I've installed the FM upgrade board 4 times now into a few different SMS NTSC consoles now and something that I tend to always forget, is that the official instructions for installing the board has a few mistakes in it. One of those mistakes is a pretty big one that I've mentioned to Tim Worthington a few times but it never seems to get fixed in his guide. That step is regarding the process for getting the region switch working on NTSC consoles. Now the steps listed I'm sure are accurate for PAL versions of the console, but 3 different model 1 and one model 2 unit I've installed the kit into all required the same thing to get it working.

The specific step to install the region switch wire states to solder a wire from the IORQ pin off the FM board and to isolate and solder the same signal pin on the 2516 IC chip in the console. This chip is the IO Gate array IC btw. The docs state this is pin 19 on that IC and that is a correct statement. However, removing this pin from circuit on the NTSC consoles will prevent the SMS from booting at all. Just a black screen when powering on the console. Attaching the region switch wire to that pin while isolate does nothing.

The pin you want to attach to instead on that IC is actually Pin 23. It is listed as the KillGa pin and I assume has something to do with a halt or reset. In some models of the SMS pin 23 isn't attached to anything. But on the NTSC systems it is part of the circuit. So, you have to either cut the trace to this pin or lift the pin from the board to isolate it and then install the IORQ wire from the FM board to pin 23. This will correctly allow switching the region on the SMS. The region switch isn't dynamic so you have to either reset the game after switching, or power the SMS off and then back on for the region switch setting to take effect. Here is a picture of the wire I'm talking about attached to a lifted pin23 off the IC I did the other night as an example.

Here is the IORQ pad the other end of the wire attaches to on the current and latest version of the FM board upgrades. Depending on the version of the FM you have, this pad has changed places but it is always labeled the same. In the pic below is the yellow wire soldered on the upper left section.

So if you ever install one of these or possibly have one installed and hadn't gotten the region switching working on your NTSC console, now you know why and how to correct for it.

BTW the switch is advised because it allows you to select between US/PSG audio, US/FM audio, and JPN/FM audio settings. There are 2 games known that require the JPN/FM setting in order for them to work with the main one being Wonder Boy III: The Dragon's Trap here in the US (Wonder Boy II in JPN).