I got the following procedure from ML to reset the No. 390S:
1) Turn unit OFF (not standby).
2) Press and hold the front panel PAUSE button.
3) Continue holding PAUSE button while turning power ON.
4) The unit will display START UP, CODE XXXX, NEW DATA, DEFAULTS on the front panel display. Release the PAUSE button when the display stops changing.
1) Turn unit OFF (not standby).
2) Press and hold the front panel PAUSE button.
3) Continue holding PAUSE button while turning power ON.
4) The unit will display START UP, CODE XXXX, NEW DATA, DEFAULTS on the front panel display. Release the PAUSE button when the display stops changing.