Reread this, if only your light bulbs turn on, and not the button lights or no other sounds, it's most likely a fuse popped or PS is straight dead. If PS, you can check for popped capacitors. My cap repair job on old one didn't work, and I never found a used working one. Had to make my own.
The light bulbs inside your sg50 are connected straight to wall outlet essentially, they don't use the Power Supply. So don't assume you actually have power unless other things work, ie screen has power or boards inside (coin comparitor, etc) light up.