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Cobra 29gtl Audio Flutter Mod
- Thread starter Probate
- Start date
Pretty sure I have a picture of where it goes on the most-common circuit board version. I'll see if I can turn it up.
73
73
Late to the game, but if the audio flutter which sounds almost like a 'motorboat' while you are talking / transmitting, I found an older post that may alleviate the issue: "...'Motorboating': Locate C 242 (.001uF) on pin 5 of TA7222 audio ic and move to pin 4 of ic...". From what you described, it was similar to a case of a 'motorboat' sound I could hear on my end while my friend who had Hong Kong made 29GTL was talking / transmitting.
Just noticed you said "Gee Tee Ell".
That makes the radio 40 years old or more, pretty sure. If the radio has a lot of miles on it, might be time to replace all the electrolytic caps. That kind of component is built from materials that predictably degrade from age alone. And if it's used a lot, this just speeds up the inevitable failures.
Most of them serve to prevent feedback between separate circuits. If one of them fails from age, the unwanted feedback you get might have a high pitch, or a low pitch like the note of a motorboat.
And if you can find someone with mad troubleshooting skills, he/she could identify which failed capacitor is the culprit and replace just that one or two. But after four or more decades, you'll end up repeating this process as additional caps fail down the road. We call this "electronic whack-a-mole".
If the radio were NOS and had never been used, all those caps might still work just fine. But there's no odometer on the radio to judge the mileage. If I had to play pin-the-tail-on-the-donkey here I would suggest changing the main filter, usually the biggest one on the circuit board, typically near the TA7222P audio power amp chip that's bolted to the side rail.
Wouldn't waste much to try, even if it doesn't fix the fault. If changing one cap stops the noise, you can decide what to do when the next one goes bad.
Best source of a complete kit of capacitors for a radio is a member here, Klondike Mike.
Here's the one he sells for that radio:
https://klondikemikescapkits.com/pr...pacitor-kit?_pos=2&_psq=Cobra+29&_ss=e&_v=1.0
Best reason to patronize Mike is that he uses quality parts. The cheapest chinesium capacitors might or might not be totally up to snuff. Ebay is rife with cheaper stuff, but I don't trust it. Our shop uses his kits. We have an extensive stock of this kind of part, but my labor to pick three dozen of these off the shelf costs me as much as what Mike charges for the kit. Saves my customer money and the aggravation of having a low-ball part go bad later on.
Or you could just by a used 29LTD that's only ten or fifteen years old.
73
That makes the radio 40 years old or more, pretty sure. If the radio has a lot of miles on it, might be time to replace all the electrolytic caps. That kind of component is built from materials that predictably degrade from age alone. And if it's used a lot, this just speeds up the inevitable failures.
Most of them serve to prevent feedback between separate circuits. If one of them fails from age, the unwanted feedback you get might have a high pitch, or a low pitch like the note of a motorboat.
And if you can find someone with mad troubleshooting skills, he/she could identify which failed capacitor is the culprit and replace just that one or two. But after four or more decades, you'll end up repeating this process as additional caps fail down the road. We call this "electronic whack-a-mole".
If the radio were NOS and had never been used, all those caps might still work just fine. But there's no odometer on the radio to judge the mileage. If I had to play pin-the-tail-on-the-donkey here I would suggest changing the main filter, usually the biggest one on the circuit board, typically near the TA7222P audio power amp chip that's bolted to the side rail.
Wouldn't waste much to try, even if it doesn't fix the fault. If changing one cap stops the noise, you can decide what to do when the next one goes bad.
Best source of a complete kit of capacitors for a radio is a member here, Klondike Mike.
Here's the one he sells for that radio:
https://klondikemikescapkits.com/pr...pacitor-kit?_pos=2&_psq=Cobra+29&_ss=e&_v=1.0
Best reason to patronize Mike is that he uses quality parts. The cheapest chinesium capacitors might or might not be totally up to snuff. Ebay is rife with cheaper stuff, but I don't trust it. Our shop uses his kits. We have an extensive stock of this kind of part, but my labor to pick three dozen of these off the shelf costs me as much as what Mike charges for the kit. Saves my customer money and the aggravation of having a low-ball part go bad later on.
Or you could just by a used 29LTD that's only ten or fifteen years old.
73
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