Crispy power switch on a JDM Pioneer SA-8800 (SA-7500 in the US)
Over time, with these old machines, the power switch contacts get pitted and a little burnt from having full mains power (120v US) flowing through them at power-on. The factory did try to limit this by adding a small ceramic disc capacitor as a snubber (arc suppression). This only works so well and, after 40+ years, the switch contacts get carbon-fouled and even pitted. If they get really bad, they'll buzz at start up as the carbon interferes with the contact surfaces.
So, every restoration I do get the power switch pulled and cleaned up. This means the switch body comes apart and everything inside gets overhauled.
You can see in the above pics that the contact pads and contact bars are lightly pitted from years of use. Luckily, these are not plated so they can be burnished and made fairly smooth again.
The pads are not removeable so they need to be lightly sanded in place, which is not easy. Best effort. I forgot to take a picture of the bars, but they were sanded with 2000 grit sandpaper to remove the tarnish and pitting.
Back together and a new capacitor across the terminal. It has almost 2 times the voltage capacity, but is smaller than the 40+ year old original. A 120 ohm resistor is also added to one leg of the connection to aid the arc suppression of the cap. Should be good for another 40 years.