The Megadrive is one of my favourite consoles. I bought one brand new when they came out, and still have my original boxed console. I have a modded PAL model with switches to switch between 50 HZ, 60 HZ, US, EU & JAP modes. However I have always wanted a Japanese model because in my opinion it has a much more appealing look to it. On a recent trip to Japan I picked up a working Japanese model. I want to mod this one as well, but thought I would try a switchless mod for the first time. The model of my console is ICBD M5 837-6656. There is plenty of good information available online to perform this mod. I referred to http://www.mmmonkey.co.uk/console/sega/md1-switchless.htm for general information and this site (in French) for information about my particular model https://dragoncity17.wordpress.com/2014/12/23/megadrive-1-switchless/. Scroll down the page a bit to find it.
Essentially the mod comprises of a programmed 16F630 PIC chip to use the reset button to switch between different modes. You can buy kits for this mod online which are handy, however relatively expensive for the cost of components. If you have access to PIC programmers and can solder the cost will be under $5.
After programming the PIC chip, I constructed the circuit from http://www.mmmonkey.co.uk/console/sega/saturn-ultimate.htm. Note that the mod started out for the Saturn.
I won’t rewrite the source documentation – I will share some experience below.
Upon opening the console, be mindful of the LED wiring back to the motherboard. Carefully remove the plug on the led legs by sliding it down.
Referring to instructions from the French website listed above, look for the jumpers which need to be cut. On some models like mine there might be a cap across one of the jumpers. This can be simply removed.
The French site pictures which traces need to be cut, and where to attach the circuit/ chip to points on the Megadrive.
Whenever doing a mod like this I install it quickly, just to make sure it works before making it neat.
Now the wires have been neatened up, and double sided tape is used to hold the circuit in place. Some modders like to install mods like this without a mounting board. There is nothing wrong with this, I like to use strip board though.
The existing red LED will need to be removed from the top case. This will require some plastic to be drilled or scraped away from the underside of the LED.
This Megadrive has a physical lever to stop non Japanese cartridges being used. To remove this, take the screw out which attaches the lever to the case, Gentley prise the lever off the power switch, and break the lever away from the case.
When installing the new tri colour LED, use hot glue to hold in place.
After putting everything back together, the mod works great. Essentially hold the reset button down for several seconds, with the LED colour cycling through to pick a different region. Then once you have set on the right region, holding down for a shorter period of time until the LED flicks off will allow switch between 50 – 60 Hz. Finally a momentary reset button press will perform a reset as normal.