Yamaha PortaSound PSS-780 Operating Manual page 22

A) Single Finger Chords
re
C Major (C)
C Minor (Cm)
C Seventh (C7)
C Minor Seventh (Cm7)
Note:
In general, you should release the keys completely, lifting
your fingers off the keyboard, to change to a different
chord with the Single Finger Chord function. Otherwise,
you may not be able to obtain the intended type of chord.
For example, if you want to change from G major to A
major and do not release the G key completely before
pressing A, you will get an A seventh chord instead of the
A major chord you wanted.
SSS SSS =
19