The scanner has a squelch knob, so it sounds like the squelch switch is broken or full of dirt. To do anything, you must the scanner apart. Put a box out for the parts and you should have a rag to catch the nasty cleaner. One apart, check the easy things, are the wires (two) attached to the squelch switch? Then take the switch out of the housing. There should be a retainer under the knob, unscrew and remove from housing. You will use contact cleaner (BEST!) The contact cleaner is under pressure. Squirt the cleaner in, let it drip out, repeat 3-7x. Wait a couple of minutes or until you know the switch to be dry and plug it all in and test. Still not working? Unplug and repeat. Still not working? I doubt you can buy the part, but try anyway. They are easy to replace and you have it all apart, right?