I found a manual at this address
but I cant find error 73 anywhere. My only guess is that it is error 93 and being displayed wrong? Otherwise shame on otari for not listing all the errors in the manual.
http://classes.berklee.edu/mpe/pdf_f...otari_mx80.pdf (20+MEG pdf)
http://classes.berklee.edu/mpe/pdf_files/manuals_pdf/
Otherwise the site above has tons of pdf manuals.
William