Image is taken from the manual. From the looks of it pretty much a straight forward audio amp all the way back to the Volume control. The TX Mute Switch looks like it's supposed to short the audio path to ground during transmit. It sounds like it's supposed to reduce click and only operates briefly. Maybe in your case it "on" all the time and shunting audio to ground?
I'm not sure what you mean by Ch 1 and Ch 2. You may be referring to sections A or B?
One suggestion is to remove Q7 and and see what you get on Receive. You should also be able to put a finger on the wiper of the Volume control and hear a very strong hum/buzz in the headphones.
Another approach would be to use another audio amp connected to the "high" side of the Volume control and see if you hear static.?
Again, good luck!!
--Al
