Quite an easy mod to do, and essential if you use any one of the many ways to play imports on your Sega Saturn, if you’ve done the single switch region mod, then you can get power from that board (top row of diagram for +5v, 4th row for GND), if not, then you can get power from the underside of the motherboard from the pins for the PSU, if you want, you can use a multimeter to find an alternative 5v and GND, there’s lots of them.
You’ll need a Single Pole/Double Throw switch and some thin wire, solder the +5v wire to one end contact of the switch, and the GND wire to the other end contact, leaving the middle contact free for the wire needed to send the signal to the graphics chip.
Most other guides for the 50/60Hz switch say to cut a trace on the motherboard and solder a wire to it etc. This can be quite messy, mmmonkey prefers to find the graphics chip (it’s the only 160 pin chip on the motherboard apparently, and labelled IC14), on my VA9 motherboard, the chip has 315-5964 printed on it. If your board isn’t a VA9, then check Mameworld for info on finding the right chip. Once you’ve found the correct chip, you’ll need to separate pin 79 from the motherboard, mmmonkey heated the solder then used a very sharp thin scalpel blade to pull it upwards away from the motherboard and then straightened it with a pair of small pliers.
Now you’ve got the leg lifted up, put some insulating tape underneath it, and melt a little bit of solder onto the leg ready to solder the wire on. Prepare the wire by tinning it, and cutting the exposed wire very short, then simply hold it onto the leg and touch it quickly with your soldering iron to join the wire and leg together.
Make sure you secure the wire down properly, you don’t want a slight tug on the wire pulling the leg off of the chip! Put some insulating tape over the wire/leg join, then tape the wire down along the motherboard, plan a route so it comes out where the switch is/will be mounted. mmmonkey mounted the switch on the door to the Battery/VCD Card compartment.
I got this info from the guide at Mameworld, but I think that site is long gone now :-( they had a few interesting things on there.
I did have a bit here saying to cut the trace leading to pin 79 of IC14 instead of lifting the leg. This doesn’t work on all motherboard versions though. So I would recommend lifting leg 79 and soldering to the leg still.