Recently I got a A1200 NTSC Board. It is running @60Hz. You can set the speed of the Amiga by hitting both mouse buttons at Power Up. But I want to make it permanent to 50Hz because I am living in germany and some games need 50Hz.
I done some 50/60Hz switches for the Amiga CD32 Unit and it is similar.
You have to find R203 downunder and use a a switch. didn’t want to make a hole into the case of the Amiga. Therefore I am using the switch of the RF-Unit. I set it permantly to Channel 2 (but I didn’t think I will never use the RF-Output).
Here are some pics
you have to cut two circuits running to the switch. And it is free for 50/60Hz usage.