Why does my HK onyx 3 distort and lose sound?

Hi,

I have a HK onyx 3 BT (there was no onyx 3 subject thus writing to onyx 2 subject) and used it for couple of months when I bought first. It was not used for a while and when I started to use again I came across a sound cut off problem during playing. But when I keep pushing any button it continues to sound properly. Should I change buttons card (board) or is there anyone had same problem?

Thanks