Hi, I know this is a long shot and the correct answer is take it to a tech but I'm going to ask anyway. I recently bought an older USA Crate powered PA head. There's a solid thump when it turns on and the mixer portion works fine, all fuses are good, but there is no output to the speakers. The typical diagnosis for this symptom is old filter caps that need replacing. I have basic soldering skills and a multimeter. Can anyone point me to a good tutorial on how to do this? Or is the answer still play it safe and take it to a pro?