This isn't going to be as much of a log, but I had a centipede on the bench with really quiet and distorted sound, it ended up just being a bad LM324 preamp at K10. The way I troubleshooted this one was literally by stacking a known good one right on top of the bad one. I did a little video to showcase exactly what I am talking about:

Edit: just to emphasize how common of a failure this is, I worked on 8 centipede boards today, 3 out of the 8 had a bad/failing LM324. It's good to have a large quantity of these things lying around if you repair boards...