Modulation is low and distorted, no receive audio, no PA audio. Just put a new 2003 audio chip in it and the fact that it is modulating means that it's doing more than it was. If anyone knows what I should look at I would like to hear from you
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Cobra 29 LX audio issues
- Thread starter Uncle Ronnie 336
- Start date
Overheated (melted) audio transformer T1?
Does the radio receive? If so, how does that sound?
You didn't say.
73
Does the radio receive? If so, how does that sound?
You didn't say.
73
I can't hear the receiver, only that little almost pop sound when it goes from transmit to receive. and there's no PA audio when I put a speaker into the PA Jack. I only get choppy distorted modulation on transmit
Got any history on the radio?
When power is applied in reverse, takes out several things - including capacitors.
When you say low audio - the audio chip itself trying to push power thru the circuit to get to the speaker - even the speaker wires is they are shorted - can generate a condition like what you describe.
Things like the Audio amp - get really hot too...
Make sure the SPEAKER is not shorting it wires to ground at the case (check the spyder that the cone and wires rest in, make sure it's clear and do up an ohmic check to make sure it's cage is not shorting to any of the speaker wire leads.)
When power is applied in reverse, takes out several things - including capacitors.
When you say low audio - the audio chip itself trying to push power thru the circuit to get to the speaker - even the speaker wires is they are shorted - can generate a condition like what you describe.
Things like the Audio amp - get really hot too...
Make sure the SPEAKER is not shorting it wires to ground at the case (check the spyder that the cone and wires rest in, make sure it's clear and do up an ohmic check to make sure it's cage is not shorting to any of the speaker wire leads.)
When I first got the radio it had a blown protection diode which I changed out, the final was only putting out a watt of carrier no matter where I tuned it so I put a mosfet in there and was only getting 5<25 watts after a bunch of fiddling. So I was willing to play around with the modulator chip thinking maybe I could make that put out more power (lol) and my dumbass took out that little jumper that connects ground to the negative inverting input not even really looking at the chips pin out so yeah that thing went quick after doing that, it was a freebie radio so it's not like I lose my ass on this, but I really should have left well enough alone or tried some different mosfets because I know they vary widely in terms of gain. So that's about the history of it. The new chip is in there and it does something, and I changed out every electrolytic cap that is directly connected to a pin of that chip
Was it originally a MOSFET? If not, did you also change the companion parts when you added it?
That "pop" sound and a blown protection diode...
Yieesh - this ones got an LX - which means it has that special display and logic panel - there is a Relay (2 actually) located on that logic front panel - so if you've got this radio and you don't know what happened except for reverse polarity - this will be a labor of love, you might hate it, but truthfully; this may have far more problems than it's worth to fix.
The LX model also comes with a WX function - so if that doesn't work, might mean the logic board itself is toast - for the CPU itself has to "control" everything - including thru relays that handle the speaker.
So if you've checked the speaker and see that it's not damaged and you don't hear anything thru an external speaker or PA - then the routing to the front panel from the main board is already suspected to be part of the "cause" - and the other damage may localize to a simpler relay or blown trace but the boards used in the radio require some foreknowledge of how they are put together to take them apart. They are intricate.
If you have some time you can visit CB Tricks - an older deprecated site that used to have some great forums but still can serve as a repository for older CB radios and they do have some information about the LX-style radios.
Worth a look to see if it can help you...
http://cbtricks.com/radios/cobra/29_lx_le/index.htm
While I was out there looking for some info to possibly shorten the time in trying to find a solution - I came across this vid... this too might be worth a look...
Yieesh - this ones got an LX - which means it has that special display and logic panel - there is a Relay (2 actually) located on that logic front panel - so if you've got this radio and you don't know what happened except for reverse polarity - this will be a labor of love, you might hate it, but truthfully; this may have far more problems than it's worth to fix.
The LX model also comes with a WX function - so if that doesn't work, might mean the logic board itself is toast - for the CPU itself has to "control" everything - including thru relays that handle the speaker.
So if you've checked the speaker and see that it's not damaged and you don't hear anything thru an external speaker or PA - then the routing to the front panel from the main board is already suspected to be part of the "cause" - and the other damage may localize to a simpler relay or blown trace but the boards used in the radio require some foreknowledge of how they are put together to take them apart. They are intricate.
If you have some time you can visit CB Tricks - an older deprecated site that used to have some great forums but still can serve as a repository for older CB radios and they do have some information about the LX-style radios.
Worth a look to see if it can help you...
http://cbtricks.com/radios/cobra/29_lx_le/index.htm
While I was out there looking for some info to possibly shorten the time in trying to find a solution - I came across this vid... this too might be worth a look...
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Yeah what sucks is that I could have left well enough alone and it would have been fully functional. So when I'm trying to modulate if I go ahhhhhhh and start quiet and increase my volume it doesn't do anything until I get to a certain loudness. And it doesn't sound good. I'm hoping I didn't take anything in the front panel with it when I decided to mess around with the modulator trying to get more juice out of it like a dummy. Looks like I'm going to be rained off of the job site tomorrow so I'm going to try to mess with it more