Sven, welcome to the forum and to the new world of owning pinball machines!
The first machine I ever owned was a Williams Swinger, which was the 2-player version of Funfest. I know it's a little intimidating when one first looks inside the cabinets, but it's really not rocket science and I'm sure you'll learn quickly.
The jet bumpers and the 2 slingshots run off a different power circuit than the flippers and the rest of the playfield. Williams used a bridge rectifier and ripple-smoothing capacitor to deliver about 26 Volts DC to the bumpers and slingshots, whereas the rest of the machine operates off of AC power. The part of the schematic that you circled in red is the DC rectified power subsection. Most likely, one of those components of the DC rectification circuit is shorted or blown.
It sounds like you checked the 4 fuses in the main fuse block in the front of the cabinet, but there is another 10-A fuse just for the rectifier, located on the gray-painted underside of the playfield, probably towards the upper middle on the right side. Locate that fuse and pull it out and check for continuity with a multimeter. While the fuse is out, clean the fuse holder terminals with a little sand paper. If the fuse is good, then look to the bridge rectifier next and try to test it with a multimeter to look for voltage from the output terminals marked (not the ones marked with a tiny sine wave). Lastly, it's possible the capacitor could be blown, although the fuse and rectifier are the more likely culprits.
Lee
