Here is the hard reset procedure for the Kurzweil Mark 10/110/150:

1. Turn the unit off

2. Hold down the SWING/JAZZ WALTZ and START/STOP buttons

3. Turn the unit ON and swiftly press and hold the TRACK 1 button (while continuing to hold the other 2 buttons)

4. Hold these buttons for 5 seconds and then release all 3 buttons.

5. The display should now read 000

6. Press the UP arrow button until the display reads 003

7. Press and release the VARIATION button

8. After a few seconds, the CHORD HOLD LED should flash, indicating the test has finished.

9. Power the unit off and back on, your Kurzweil is now reset.