Mega Drive 1 - Switchless Mod
UPDATE - thanks to dosucul who pointed this out to me, there is an alternative I didn't know about. Have a look!
Righto, you've seen the excellent Switchless Saturn Mod, made possible thanks to Seb. I love it, it's fantastic so I wanted to use it to mod another console. I'd just bought a couple of Mega Drives so thought I would see if I could adapt it for them. The good news - one of the consoles was very very easy, the bad news - one was more difficult but I got there eventually.
First a recap on how the MD1 jumpers work. The photo below shows JP2 and JP4 linked up, this is PAL console.
JP1 and JP2 controls the language of the console (GND for Japanese, +5v for English) - the 2 points on the left (highlighted in green) are linked on the underside of the motherboard.
JP3 and JP4 controls the video mode (GND for PAL, +5v for NTSC) - again the 2 points on the left (highlighted in blue) are linked on the underside of the motherboard.
Assuming you've built the circuit and programmed the 16F630 PIC from the Saturn guide here's how you can adapt it to control your Mega Drives settings.
Video Mode:
The wire that would normally control the video mode (the one that goes to
pin 79 of the video chip) on the Saturn needs to connect to either of the points
highlighted in blue above (the left side of JP3/JP4)
Language Select:
The wire that would normally connect to JP10 on the Saturn motherboard needs to
be connected to either of the points highlighted in green above (the left side
of JP1/JP2)
For power you can use use any of the GND and +5v points on the motherboard, for example JP1 for GND and JP2 for +5v.
| Mega Drive | ||
| Language | Video Mode | |
| 16F630 output leg | 9 | 12 |
| Connects to | JP 1/2 | JP 3/4 |
| EUR | +5v | GND |
| JPN | GND | +5v |
| USA | +5v | +5v |
And now the easy console first!
Look at the reset switch and this is where a multimeter with a continuity tester
comes in handy. This motherboard had IC BD M5 PAL written on it and had
the same kind of reset button as the Saturn - when pressed it sends a GND signal
which resets the console.
The 2 points of the switch highlighted in Pink above are linked to ground. When the reset button is pressed it links the 2 points of the switch highlighted in Blue to ground, the ground signal is then sent along the single point highlighted in Blue.
You need to cut the trace shown in Red in the photo, solder the Button wire from the 16F630 circuit to the point labelled in the photo, and the Reset wire to the clearly labelled point in the photo.
That's it, a Mega Drive where you can the region and video mode exactly the same as the Saturn, it behaves in exactly the same way allowing you to select between EUR/USA/JPN by holding the reset button and releasing it on a certain colour Green/Orange/Red. You can alter the video mode by holding Reset for about 1 second, and you can reset by quickly pressing and releasing the reset button.
