I recently acquired an old Cobra 29 LTD made in Taiwan, I hooked up my antenna and power and found some serious problems. First off the receive is extremely quiet to the point where I cant make anything out, secondly there is absolutely 0 TX. The red light comes on when I key the mic but according to my external power meter I have no dead key and 0 swing. The PA function works on the radio too. This radio has been sitting for at least 20 years and is at least 30 years old so Im thinking the radio needs a recap job. I dont think it would be the finals due to not having any RX and 0 TX. For the record I used multiple mics that I know for a fact work fine. I dont have a lot of experience working on CB's so I would like to know if a recap job is a good place to start.
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Cobra 29 No TX Very Weak RX
- Thread starter thatoneredneck
- Start date
Shadetree Mechanic
Delaware Base Station 808
Welcome! For a radio that old, most people would suggest a cap job. Then you can work on the real problems if it has any. Otherwise, finding and replacing just a cap or two that is bad right now, would turn into capacitor wack a mole next week. Our member @Klondike Mike sells some excellent capacitor kits, maybe he will chime in with more information.
Thanks, I figured it certainly would not hurt to do a cap job for the age and extreme temps it’s been exposed to in a garage. The cost isn’t too bad either for a kit.
I haven’t yet gotten a cap kit yet because I have some other projects to tackle first. I’ve done more research and to me the caps are the problem because those old Cobras use uniden boards of which the caps are known for failing. So to me it certainly won’t hurt, once I get around to doing it I’ll get back with you to tell ya if it fixed it.
Yeah Im not sure what else to look for in terms of mine I know the audio chips good because PA works and generally when the finals go out you get some sort of very small deadkey out of it. PLL should be good also. Maybe check out bypassing somehow or replacing the PA/CB switch could be not clicking all the way into cb mode.
Replacing all the aluminum electrolytic capacitors is what I tend to recommend. But usually for a radio that still mostly or partly works.
But ask yourself. Why did the radio end up on a shelf in the first place? Maybe someone changed careers, no longer used it. Maybe because it broke.
If it broke 30 years ago, the fault is much less likely to be a bad cap.
Never assume a decades-old radio has "only one" fault causing trouble.
A second radio you can tune to the same channel as this one is a real asset. If you can tune in even a weak carrier coming from this radio when you key it, this would help to pin down where the transmit problem lies.
Take a coax jumper and plug it into the monitor radio's antenna jack. Back the shell down on the threads at the far end. This makes the center pin into a sniffing antenna. If it can't hear any activity from keying the mike with the plug held near the Cobra's transmit mixer, you have trouble upstream from the driver and final transistors. And simply changing them out because someone suggests it would not make a difference.
Unless it has more than one fault, of course. No way to be sure yet.
73
But ask yourself. Why did the radio end up on a shelf in the first place? Maybe someone changed careers, no longer used it. Maybe because it broke.
If it broke 30 years ago, the fault is much less likely to be a bad cap.
Never assume a decades-old radio has "only one" fault causing trouble.
A second radio you can tune to the same channel as this one is a real asset. If you can tune in even a weak carrier coming from this radio when you key it, this would help to pin down where the transmit problem lies.
Take a coax jumper and plug it into the monitor radio's antenna jack. Back the shell down on the threads at the far end. This makes the center pin into a sniffing antenna. If it can't hear any activity from keying the mike with the plug held near the Cobra's transmit mixer, you have trouble upstream from the driver and final transistors. And simply changing them out because someone suggests it would not make a difference.
Unless it has more than one fault, of course. No way to be sure yet.
73