When this Yamaha SY77 came into the shop, its sound programs were gone.
In the display, their names were all nonsensical character strings.
The SY77 had lost the data it needs to construct sounds and display
This is often caused by a low internal battery. Voltage from the
battery holds the sound data in RAM when the SY77 is turned off.
You can restore the original factory sounds by following these
Yamaha SY77 reset instructions
but you can't get back any custom sounds, settings, or sequences
unless you've backed them up using MIDI or the onboard floppy disk.
And unless you install a fresh internal battery, you'll have to
reload the factory sounds again and again.