Nintendo SNES / Super Famicom

The second major console from Nintendo (Super Famicom in Japan, Super Nintendo in Europe and the USA), is the successor of the Famicom or Nintendo Entertainment System. It uses roughly the same hardware architecture as its predecessor, yet slightly improved.

Points to note:
 * If this guide talks about replacing one of the bigger chips (PPU/CPU/WRAM), the chip can be replaced with any version of that chip. Multiple versions of the CPU, PPU1, PPU2, and WRAM chips have been made and these can be mixed and matched without issues. None of these chips are still in production so they will have to be salvaged from a donating device.
 * It helps tremendously if you can get your hands on a SNES Burn-In Test Cart. Unofficial ones can be bought through various channels like Amazon or AliExpress for cheap. They can test various hardware issues.
 * The power smoothing capacitor inside the device holds quite a charge after the device has been turned off (because the power switch is positioned between the rectifier and caps and the rest of the device). Make sure you discharge this capacitor before you work on the machine's insides. This can be done by turning on the device using the power switch while there is no power supply plugged in. The power LED will flash shortly if you do this.
 * There are basically two major architectures for the device. The multi-chip, and the single-chip (1CHIP) versions. The latter is the latest version and combines multiple chips (CPU and PPU) into one. The number printed on the PCB should clearly show if it's a 1CHIP version.

Detailed technical sources
Check out Console5 TechWiki on more details on the SNES, including full schematics and board layouts.