Korg M1 - Screeching, echo on output

I’ve got a Korg M1 that needs some love.
I’ve changed the coin cell battery as it was 3.0v for a new one.
The power rails are OK at 5v and +/- 11.8v.

I’ve uploaded the midi file via sysex librarian and get the correct names for the presets. I changed the buffer settings to 256.

However, the sounds are really distorted with screeching, ring and echo. It’s as though all the effects have all been switched on. I went into the settings and turned all the effects off and get a reasonably clean sound, but a short while later they are back again. I can hear the original sound in the background if I keep pressing keys on the keyboard.

Anybody know what this could be?

I’ve just installed the RAM chips and as suspected, these are the cause of the problems.

Pictures show new M5M4464AL-12 RAM chips installed.

Sound is now clean and back to the classic original sound!