There is a VCV circuit with a small vaariable capacitor.? Sounds like it is out of range which is common on the FT-980.? Use a non metalic tool to adjust.? You should get the same tone on LSB as USB once in range.? I hope you have the Yaesu Tech supplement manual which is the Yaesu Tech? Manual for the for the FT-980.? The capacitor can be reached by removing the top cabinet cover.? Good luck.?