Yamaha PCB abbreviations

I'm working on a Yamaha AV-55 surround sound receiver--with no sound--and no schematic.

Am presently investigating the PCB labeled 'protection' as voltages on the protection IC seem way off. The cable that may be the source for the IC Vcc is labeled DC, OC, VL, VR. Do DC and OC in this case have a standard meaning?

I've also seen M+ and M- on some boards, and wondered what they typically signify.

Thanks!

Could it (OC) be Over Current? or Open Circuit