Tech: Rock ola 480 volume went low and wond now wont go up HELP

Hi all, hopefully somebody can help me out. I got a Rockola 480 and while
playing the volume just suddenly died. You can still here the music through the
speakers but it is softly and turning up the volume will not change anything at
all. I checked out the amp board and all looks okay. Anybody have any idea what
would cause this and where I should start looking? If i need a new amp board
anybody have one for sale? thanks for your help group...