A few questions for debugging:
Do you hear the "startup" sound, that is played when the MBSID is fired up?
Have you tried turning the "cutoff" encoder so that it displays FFF before playing any patch?
Do you hear "chip noise", i.e. noise from the SID, that is always present, even if nothing is played?
Have you populated your SIDs right to left (in case you have less than eight) ?
Have you selected the right voltages for the right type of SID?
Have you measured voltages while the MB6582 is powered on? (Between Pin 14 and 28, between Pin 14 and 25 on the sid chip sockets)?
Do you have the feedback mod installed? If so, you could just "pull the plugs" going to the feedback pots, for a test..
Have you tested individual sidpair outs vs the mix out?
Edited by Hawkeye, 28 June 2012 - 20:50.