Diagnosing a Pioneer SX-535: High DC Voltage at Speaker Terminals!

What tools do I use? https://youtu.be/MLK649c1_fM This SX-535 had extremely high DC voltage at its speaker terminals. The source of the issue was the power amplifier board. I thought at first it might be the differential pair transistors, but it was actually the bias transistors that were causing the issues. Replacing the old 2SC1318's with modern KSC2690's solved the problem! I had seen very similar things happen with the Pioneer SX-636 in the past, which has a very similar power amplifier design.