Be sure to add me to your favorites list Yamaha Original Service Manual Book for the Yamaha SPX50D Rack Mount Digital Sound Processor Unit. Great, original Yamaha service manual for the Yamaha SPX50D Digital Sound Processor. This is a full service manual, with specs, block diagrams, panel layout, circuit board layout, dis-assembly, several schematic diagrams, full parts list, overall circuit diagram and more. In good to very good condition and would be very helpful to work on and repair your SPX50D. Original Yamaha document, printed in Japan, from 1988. This is a manual or document, this is NOT a piece of equipment or instrument. If you have any questions, I'm always happy to answer them. Thanks for looking, Check out my Store!