Talkback adjusting volume?

[Blackcat630]

Buddy called me tonight and said he put talkback into a new Cobra 29. Said he put a resistor across the ext spk and pa on board worked fine. Then he decided to make it variable so he tied the rf gain pot wires together and ran 2 wires to it and back to where he took out his original talkback resistor.. now the talkback works and is variable but when he turns down the talkback his receive volume goes down as well?? Ideas I can pass along??

 

[nomadradio]

Either he accidentally broke the connection from the rear of the radio back to pin 4 of the mike socket, or the mike has a problem.

His variable-talkback control should be wired between the mike jack's pin 4 and ground. Generally this means the 'sleeve' pin of the Ext Spkr socket and the sleeve pin of the PA socket. The sleeve of the PA socket is grounded. The sleeve of the Ext socket gets its ground through pin 4 of the mike socket, then through the mike and then to ground.

Until you place a resistor in parallel with the pin 4 circuit. And that's how you get talkback, by jumping around the receive switch inside the mike.

Quickest test is to unplug the mike and see if it changes the receiver volume at all.

If it doesn't, there has been an interruption in the circuit leading to pin 4. Or the circuit inside the mike.

My bets are on a wire that came unsoldered while the mod was being installed.

73