Marantz NR1605 - Manual (Page 200)

Maintenance Mode
Use when receiving maintenance from a Marantz service engineer or
custom installer. Ordinarily, this mode isn’t suitable for use by the end
user, only by a trained service technician or custom installation
professional.
NOTE
Only use this function if so instructed by a Marantz serviceperson or installer.
Contents Connections Playback Settings Tips Appendix
200 Front panel Display Rear panel Remote Index