Rebuilding a Pioneer SA-7500 II

A few months ago I purchased a Pioneer SA-7500 II from a Friend here with the intention of refreshing it. I bought a recap kit and found the service manual online, but am a little lost about test voltages from a schematic. My troubleshooting experience up to this point had been on Bottlehead amps that provide very specific instructions for testing.

Does anyone have a preferred primer for how to interpret a schematic to determine values to test after rebuilding an amp to see if it’s working properly? And is anyone aware of a guide for recapping a SA-7500 II? I’ve seen something approaching a guide for a 7500, but not the II variant.

 

A common way to prevent magic smoke is to use a variac and slowly turn up the A/C input voltage, probing around in the power supply section to make things are behaving more or less right (e.g., ratio of voltages is right given input voltage). Then go up in voltage from there and confirm the rail voltages stay in tolerance. Bear in mind that diodes don’t turn on until they get about 0.7v, so need to get at least that much into the bridge rectifier to check filtering, etc. While under voltage, gain stages of the circuit won’t work properly, but you usually you won’t damage anything.

Most Pioneer amp schematics I’ve seen list operating voltages at key test points (usually around the pins of the transistors). Note that there is some wiggle room (say 10%) around many of these. The M22 manual has them listed on the board-layout schematic as well, which makes life easier.

Once at full voltage, perform the adjustment with trimpots as specified in the manual, confirm the lack of large DC on the input and output terminals (a few mV on output is OK) and then test on some (cheaper) gear or into a dummy load.