"The 220ohm resistor on the MC68000 pin 6 (/AS) is meant to prevent the console from crashing under certain circumstances. If it has that factory patch, it's using a FH0001 chip as VDP instead of the "classic" YM7101 VDP. Apparently sometime around 1992 Yamaha re-designed the VDP chip and it had that errata. MD consoles with a Hitachi 68000 and the FH0001 VDP will not have the resistor (also there's a trace cut under the 68000 and a black jumper at the other side of the board).
Without these "erratas" fixed the console will crash a lot."