Twenty years ago or so I posted pics showing how to "lock" the clarifier on a RatShack TRC-457 base CB. Has the same pc board as a whole list of 1978 radios, but the mobile version sold by Cobra is different. The control wires on the base station connect to the solder side of the pc board. The Cobra 138XLR has all the wires connected to the component side.
So the pics for the base radio don't quite work for the mobile.
First step is to remove D30. I only took one end loose here, but you can remove it altogether. Probably should. This disconnects the transmit-only voltage that powered the trimpot that took the place of the front-panel control while transmitting.
Next remove R119, a 100-ohm quarter-Watt resistor. Be nice to it we'll need it for the next step.
Here's a wide view of where R119 will go.
Closer up, makes the solder pads where it gets connected a bit clearer.
The sharper-eyed reader will see that one end of R119 has gone back where it was to start. The other end is now connected to a continuous voltage source, to make the front-panel clarifier control active all the time, both for transmit and receive. This makes it easier for a three-way or more conversation with all the participants transmitting on the same slot.
Enjoy at your own risk.
73
So the pics for the base radio don't quite work for the mobile.
First step is to remove D30. I only took one end loose here, but you can remove it altogether. Probably should. This disconnects the transmit-only voltage that powered the trimpot that took the place of the front-panel control while transmitting.
Next remove R119, a 100-ohm quarter-Watt resistor. Be nice to it we'll need it for the next step.
Here's a wide view of where R119 will go.
Closer up, makes the solder pads where it gets connected a bit clearer.
The sharper-eyed reader will see that one end of R119 has gone back where it was to start. The other end is now connected to a continuous voltage source, to make the front-panel clarifier control active all the time, both for transmit and receive. This makes it easier for a three-way or more conversation with all the participants transmitting on the same slot.
Enjoy at your own risk.
73
