Help for my Roland U-20!

Just got a Roland U-20 and the display act strange when you are trying to change the setting using the cursor button. It display weird characters (#%##). Because of this, majority of the keys are not functioning. Is it a mainboard problem or what? Please reply.

Thanks.

Try replacing the internal battery..

I've tried to remove the battery and measured the voltage. It has a pretty descent charge of about 2.8V out of the original 3V. What next?