Yorkville is a Canadian manufacturer, I think, and you see a fair amount of their P.A. mixers around here. They also made Traynor amps (including the mono-block) that are still around.
A local DIY venue was having some minor issues with their P.A. system (early nineties era) and asked me to clean it out. Scratchy knobs can really ruin a gig. This YORKVILLE AUDIOPRO 1212 is built for durability, not ease of access, and pretty much every screw, nut, and knob had to come off to expose the pots. On the way in there we found a hell of a lot of dirt and dust on the main boards but very little inside the sealed chamber that the pots and faders reside in. The power amp wasn't working but I was told to ignore that since they had external amps. I wanted to take a look but it wasn't my place (it was an on-site job). In the end some contact cleaner and a Shop-Vac were all that was needed to get the mixer section sounding like new. I also fixed a cracked solder on the RCA Aux in. The owner swears the whole system SOUNDS cleaner and crisper now. This particular machine was stamped NOV 16, 1993 and had been collecting dust since then - I can guarantee it had never been opened. A few hours work and a few dollars labour will keep it working for another 20 years!