I don't know if the 546xx family of scopes suffers this problem, but the 545xx family has a battery maintaining the cal data and clock. When the battery dies, you get a short lived message on the screen about no cal data or something similar. If your scope has a CRT display, the message is gone before the CRT warms up enough to see and it looks like a dead scope. The way to check for this is to do a key down power up, hold any front panel key down while you turn the power on. That will put a different message up that requires user input before it goes away. If you get the key down screen lit up, the battery is a good first guess.
