Pre amp doesn't work on kicker

I just bought a 100watt kicker from a friend. He said the amp works fine.
The only problem he has with it is the pre amp doesn't work. When you flip the switch to turn on the pre amp it loses all audio. Any ideas to what might be wrong?

 

Thanks for the advice I will look into the transistor and the switch. Would it be worth fixing the pre amp or will it just pick up more noise? I guess I should have asked that question first.

 

It depends on what truck I'm in. The normal truck drive I pick up a little noise.
I think I'm going to fix it. I plan on working on it myself. I only paid 30 for it I don't want to
pay someone another 30 or more to fix it. Thanks again for the help

 

I found 2 transistors both are the same number s7502. The one looks like it may have been replaced. The leads 3 leads from the transistor are soldered to 3 leads coming out of the board. The other transistor is soldered to the board. I don't think that was the right way to replace it. But I'm sure it was easier than pulling the board out.

 

I plugged the amp in and the flipped the pre amp switch on and the light came on showing the pre amp on. So it may be the transistor.