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Megadrive Version 1 (Mk. 1) with modifications - visible changes: widened cartridge slot, region select pushbutton, bi-colour power LED.

This is a simple console modification utilising a PIC16F627A. Because I used a microcontroller this mod is better and neater than the usual slide switch mod. A baseline 12F PIC with serial EEPROM would have worked but I did not have any in stock.

Once modded the Megadrive is able to play European, Japanese and American cartridges with the use of an RGB SCART cable. The UHF and composite outputs do not work with the 60hz territories (Japan and USA) because the Megadrive outputs an invalid PAL signal when running at 60hz. Therefore an RGB SCART cable is needed so you can use the raw RGB signal which is correct in both 50hz and 60hz modes.

Let me clarify - when used in the original european mode the UHF and composite outputs continue to function properly. For all other regions an RGB SCART cable is required. I have a modification here to correct that.

You can obtain a nice RGB SCART cable via eBay. I obtained one with a stereo lead to plug into the headphone port at the front for stereo sound - as the DIN socket on the back only outputs a mono sound signal.

This modification is completely safe to do to the console, it will not damage the Megadrive in any way if fitted properly. You can switch regions during game - this allows you to boot a game with a region lockout and change to a different region later on. Note this crashes some games and makes others break/run too slowly/run too quickly, but some games support multiple regions and run better at 60hz because the PAL ports were not proper ports. As the switching is digital this will not ever harm the console.

The region setting is remembered during power off by storing it in serial EEPROM, so you don't need to cycle through all the regions again if you turn your Megadrive off for a break and switch it back on later with the same game.

Many Megadrive games were very badly ported from the originals designed for 60hz consoles to our 50hz PAL consoles. The majority of ported games run at only 83.4166% of the speed of the originals, and a few have slower music (Sonic 1 is an infamous example). This modification allows you to import Japanese or American games and play them on your PAL Megadrive, at the original speed of 60hz. Region locked games will boot as long as you select the correct region at startup.

Some PAL releases are multi-region games that auto detect the type of console and run on all consoles. Sonic & Knuckles is an example and with this mod you can play your PAL copy at the proper speed - 60hz - without any glitches. This works as Sega cut costs by using the same hardware in a few games regardless of region. Unfortunately most games are not like this, for example even if you bypass the region check in Sonic 3 it will run very badly when you change to Japan or USA - the music is too fast and the game runs very slowly with glitches. For those games you will need to import a non PAL copy.

A few games will display Japanese text if you boot them with your Megadrive set to the Japan region - or display English text in European or USA modes. Some even display alternate title screens! I have personally seen this happen with Columns (Japanese text), Revenge of Shinobi (becomes Super Shinobi) and Streets of Rage (becomes Bare Knuckle with Japanese text).

I fitted a non-latching push button to the rear of the console and replaced the power LED with a bi-colour LED. Each push of the button cycles to the next region without resetting the console. The current region is indicated by the colour of the power LED.

• Europe - red LED, 50hz English
• Japan - green LED, 60hz Japanese
• USA - orange LED, 60hz English

I am going to modify the code to add the ability to start in the default European mode by holding down the button while switching the Megadrive on - and a special mode to bypass region lockouts conveniently if you wish to run European games in 60hz modes without lots of button pushing.

Red is used for Europe because the stock LED in an unmodified Megadrive is red. Therefore when playing games originally designed for the PAL console it looks unmodified from the front. You can (and should) alter this behaviour if you apply this mod to an NTSC console.

I got the original wiring diagram (motherboard jumper pin outs) from mmmonkey's Megadrive mod page.

To cut the costs of producing different versions of the Megadrive for each region it was sold in Sega designed the motherboard to support both 50hz PAL and 60hz NTSC.

At production time the region of a Megadrive is set by fitting a different master clock crystal (depending on PAL or NTSC) and setting some jumper links on the board.

This mod works by altering the jumper settings. There are 2 jumpers on the board that are important. One selects 50/60hz (display refresh), and the other selects English/Japanese language. At the factory these jumpers are hard wired to +5v or ground depending on the region of the console. These 2 jumpers on the board are cut to remove the factory setting and the mod circuit then controls them.

Keen eyed readers will note that I don't correct for the master oscillator differing between PAL and NTSC boards. This does not affect game play but does mean that a bad RF/composite signal is generated when the modded Megadrive is not set to the original factory region. All mods like this are affected by this shortcoming. However you can apply my PAL 60 fix to resolve that issue as mentioned earlier on this page.

• 1x microcontroller - PIC16F627A
• 1x Bi-colour 3mm LED, red/green, 2 lead
• 1x 10uF electrolytic capacitor
• 1x 100nF polyester or ceramic capacitor
• 3x 1K resistors
• 1x 220R resistor
• 1x 18-pin IC socket
• 1x normally-open non-latching push button
• 1x 6-way square pin header 0.1“ pitch
• 4x lengths of wire, all the same length and different colours - about 20CM
• 2x lengths of wire, both the same length, same colour - about 30CM
• 1x piece of strip board
• Some wire to use for jumpers, and possibly 0R resistors for convenience

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• MPASM source code
• Firmware image for PIC16F627A

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First you need to get into your Megadrive. Remove the 6 philips screws from the bottom of the unit. One at each corner and 2 in the middle of the long sides.

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Carefully lift the case away - 2 wires are connected to the power LED. Bend the 2 LED legs until they stick straight up and slide the plug away from the LED - this will take some force.

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You should be left with this. Push the 2 white plastic lugs in either side of the LED to loosen the power LED retainer. Turn your Megadrive case the other way up.

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Remove the power LED retainer and set it aside (don't throw it!). You can now pull the LED out. Discard it (or re-use it for another project!).

Now you need to widen the cartridge slot or Japanese games will not fit. Remove the 3 screws holding the shutter assembly and set the screws and assembly to one side. Widen the slot until the edges are almost straight. I used an old blunted pair of side cutters to cut the plastic, and smoothed it down nicely with a needle file. Test fit with a Japanese game. Replace the shutter assembly. Set the Megadrive lid aside.

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We need to remove the RF shielding to get to the motherboard. Remove the philips screws circled and set them aside.

Remove the circled screws. Lift off the RF shield carefully. You may discard it if you wish but purists may want to put it back. It isn't needed and it is far easier to route the wires and perform other mods (what other mods? come back later to find out!) without it. It also gives you more room to mount the mod circuit board.

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Ever wondered what makes your Megadrive tick? :) I suggest at this point that you clean up any dust/hair you find inside the Megadrive. Use a needle to carefully remove hair from the cartridge slot and clean the slot using contact cleaner while you are at it. Make sure you do a good job of it - it'll be quite dirty and once you are done all of your games will work first time, every time.

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We are going to prepare the Megadrive for modding. First cut off the power LED connector as close as you can to the motherboard. That green plug is not actually a plug - it is soldered to the board. Cut the wires flush with it and keep the power LED connector for later!

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You need to cut a hole in the case for the push button. I recommend cutting the hole in the back next to the other connectors. There is a convenient blank space there as original Japanese Megadrive units had some kind of serial port there. If you use an electric drill please be careful as it is easy to slip and damage the board. I used a small hand drill and a reamer to enlarge the hole until the push button fitted nicely. Do not fit the push button yet.

You need to cut 2 traces on the motherboard. These 2 traces set the console to 50Hz English (Europe region). You need to cut the traces between the left and right pads on JP2 and JP3.

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A close up of the traces I cut. Make sure the cut is good - use a multimeter to confirm this. Failure to do this properly will prevent the mod from working and could damage your Megadrive. Set aside your Megadrive for later.

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Gather the parts for the mod. The parts list and schematic is above on this page, before the images. Please note I accidentally picked up the wrong resistors - 10K ones instead of 1K - in the following pictures and I had to change them out right at the end when I tested the board! Don't make that mistake or it wont work properly!. Just saying this in case keen eyed readers notice this in the pictures. I have some 0 ohm resistors for convenience but you can use normal pieces of wire for all links.

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Cut your strip board to a convenient size and start fitting the components. I find it easier to fit all of the components apart from the PIC first before I fit the jumper wires. Please do use an IC socket and do not solder the PIC directly. General good practice.

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Getting there. See why I said you needed to save the power LED connector? Solder the power LED connector to the board (leave the wires as long as possible). You can also see the PICkit 2 programming connector. It is a very good idea to mark pin 1 on the PICkit 2 connector by colouring the board around it black with a marker!

See the microchip data sheet for the PIC for a connection diagram, I may be updating this page at a later date with a wiring diagram for your convenience.

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Very near completion. All wires have been soldered to the board, and the push button has been soldered (to the brown wires).

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At this stage it is a good idea to test the board. Make sure NONE of the wires are going to short to each other or the board. If you have a bench power supply you can apply +5V across the red and black wires, then probe using a multimeter to make sure everything is okay. Failing that connect PICkit 2 and tell it to apply VDD at 5V to the board and make your tests. Then remove power, put the PIC into the socket (make sure you put it in the right way round!) and plug PICkit 2 back in. It should detect the PIC16F627A :) If not, check all connections and make sure nothing is shorted.

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The fun bit. Plug the power LED into the power connector. Connect a logic probe to the red and black power wires, connect PICkit 2 and tell it to apply power to the board. Flash the firmware into the PIC and once it finishes, push the button once. The LED should light red. If it lights green, you have inserted it backwards.

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Now use the logic probe to check the 50/60 and Jap/Eng wires. Check both of them, then toggle the region and check them again. Repeat for all 3 regions to make sure they are switching as they should be.

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If it all went well, here is your mod board ready to fit into your Megadrive :) You may want to use some hot glue to secure the wires to prevent them accidentally breaking away from the board. But please make sure your board works before you do that.

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Tin the 4 pads on the motherboard you will be soldering to. JP2 left, JP3 left, JP1 right, JP4 right. Using the wiring diagram near the top of this page, solder the 4 wires to the correct places. From top to bottom the order is:

• JP1 right - Ground
• JP2 left - English/Japanese language
• JP3 left - 50/60 screen refresh rate
• JP4 right - +5V

If you used coloured wires like I suggested this will be a piece of cake :) Soldering the power wires backwards will probably blow up the microcontroller and cause the electrolytic capacitor to pop! You have been warned. Make sure nothing is shorted - double check your work before you continue.

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Fit the board into the top half of the Megadrive case. I do this by putting some hot glue on the case then pushing the board onto it. Then I add extra hot glue at the corners. Be careful not to get hot glue on the PICkit 2 connector. Fit the push button to the back of the Megadrive case and route the wire carefully. Use electrical tape to hold things down.

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Time to fit the new power LED. Drop the legs down through the case and clip the retainer back in. If you are not sure of the polarity, push the power LED connector on slightly and power the Megadrive up. Confirm the regions cycle in the order - red green orange. If not, reverse the connection. Now push the connector on all the way (the legs will stick out of the back) and really make sure it is on all of the way (push the LED from the front with a pencil) before you continue. Bend the legs over completely (180 degrees) and cut them short.

You are now the proud owner of an all region Megadrive. Carefully route the wires so as to avoid the case edges and Sega CD connector. Put the case back together - careful now as the headphone slider and power switch need to be aligned perfectly. Screw it down. You may want to add some labels for a nice professional touch.

I have worked out how to modify the Megadrive to output a valid PAL signal when in 60hz modes. See this page for details.

I have encountered problems with a modded Megadrive set to 60hz connected to a very cheap LCD TV with an RGB cable.

The TV was getting confused by the fact that it could see a bad composite signal. It kept switching between RGB mode and composite mode continuously causing a jumping picture. As the TV was very cheap it had no way to stop it from switching between the 2. Note that better (big brand) LCD TVs do not exhibit this problem.

Also note that this would happen still even if you applied a simpler slide switch mod.

The fix is to apply my PAL 60 mod. This is a tricky mod to do as you have to tune the oscillator but it is definitely worth it. Once done, the megadrive should work perfectly on cheap LCD TVs.