Siel DK 80 no sound

Hi,
I bought this second-hand Siel DK80 synth almost 15 years ago, and it worked very well even 6 years ago because I used it for my EP at the time. I reconnected it a little while ago and to my surprise no sound comes out…
My preset selector is stuck on preset 5, and I can’t press “enter”.
I’ve read a lot about the 3V lithium battery that can fail. But would it cause this kind of “no sound” problem?
I’d like to try changing the battery first, and am able to open it and desolder/solder.
If it doesn’t come from the battery, what steps should I take to find the fault?
Thank you and I really hope to have an answer as it’s very difficult to find information on this synth!
Have a nice day :slight_smile: