plays for short time and goes off

My yamaha keyboard plays for shot time and stops to produce sound even when power is on. To make it sound a gain I had to hit one of the speakers wire on one of the transistor. That left speaker as well doesnot work. This has been disturbing for the last 2 weeks. What could be the problem and how do I fix it?

Here is the picture of the transistor that I rubb on. Another thing is that, the switch as well does not work, when I plug in the dapter the power goes direct.