Hi, my Yamaha MM8 powers on but when I plug in my head phones, there is NO SOUND. I plugged it into my amp (using the standard 1/4 inch cable- in fact I tried 3 different cables, to no avail). YES I checked all of the "basic" possibilities - volume control, head phone Jack removed completely). I read on line to ensure that 'local control' is ON. (I'm about to check that now). In case that doesn't solve the issue, could it be the input jack?