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Mysterious Cobra 29 LTD not working!

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jluck001

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Jun 13, 2020
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So my friend from work gave me his older Cobra 29 LTD (The one with the mic plug coming out the side instead of front) for use in my Jeep and I was super excited to try out this new piece of kit but there is a big problem. Once all hooked up the radio does not receive anything, no static, nothing. When I key the mic, the SWR meter doesn't move at all and the TX/RX light along with the channel display goes completely black. I also cannot hear anything coming out of my PA speaker when switched to PA. I opened the radio and took a look inside (pictures below) and saw what looked to be modifications to the main board but I am not sure if it was just built that way. Has anyone else had this problem?

Any input is greatly appreciated!
 

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mmckenna

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Those don't look like modifications. The first photo appears to be two capacitors that are there to suppress some noise on the power input.
Not sure what the second photo is, but a capacitor to ground.
Third photo is a resistor, but looks stock.

If the radio won't do anything when you key up:
Make sure you are feeding it with 12volts DC off your vehicle battery or a power supply large enough to supply 3 or 4 amps.
Make sure you have a properly tuned antenna installed.
Make sure you are using the correct microphone.

If it still doesn't work, you may have to see if someone knowledgeable in these radios can assist. Or just ditch it and buy a new CB for $40.00.
 

RFI-EMI-GUY

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Dec 22, 2013
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Hard to say. My first thought was wrong or bad mike because the T/R switching sometimes all happens in the mike. But you should have some lights on the panel. What about the fuse? I agree those are factory parts not some goofball golden screwdriver mods. It is worth more unmodified even if broken.
 

RFI-EMI-GUY

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Where are you getting power to run this radio? The newer Jeeps require some $35 adaptor to get switched power from the ignition.
 

spongella

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Wondering if he found the problem. Excellent suggestions have been posted.
 

WB9YBM

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Once all hooked up the radio does not receive anything, no static, nothing. When I key the mic, the SWR meter doesn't move at all and the TX/RX light along with the channel display goes completely black. I also cannot hear anything coming out of my PA speaker when switched to PA.

All audio is processed through a single I.C. that handles squelch, amplification to the speaker & P.A. speaker, from the microphone, etc. Sounds like that I.C. might be blown. The ones I've seen don't look like a typical I.C. in that it has only a single row of pins (instead of the usual two), is stood up and mounted to a heat sink.
 

138BG

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Jul 10, 2019
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Any side mic 29 has been around for a while. Lots of aging component issues possible. Close inspection of solder side (magnifying glass maybe) could reveal cracked solder joints from mods or age. On component side check closely for areas where brown glue was used to secure larger components (large caps, crystals, inductors, transformers, etc.) Over time the glue turns corrosive and conductive, will eat component leads and board traces. Have all electrolytic capacitors been changed? They are all probably past their expected lifespan. Just a few of the likely possibilities.
 

138BG

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Maybe the info will help someone else with a similar situation then. Lots of great old Uniden boarded radios still around with the potential nasty glue issues.
 
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