I've been known to get a little MacGyvery from time to time yes
So I had to tear it back apart, the Deoxit treatment I gave the stereo mode switch fell away and was getting very little bass on stereo and just a bunch of popping on stereo wide.
Pulled the stereo switch off the board and opened her up for a deep clean. That cleared that up, but I still hear crackling on the line. I knew that a dirty aux switch had given me trouble like this before so I pulled that off as well and did a disassemble/deep clean.
Nope. The crackling was still present. Next up: loudness switch.
Nopers! So, I decided to try cleaning the mode switch, since it was the only other switch in the audio path that I hadn't cleaned.
Nope again! Up to this point the only place I could affect the crackling was at the balance and volume pots, but that occurred when I turned them as well, and I had already pulled those apart and gave them a deep clean, so I was suspicious the pots were just really worn out, although the carbon tracks looked fine.
After removing and disassembling four switches and two pots, and resoldering the bass and treble pots (bass pot did have solder cracks at the board), I could
still hear crackling. Although I applied Deoxit to the switches. So, I ran over to Guitar Center and bought some Faderlube for the pots, and doused them in that. Voila, no more scratching on the pots!
But the crackling. It remained. And no it wasn't the headphone jack, cleaned that too!
One more thing I did was replace both amp chips. I wasn't getting strong bass output and was worried that there was an imbalance in the amp chips. At least one of them had been replaced at some point in the past with an ECG1606. I also replaced what SHOULD be an 11V zener at the spot that gave me problems on another board. There was a tiny burn spot and was getting 14.3V instead of 11, and although it still worked, I popped in a new one and got a better reading of 11.5V.
But the crackling, where was it? I had cleaned and replaced just about everything that made sense, and so I started doing a wiggle test and more visual inspection. The problem turned out to be some crud left over from resoldering the pots, some solder flecks suspended in old flux had gotten onto the points where the output cable runs from the amp board to between the volume and balance pots on the control board. Once I cleaned that out of there I was clean as a whistle and thumping properly