Here is the procedure:

The PCM70 has extensive protection against power line noise, etc. but can
still have its memory become scrambled by power line noise, glitches, etc.

You can try the following to correct the problem. BE AWARE however, that
the second option listed here WILL CLEAR THE ENTIRE MEMORY, INCLUDING
REGISTERS.

First:
Turn off the power switch for a few moments, then turn it back on. When the
software version number appears on the display, press the 8 key.

After a few moments you will be asked:
CLR ALL BUT REGS
Press the LOAD key. The display flashes:
CLEARING

If this fails, try the following: (REMEMBER, ALL MEMORY CLEARED)

Turn off the power switch for a few moments, then turn it back on. When the
software version number appears on the display, press the 0 key.

After a few moments, you will be asked:
CLEAR MEMORY?
Press the LOAD key. You will be asked:
ARE YOU SURE?
Press the 1 key. The PCM70 will briefly flash:
CLEARING MEMORY
and then load program 0.0. All registers will be erased and all control
parameters will be returned to factory presets.

I have cc'd this message to our tech support staff (Greg Hogan, Jim
Ciardelli and Brian Wood). They will respond [please, Greg, Jim, Brian]
with any other ideas.

Barbara Johnstone
Customer Service Manager
Lexicon, Inc.