Marantz AV-9000 processor loses its mind ...

I also have an AV-9000 with intermittant amnesia.

According to the User's Manual, the unit has memory that should retain settings if the power is lost for up to a week. See the "Memory Backup" note on page 34 of the manual. It states that the unit needs to be On or on Standby for 8 hours for the backup to work, which implies that it operates off a charged capacitor, NOT a battery. Assuming that you've had it powered on long enough for the backup to work, the problem might be a faulty capacitor. However, it seems unlikely that all of us would have the same bad cap. I think it's more likely that some design flaw allows an internal spike when the power is restored to zap the memory contents.

Here's the strange part that I notice with my unit. I can shut it off and disconnect the power cord for hours at a time, but it properly retains the settings when I turn it back on. However, if I leave it in Standby and the power blinks off, the memory is history. This suggests that I'm better off turning off the unit with the power button than leaving it in Standby.

Other people with this problem, was your unit Off or in Standby when it lost its memory?

Mine has been either On or in Standby when it loses memory. I suspect you're right about the design flaw; I've talked to others with the same problem.
Rich

mine loses its memory when it has been switched off from the switch for a longer period of time.

there is a memory capacitor that goes bad and can be replaced .