Hello Steve, I have an original hard copy MX-55 Operation and Maintenance Manual, 7th Ed (Nov 1991). Mine covers the MX-55T-M (NAB 2trk 2ch with center time code track - meterbridge), MX-55T (same - standard), and MX-55N-M (NAB 2trk 2ch - meterbridge) models. It has operating and maintenance instructions, PC board layouts, and circuit diagrams. If this will work for you, I can try to scan it. Send me a PM.
Phil