so this has been driving me nuts for about three weeks now. i have a yaesu ft-7900r mounted under the dash of my f150 and randomly the audio just drops out, like completely silent, and then comes back. sometimes it happens when i go over a rough patch of road, sometimes it happens for no reason at all while im just cruising on the highway. first thing i did was check all the connectors, the power leads going to the battery, the mic connector, all of it looked solid. swapped the mic cable too just to rule that out.

the thing is it doesnt lose the signal entirely — i can still see the squelch light doing its thing on the display, so its receiving but just no sound coming out. then a few seconds later it comes back like nothing happened. its mounted pretty solidly i thought, used the standard bracket and its not rattling around or anything. anyone dealt with something like this before? im starting to wonder if its internal, like a cold solder joint somewhere inside the unit itself. radio is maybe 5 years old, bought it used.

had almost the exact same thing happen with a 7800 a while back. turned out to be the speaker wire connection on the back of the radio — not the external speaker jack, but the little internal speaker lead inside. if the previous owner had it apart at some point the connector in there can work itself loose over time especially with vibration. worth pulling the covers and just reseating everything you can see. also check if the external speaker jack has anything partially inserted, sometimes a loose plug in there will cut off the internal speaker and if the plug isnt fully making contact you get that intermittent thing you're describing.

could also just be the volume knob itself, those encoders get dirty and the contact gets flaky. try spraying a little deoxit in there and working it back and forth a bunch of times. fixed two of my radios doing that. cheap fix before you start pulling it apart anyway.