Buttons like "Sequencer Start/Stop" or category buttons require hard pressure or do not work at all.
Ultimate Guide to the Korg M50 Service Manual: Maintenance, Schematics, and Repair korg m50 service manual
Hidden diagnostic routines built into the firmware to test hardware without opening the case. 2. Navigating the M50 Test Mode (Diagnostics) korg m50 service manual
: Steps for replacing the CR2032 lithium battery that preserves user data and system settings. korg m50 service manual