I've googled this topic and can't seem to find anything definitive on this issue.
Any suggestions greatly appreciated! www.FTDX10.com
This is probably not a coding problem, but rather a physical problem. Check to be sure that you have the correct soundcard selected in WSJT-X settings, for both Rx and Tx. If you have the Yaesu drivers installed properly, they should both be USB Audio Codec. Check that the level of the Tx audio (speaker) is high enough to drive the radio. Set audio level so the ALC meter is right about in the middle of its range.