There are a couple of different mods out there to make your Mega Drive work with all different regions – there’s a switchless mod that changes region by holding the reset button which is quite nice, but require a chip and new LED, so I won’t cover that one here.
There’s also another mod with one switch for region (US, EU or Japan) and another switch for frequency (50Hz or 60Hz) – but since all US and JP-games are made for 60Hz and all EU games are made for 50Hz, I’ve never really understood why you would want so many options.
This is the easiest and most optimal mod if you ask me: https://mdpal60.net/regionmod
In this mod, you add only one three point switch to select between US 60Hz, JP 60Hz or EU 50Hz. The switch is called Single Pole Triple Throw (SPTT) with On – Off – On. This means that it has one single row of connection points and can be put into three different states. You can use a Double or Triple pole switch as well, just be sure to use only one row if you do. And also, the type of switch on my picture needs to be soldered quite quick – if you heat it up too much it can melt together and short itself inside. So order a couple of extra switches to have as backup – and test them with multimeter after you’re done.
Also note that this mod doesn’t add an extra xtal, so you won’t get exactly 60Hz if you have a PAL machine (and not exactly 50Hz if you have a US or JP-machine). This is not noticeable and isn’t a problem for most people (me included) but some upscalers can have problems and speed runners need to have it exact. You can google Mega Drive / Genesis Dual Frequency Oscillator (or DFO) if you want to know more.
When you’re at it – you could also take a moment to clean the connector. Get the dust out with a needle, then take a piece of clean printer paper, fold it a couple of times and drench it in isopropyl alcohol, then run it press it down the connector a couple of times, until no marks are left on the paper.
If you want to be able to play Japanese games on your console without an adapter, you will also need to cut off some plastic in the shell. I used a Dremel to do this on mine.
