circuits

Can any of you point me in the direction of any resources that can help me understand how to test the circuits of a bass with an active EQ? I snagged a really clean Ibanez SRX300 off ebay for only 30 bucks, and it's in fantastic shape except that the electronics are not functioning.

Hi! I today bought a Sweet 25.1 Combo. In the Manual they wrote about Protection circuits against HF Oscillation and so on. But they only described these circuits for the Sweet 15.2 (One Manual for all). Does my 25.1 not have and/or need these?