If your V50 suddenly shows strange characters on the display and it sounds strange (drums together with a normal sound), it is very likely that your internal battery is dead. All the internal settings and internal sounds will get corrupt when the battery is dead.



So now we have to change the battery. The battery is a normal CR2032 buttoncell available at your local electronics-shop. Sadly the soldered battery in the V50 was not available at my local shop (Murphy's law), so i decided to use another type with soldering-pins on it.
At first we have to open the keyboard. I put it on a soft blanket and some bubble-packaging-foil to protect the cover.

Unscrew the screws on all sides: