Ensoniq ESQ-1 with display not working

A question from our email:
I just got in this Ensoniq ESQ 1 (Metal). It turns on but there’s no display. If I push any of the buttons a character comes on the display. It plays a piano patch. I change the battery. Can this keyboard be saved?

My answer:
If the display shows those characters when buttons are pushed, that means two things:
(1) The display itself works, and
(2) It is not communicating with the main board.
(This applies to many different Ensoniq keyboards, by the way.) So the problem may be the cabling that connects the two, or the connections for that cabling. Make sure the wiring is plugged correctly, and unplugging and replugging often helps, as it can improve the connection.

If the problem persists, it is likely an issue on the main board.

Changing the battery won’t help at all. On most synths, the battery serves only one purpose: to store data when the keyboard is turned off. As long as the keyboard is on, the battery does nothing - you could even remove it completely and it would have no effect.