If the scope has been off for a while and I power on I get an error
message screen:

Power up Failures
CMOS: Reformatted

If I cycle the power on and off again the message does not appear. I
have run all the diagnostics and they all pass. Everything on the
scope appears to work properly. I can't find any reference to the
message in the service manual. Because of the time it has to be off
(15-20 minutes) I am suspecting a low battery that is used to save
some memory data. I can't fine any reference to a battery for the
basic unit. I did see a battery on the GPIB interface parts list but
couldn't find it on the board or other documentation. Any one know
what this message means??