Kawai K5 patch saving issues

Hi everybody,

I recently bought a Kawai K5 synth (circa 1987) that has the following issue: when saving a single patch on some slots, the saving process fails and the screen displays a “Verify Error” message.

This only happens on certain slots, for instance, on bank A, I can save patches on all positions, except 5, 6 and 7. On bank B, the faulty ones are 1, 2 and 3. MIDI dumps on these position do not work either.

Memory Protect is off. I have replaced the lithium battery and soldered it properly, which did not solve the problem. I have ordered a new EPROM with the internal software update.

Any idea what would cause this issue?

Big thanks for your help!