Marantz NR1506 Owner's Manual page 173

Contents Connections Playback Settings Tips Appendix
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
0 Only use this function if so instructed by a Marantz serviceperson or installer.
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Front panel Display Rear panel Remote Index