I need help I have a cobra 25 ltd classic the audio gets very hot and the receive is very very low hardly no audio out as well. Replaced c61 c67 c63 and the audio chip can someone help me with what could be the problem or what might be shorted
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Cobra 25 ltd classic
- Thread starter smoke blower
- Start date
Have a look at the audio transformer. Sounds like maybe it has overheated and been damaged. If the radio had a blown final transistor some time in the past, this can result. Especially if someone used a fuse that's too big while the bad part was still in the radio.
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While you're at that - check to make sure the Audio chip "tab" that bolts it to the side panel - is not causing a short.
The old versions (Read discrete - parts) the chassis to the board ground - does not short to each other DC wise.
Meaning - check the tab of the Audio Chip - to the case of the radio - if it shows a dead short on a DC ohmmeter (DVM) then the reason for overheating is the tab is shorted TO ground - remove the hold down hardware - reposition that heat sink spacer in that goo, so you can put the chip to the panel - carry the heat away, but NOT short that tab to ground.
Also, The output cap from the Chip TO the Transformer - pipes audio - but it is supposed to keep DC from both sides from mixing together - else the chip can be destroyed - so make sure the Cap that sends Audio to that transformer - pull it out (unsolder and remove) - turn on the radio (You won't hear any audio you took out the cap that does this) - if it stays cool, then that cap was bad all along just replace it.
The old versions (Read discrete - parts) the chassis to the board ground - does not short to each other DC wise.
Meaning - check the tab of the Audio Chip - to the case of the radio - if it shows a dead short on a DC ohmmeter (DVM) then the reason for overheating is the tab is shorted TO ground - remove the hold down hardware - reposition that heat sink spacer in that goo, so you can put the chip to the panel - carry the heat away, but NOT short that tab to ground.
Also, The output cap from the Chip TO the Transformer - pipes audio - but it is supposed to keep DC from both sides from mixing together - else the chip can be destroyed - so make sure the Cap that sends Audio to that transformer - pull it out (unsolder and remove) - turn on the radio (You won't hear any audio you took out the cap that does this) - if it stays cool, then that cap was bad all along just replace it.
I replaced the audio chip and the caps around the audio chip and it still gets hot . I did notice that with the antenna unplugged it doesn't get hot as soon as I plug the antenna in it starts getting hot. I replaced c44, C 61 ,c67 ,c63 and still gets hot when antenna is plugged up. Radio did have a blown final
Well I wanted to correct something the audio chip does get hot with the antenna unplugged as well
You can replace, replace - rebuild replace - but still, one thing remains...
IT heats up...
You replaced caps - never hear back about the suggestion I made about removing the output cap FROM the audio chip that goes TO the Audio Transformer and see if it still heats up.
Ok, I can understand...
Ok, you skipped one question though...
It deals with insulating washer and the tab.
Are you finding an insulating flat washer/piece of mica or plastic between the tab and the side panel - did you even find one on the old chip?
And are you reassembling it making sure your tab is not shorting to the side panel?
Then beyond that - what year, or at least look at - the audio chip.
Cobra 25's started to use the 5-pin Audio chip soon after the introduction of the Cobra 25 LE - about 2016 or so. So if your radio is newer - it uses a DIFFERENT audio chip - the one shown earlier.
The OLDER ones used variants of several types. Including a YOUDA chip.
So, look at the radio - locate the old audio chip you replaced and look at the numbers printed on the side of it.
Was it TA7222P, YOUDA1022, or TDA2003/5?
So...
What'cha got?
The concern is a ringing effect, a squeal - caused by old caps that shorted, you may not have found the one causing this - it may work like a cap, but it drifted off in value - causing a ring (instability) - you can't hear because the speaker can't reproduce it, (ultrasonic) the path it takes is in the board using the parts themselves.
OR worse someone modded the radio and you wound up with it. Only now you're replacing parts using THEIR values they had in there originally, might want to rethink that. Some mods require a larger cap to pass more audio - this creates the instability, reduce the values - look at the schematics and review the values used. (393 is 39n or 0.039uF - too large for 7222P)
IT heats up...
You replaced caps - never hear back about the suggestion I made about removing the output cap FROM the audio chip that goes TO the Audio Transformer and see if it still heats up.
Ok, I can understand...
Ok, you skipped one question though...
It deals with insulating washer and the tab.
Are you finding an insulating flat washer/piece of mica or plastic between the tab and the side panel - did you even find one on the old chip?
And are you reassembling it making sure your tab is not shorting to the side panel?
Then beyond that - what year, or at least look at - the audio chip.
Cobra 25's started to use the 5-pin Audio chip soon after the introduction of the Cobra 25 LE - about 2016 or so. So if your radio is newer - it uses a DIFFERENT audio chip - the one shown earlier.
The OLDER ones used variants of several types. Including a YOUDA chip.
So, look at the radio - locate the old audio chip you replaced and look at the numbers printed on the side of it.
Was it TA7222P, YOUDA1022, or TDA2003/5?
So...
What'cha got?
The concern is a ringing effect, a squeal - caused by old caps that shorted, you may not have found the one causing this - it may work like a cap, but it drifted off in value - causing a ring (instability) - you can't hear because the speaker can't reproduce it, (ultrasonic) the path it takes is in the board using the parts themselves.
OR worse someone modded the radio and you wound up with it. Only now you're replacing parts using THEIR values they had in there originally, might want to rethink that. Some mods require a larger cap to pass more audio - this creates the instability, reduce the values - look at the schematics and review the values used. (393 is 39n or 0.039uF - too large for 7222P)
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I checked the audio chip and it has the plastic screw and piece of stuff behind the chip I tested it and it isn't shorted. I replaced some of the caps and it seem to be good now. Sorry it took so long to respond but have had some family issues and haven't had time to do much. I appreciate your help thank you
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