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Cobra 29 ltd Chrome, No RX sound

longhaireddwb

W9WDX Amateur Radio Club Member
Oct 8, 2008
555
30
38
Colorado Springs, CO
This is an odd one to me. Hoping someone can point me in the right direction.

I used another radio and I hear that the cobra 29 LTD chrome is transmitting. I also see on the meter that I'm getting RX from the other radio. When I turn the radio on I get a pop so I know the speaker is good and connected. I can also hear the factory talkback thru the speaker. Still, no RX sounds. I hooked up my Sig Gen and Freq counter and I can see signal getting to the meter and its TX on freq.

I've done a little tracing with my Signal Tracer back from the SO239 and I've got RX all the way to the Ext Speaker jack, also if I connect my Tracer to the speaker wires I have sound.??? It didn't make sense but I replaced the speaker and that didn't help. When I plug in an ext speaker I still get no sound!

I pulled TR13 and then got sound so I tried replacing TR13 and back to nothing. I've worked the hell out of the control pots as This radio was in a dirt truck and was covered in dirt and dust. Controls are now no longer scratchy and the RF Gain pot seems to be working along with the volume. At least when I connect my signal tracer to the speaker wires, BUT, Squelch doesn't work at the speaker wires with my signal tracer connected. Not sure why I can get sound (AF) with my Tracer connected but not a speaker.

I'm leaning towards the Squelch circuit but it's just a feeling. I'm about lost and am dumfounded in where to go next. Anyone run across something like this before? Can you help get me back on track to find the reason I get no RX sound? I've flexed the board trying to find a broken trace and have spent some time staring at the traces and solder joints and see nothing bad going on. Even touched up a few that I wasn't completely happy with.

Help, please. I don't want this radio to go into the parts box as whatever it is I feel it's simple. I'm just overlooking something.

Jerry...
 

try jumpering out the external speaker jack.

these can get worn out, and if you look at the schematic, there is a connection there that goes to the speaker. it is touching when there is nothing plugged in to the jack, and plugging in an external speaker jack breaks that connection.

here is a diagram:
29ltd.PNG

get a piece of wire, and tack solder one end to the NON GROUND side of C50. the side that goes to the CB/PA switch.
tak solder the other end of this wire to the side of R51 that goes to the EXT SPEAKER jack.

did your receive come back?

if not, its not the jack and your search continues.
LC
 
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Thanks for the reply LC. I gave it a try and that wasn't the answer to the problem. I put in a jumper to by-pass as you said. It was worth a try. Thanks for the Idea.

I've replaced a couple of these jack before so I've seen this issue. Still seems odd that with my Tracer on the speaker wires I get sound (AF), but the squelch doesn't change the RX. Just dont make sence to me. Maybe the 9vt battery in the tracer is supplying voltage and something else isnt???
 
FOUND IT!

The vol/squelch pot!
The wire that goes to the board ground off of the squelch part of the pot had broken off. I was tracing the squelch as I just had a feeling. Went back to the main pot and checked the wires. Found a black wire broken off. Soldered it back and wa-la! Sound. The squelch part of the circuit was not completed back to ground so it was an open circuit.

Boy, this was a pain and I had a feeling it was something simple. I just had to spend a lot of time tracing things out. This still doesn't explain why my Tracing tool was picking up the AF and making sound at the speaker wire. But it does explain why I had no sqelch change at the pot.

Thanks to LC for trying to help. It was a valid area that has issues and a good idea. Just not the answer that fixed it.
As they say on the radio. Going back silent for a while. You may see me again in a few months. I dont post much but have been lurking for years.

Jerry...
 
awesome glad you found it.
you just reminded me that i have a chrome 29 around here somewhere that i need to take a look at!
LC
 

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