We had two JL Fathom f113 subs come into our shop a few months ago. The customer had blown both w7 13" woofers and there is damage on one of the amp boards. The quote for repair for the subs was nearly 2/3 the original cost of the subs so the customer just left them here for us to deal with, so I took them home to try and repair. I was able to get parts for rebuilding the woofers from the guys at Lord of Bass online. I have both woofers rebuilt and installed and amazingly I have one working sub! Unfortunately the other sub had a loud whine as soon as I powered it on. The noise continued after I put it into standby and only stopped after the caps drained. I tested the transistors on the output and 5 out of the 8 were shorted. This is where my knowledge of trouble shooting amps ends sadly. If I can get any advice on how to move forward, I would be most appreciative. Mostly I need to know how to tell if the drive boards are damaged before I install new transistors. I don't have an oscilloscope.
