. The squelch works, the volume control works, the audio is just real low, there is a jumper that came off of L22 and L7, I soldered that back and it worked great, then later in the week I hooked the radio back up and same old problem. I am real new at this so needless to say I am a bit lost. :banghead: Thank you for your help

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sonoma
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby sonoma » Monday 29th Apr 2013, 6:20

you said you soldered the wire back on and it was working. L22 is the vco and it may be out of adjustment. when you heated it it may have started working. and L 7 is a receive can.heating any of the cans will change them some. I would try to align the radio and see if it comes up like it should. do you have the equipment to algn the radio to see if it comes back. the vco needs to be adjusted with a scope to peak the signal. you might even try heating the 2 cans again and see if the receive comes back if you do not have the equipment to do it. this will lead you in to what could be wrong if heat brings the radio back functioning.
here is a link to the alignment of the radio.you will have to copy and paste it in your browser for it to take you to the page.

http://downloads.cobra.com/CB/Models/29-SERIES/29LTDalign.pdf

Rooster9507
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby Rooster9507 » Monday 29th Apr 2013, 12:02

Thanks for the help I Re-soldered the jumper again and its working great so far.

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sonoma
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Re: Cobra 29 LTD Classic Recive/Transmit problems

Postby sonoma » Monday 29th Apr 2013, 12:50

Rooster9507 wrote:Thanks for the help I Re-soldered the jumper again and its working great so far.



if it goes out again I would look at adjustments since heat changed the capacitance of the can when you heat it up. a chance it is off just a little causing the radio to go out when cold. the bottom of the cans could also have a cold solder joint and when you heat the can it makes contact. check in the area of the cans you soldered the wire too.


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