50Hz 60Hz Switch (Sega Saturn)
The Sega Saturn has various revisions so performing the mod depends on version.
As with most consoles to do a frequency mod the principle is to send a specific pin to ground or 5V.
Every revision of the console can be done/reverse engineered from the same point if needed.
The video mode is controlled by the 160 pin VDP2 315-5690 (pin 79 Video Mode). This pin also joins to the CXA1645M video encoder (pin 7 NPIN)
Sending this pin to ground outputs 50Hz. Sending it to 5V outputs 60Hz.
Some revisions already have this pin wired to a blank switch pad at the rear of the console, and others have a test point and jumpers.
On some versions it appears Sega intended to even have a switch in the battery compartment door at the rear, specifically for frequency switching.
If you have a version with the empty switch pads all you need to do is add back a switch that connects the middle and right pad together for 60Hz and left open for 50Hz.
Ground is 50Hz, and 5V is 60Hz.
I solder the cage of the switch to the ground plane by exposing some of it. This anchors the switch solid to the PCB.
You can also close the back door without issue. Notice I trim the black plastic surround inside by removing the bar that would otherwise run past the switch.
Sliding the switch to the right outputs 60Hz, sliding it to the left outputs 50Hz.
Some revisions have two test pads next to each other.
JP1 goes to 5V on one side. and the other side joins to the JP2.
JP2 goes to ground one side, and the other side joins to JP1.
From understanding this and looking at it, you can deduce that the shared pad where both JP1 and JP2 meet is the Video Mode pad that goes to the VDP2 and the CXA1645M video encoder (pin 7 NPIN).
Remove both resistors from JP1 and JP2 if present, and if there is a trace joining both pads of JP1 or both pads of JP2, cut those traces.
Now install a 10k or similar resistor on JP2 to pull the Video Mode pad to ground.
Finally, solder a switch with one side to ground, one side to 5V, and the middle common pin of the switch to the Video Mode pad (the one where JP1 and JP2 join together, or pin 79 of VDP2, or pin 7 of CXA1645M).
Switching the switch to the side with 5V outputs 60Hz. Setting it to the side with ground outputs 50Hz.