I have a later revision Wm2(2) that has a logic board quite different from the service manual easily found online. It has a single amp ic (301) vs the 2 shown in the manual 1. Replaced centre gear - all transport features working fine 2. No sound - sound was fine prior to centre gear replacement. All wires appear to be fine So.. Is there a later service manual available? What is the best way to troubleshoot no sound?