If you’ve modded your PAL Mega Drive for 60hz, and aren’t able to use an RGB cable to get a colour image, here’s an alternative for you, allowing you to use a non-RGB cable as your console will output a PAL60 signal.
I first saw this years ago but never tried it, then found it again on this excellent guide by Zipplet which goes into detail explaining why you get a black and white picture in 60hz mode.
Summary of Components
I bought all of that from bitsbox.co.uk, some of the parts are slightly different, but they worked perfectly for me.
Here’s a copy of the diagram from Zipplet (permission given to host here too)
I tried 2 different methods for this, one using a piece of stripboard, the other soldering directly onto the chip legs. Whichever method you go for, there’s a couple of things you have to do first, you need to locate the video chip (CXA1145), it’s under the metal heatsink, identify Leg 1 and then count along to Leg 7. Once you’ve found it, cut the trace that’s leading up to it (I usually use a craft knife/scalpel to put two small cuts in, then dig out the bit of trace inbetween the cuts, look for a bit to cut or cut in a direction away from other traces etc so that you don’t damage or cut anything else). Now you need to solder a link wire from Leg 1 (which is Ground) to Leg 7.
For the next step, I used a pair of side cutters to carefully snip legs 5 and 6, then pulled them away from the motherboard and straightened them out.
Circuit Board Method
For my first attempt, I designed a small board on a piece of stripboard/veroboard. Lets start by making a single break in a copper track
I’m hoping the next lot of photos are easy to follow as there isn’t a diagram yet! Here’s the capacitors soldered into place.
And the crystal soldered in
The last component is the resistor.
Inspired by Zipplets board, I used the cut off legs of some off the components to link up the board to Legs 5 and 6. The white wire is what I’m going to use for Ground.
I put a piece of double sided foam tape on the Mega Drive motherboard and stuck this board in place and soldered the links to Legs 5 and 6. The white wire is soldered to the nearest ground point, this could be Leg 1, or a nearby component which is linked to it.
Solder Directly to Legs
Then I decided to give it another go, soldering directly to the relevant chip legs, sometimes it’s easier than cutting the stripboard etc.
Again, the photos should be easy to follow, so my description will be brief! Remember Leg 1 is Ground, and so is Leg 7 now that we’ve linked it to Leg 1 on the underside of the motherboard.
That variable capacitor is to tweak the signal, so leave the upper part of the case off, the metal shielding and the heatsink off too. Power the Mega Drive up and, if you can, put something on the 7805 Voltage Regulators (they get hot!), if you can’t, work quickly! Try the console in both 50 and 60 hz modes and see if you need to adjust the screw on the Variable Capacitor to get the colours looking how they should.