Cobra 139xlr 40 cn SSB no audio, carrier ok

Your welcome. I hope I was able to give you enough info to get it working. Many years ago I owned the cobra cam 89. It was a nice radio too. I remember looking at the cb radio magazine wishing I could have had enough money to buy the 139 since it had SSB. Anyway, good luck with it.

 

If it does happen to be the audio chip, here’s a video showing how to replace it with a TA7222AP. Although if it comes to that, may want to take it to a CB tech.

 

quick test, go on sideband and see if you can get any power out when you speak into the mic, if you don't, it isn't the chip.

 

Yes, the audio for side-band doesn't use the IC4 audio amp, it uses the mic IC3 amp. There are I think five transistors and one IC before the IC4 is used for anything. The audio for SSB from the mic goes to an IC3 that amplifies the audio then goes to the dynamic control than gets divided up for AM or SSB. Another easy test if you have a scope is to see if you get anything off of any leg on the dynamic control.

By the way, stupid question, if the dynamic control all the way open?

 

I might add, capacitor C103 is a 10 volt 470 microfarad capacitor that goes to relay K3, which supplies audio to the speaker and external speaker jack. Also on the receive side, there is C104 which is a 10 volt 330 microfarad capacitor that is part of the output from the power supply. It’s possible that one of these maybe bad. With older radios like this 139, it’s best to replace the 10 volt caps with at least 16 volts. Seems like this radio has a handful of 10 volt caps in it. Just something to keep in mind.