Hi everyone, since i’m new member of the forum i would like to share one of my Project that keeps me busy since december 2013, i think the title and the explains everything but here is my story. I’ve met some very talented guy over spanish forums nickname Giacomo Agostin, he is as intersted as me about sega mega tech but also is more talented than me on electronics . He is the one who figured out this beautiful mod. I dont have any knowledge about designing circuits using kicad or similar software and i dont know anything about how 74hc/ls buffers are working, i still havent completed mod but i decided to share it here maybe actual design can change in the future. I’m going to send it fabrication soon and it can be useful for others. Giacomo, thanks for guiding me about it and sharing your designs with us. The six button mod is a little bit hard to explain it. Basically you need to take off 5 IC from the Mega-Tech board and solder sockets instead of them. Then you must plug a pair of PCBs over those sockets. The signals that Mega-Tech uses to receive the buttons goes through the ICs and we need to mix them from the ones coming from the Megadrive pads using AND gates and a few buffers to prevent any damage to the board. Here you have the PCB of the final boards (and another one that I designed for another project). As you saw on the pictures I posted on the forum, the 6 button mod is made on prototype board and it´s a little different from the PCB on KiCad (I didn´t tested this one yet but I suppose It will work perfectly). If you want to make this mod, be very carefully taking off the ICs and replacing them with sockets. I had some troubles to clean the pads to insert sockets. The ICs from Mega-Tech board that you have to take of are all in line. An 74LS257, 74LS244, 74LS08 from the left side and 74LS257 and 74LS32 from the right side. Between them is an 74LS32 that you have to leave on its place. As you can see on these pictures, I used some pin arrays and more sockets to raise the board. The buffers used in this board are 74LS125, but the final board will use 74LS244 buffers. I'm also attached kicad design file and files converted to gerber format.
