Does anyone on this fine web site have any useful information or schematic on the Sunn SR-4100 PA powered mixer? My band inherited this and although it is currently works, it makes the occasional loud pops and crackles. None of the eq twisting seems to have any effect on the sound. We'd like to use this for garage rehearsals and are willing to have it gone over by a good tech if it is worthwhile. Thanks in advance for your thoughts.