The serial number is typically found on a black sticker located on the rear panel of the synthesizer, near the audio and MIDI connectors.
Older units with lower serial numbers may require specific EPROM chips if you are looking to upgrade to later OS versions, such as those found in the . Why the Serial Number Matters Korg M1 Serial Number
If you still have the original box, the serial number was originally printed on a label on the exterior. The serial number is typically found on a