The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

I just got a cobra 25 ltd in a box of junk radios and I thought I would hook it up and check it out. It TX,s fine but has very low RX audio. It works fine in PA mode and is RXing as I can see the meter moving.I was wondering if the audio ic is done, its a 7222 chip. There is no evidence of any shorts or burnt components and I have tried several different mics but with still the same result.Its a good looking little radio and I see that there are a few mods that can be done to it. Any ideas?
Tnx Bob

Hi Bob,
Try lifting one end of R53 to see if the sound comes back if not check that the squelch is working.

Rick.

Rick I tried lifting that resistor and still nothing, Is there anything else I can try, squelch seems to be working as well as RFgain. I get a loud pop sound in the speaker when I turn the radio on and the PA is working, sounds abit like the old problem I had with the TRC 451, could it be a resistor or cap. that has gone bad ?
Tnx Bob

It could be the diodes in the detection circuit. Part of the front end of the actual receiver.

The receiver speaker audio goes up the mike cord, through the switch, and back down the cord's ground wire on pin 1.

A bum mike cord can kill the speaker audio.

Is the S-meter bouncing around on channel chatter in a normal kind of way? Or is it laying down the low end of the scale?

This could point toward a RF or IF problem if the meter isn't active on receive. If the meter is lively on channel chatter, this would point farther downstream to the audio sections.

BTW, if the transmit audio is good, the TA7222 audio power chip is fine, too, no matter what the receiver sounds like.

73

Ok , well the meter is moving freely and there is just a hint of audio output in the speaker with the volume turned up all the way. The mic checks fine and have tried other mics that are known to be ok still the same result. Its not much of a radio , but I would still like to get it going anyway.
Tnx Bob

Bum external speaker jack?

73

I have found a couple of diodes that were bad as well as 2 TR's gone also, but it's still the same symptoms. Anyway I'll still plug away at till i get it going
Bob

Well I have found the problem with the Cobra 25, it was a bad trace running from R97 to R51, I jumped the trace with some wire and also touched up some of the solder points on the board. My thanks go out to Rick for his help via email, Rick you are the man , thank you, I hope this info will be of some help to others in the future.
Bob