Ensoniq MR76 - Not start and displays black squares

I’m having a problem with my MR76.

It was playing and suddenly it froze and the screen went black.

I turned it off and on again, but when I turn it on it gets stuck and the screen only displays black squares as shown in the attached image.

Has anyone else experienced this and have any advice on how to solve it?

Note: It doesn’t have an internal battery and I’ve already done a hard reset and a soft reset and it didn’t work.

Thank you!