I've had this problem for a a few weeks now and it's absolutely baffling me. The modulation wheel on my Yamaha MM8 is adjusting both the modulation AND the keyboard's volume. I have no idea how this happened as I've had this keyboard since '09 and this problem only recently started. I've searched through the manual and across the internet and can't seem to find a solution to turn it back to modulation-only.
Any guidance to help me solve this issue would be immensely appreciated. Thanks!