My MegaCD is region free!

...and speaks japanese :-)

My european Mega CD

I finally received my lot of EPROMs (ST M27C1024) pre-programmed with a modified region free Japanese Mega CD bios, thanks to l_oliveira at assemblergames forum for the hacking!

European VS Japanese BIOS screen

Here is how I installed the new bios...
These hacked bios images let the user replace the official Mega CD bios, removing all the region locks normally present in the console (the Mega/Sega CD starts only with a Mega Drive/Genesis of the same region, and only starts same region discs). Unfortunately this mod is not a trivial one: the ROM chip with the original bios must be disconnected from the board or somehow disabled. One way to get rid of it is completely desolder the old ROM, put a socket on its place and put the new EPROM (which, of course, must be programmed with the byteswapped bios image) inside of it. While this solution is the cleanest, it's also hard to perform without good equipment, so I decided to take another route: keep the original ROM in place and add a (internal, i don't like cutting holes in my consoles) switch to select the new bios (which can be fitted directly on a socket soldered on top of the original ROM! Piggybacking!).

The two chips are connected together (soldered) pin-by-pin (except PIN2, Chip Select, which must be connected as the figure shows, after being disconnected from the original circuit board pin hole by cutting it).

While I did this, I also took the time to completely replace all the capacitors inside the console, as the Mega CD Mark1 is famous for having faulty capacitors that cause instability and CD reading glitches. Now it works (almost) like new (and reads CD-Rs too)!

Why did I choose a Japanese version instead of the American or European version? Well, it's  not just because it looks cooler: some Japanese games rely on routines present only in this version, making them unplayable when a different region bios is installed, even if the region lock is removed. Have a look at the forum thread linked at the top for more infos.