does not come on

Several possibilities exist for this. The first is that the power supply itself is bad. These have a high failure rate now because of the age. The other possibility is that the power jack or power switch is loose, and needs the solder reflowed. The solder on these boards is weak from age, most units I work on all need reflow. There are also a few capacitors on these that need replaced. This usually won't cause it to completely be dead though, most likely you would see partial static, blank screen, or color bars. Make sure the cartridge slot and cartridges are clean. Nothing more than rubbing alcohol is needed to clean them.