Kawai K1 problem

Hi, I have one question please. I bought a used Kawai K1. Unfortunately, after plugging in, I found out that there is no sound. The headphones make a noise when plugged in, I think it’s not in the output. I also tried other audio outputs. After connecting the midi, the computer transmits data (the light is on) but again without sound. It doesn’t even work when pressing the MIDI IN keyboard (the light on the converter doesn’t light up). The recording is not recorded on the sequencer in the computer. I am kindly asking for advice, information, what it could be. This machine does not have LOCALL OFF. The display lights up normally and the names of the sounds are legible, etc. Could it be the battery? But why can’t Kawai be used as a master keyboard in that case. Thank you in advance.

First to check - open it up and see if the cable between the volume control and the main board accidentally has been disconnected … that’ll make the entire output go “dead”. - ie all else seems to work except no output what so ever.