Introduction: Retro Atari 7800 Mod: Sega Master System Controller to Atari 2600/7800 Hack

About: Jack of all trades, master of none, Sigh...... how does one get good at something when there are so many things in this world to learn?

Today we will modify a super sweet old school Sega Master System controller for full functionality with both the Atari 2600 and 7800.

To be honest, I really wanted to like the Atari 7800 controller. It was shaped like a coffin and looked all space-age and stuff when it came out. But after 10 minutes of using it I knew it was just another SNAFU by Atari. While Europe and the rest of the world got the super cool Atari Joypads with the 7800 release, America had to deal with these horrible POS's.

So, what options do you have? You could try and hunt down an original Joypad on eBay or you can modify one of the other plentiful compatible controllers out there to work for you instead.
Natively the Sega MS controller will work flawlessly with the Atari 2600 but due to the two button design of the Atari 7800, the pinouts are not compatible with this Sega controller. By sacrificing... (and I use that word loosely) an extra 7800 joystick we can merge the two together and build a controller worthy of the Atari ProSystem greatness! Heat up the soldering iron and lets get to it!

Step 1: Whatcha Will Need....

Since we will be merging to controllers together, all you will need is:
1. A Sega Master System controller, both model 3020 and the 3060 "control stick" work just as well.
(I found one at a local used game shop for 3 bucks)
2. A crappy Atari 7800 controller.
(oh crap I have a lot of these bastards...)
3. A soldering iron and solder
4. A de-soldering tool or de-solder braid
5. A Phillips head screwdriver
6. A Pair of wire cutters
7. Bitter frustration and hatred of the damn Atari coffin controllers.
And as always...
8. Plenty of good cold beer...
......for this project we will be consuming some New Belgium: Fat Tire.

Step 2: Crack It Open...

So first we crack open a cold one and then both of the controllers.

The Atari 7800 joystick is held together with just 2 screws on the back side and the Sega Master System controller has 6 little annoy screws to contend with.
Once the Atari controller is apart, disconnect all the colored leads by sliding the connectors off of the main circuit board and also the two joystick fire buttons. I do have to applaud Atari for designing and making modular parts that were easily replaceable once worn out. The 2600 controllers were the same way, just slide off the connectors and then back on to a new board and you were ready to go!
At this point I clip off all the connectors located on the end of the wire harness and leave the ones that are located by the strain relief part of the cable (namely the lower Yellow, Red, and Orange connectors). See picture below.
Also using a sharp knife or razor, remove the stain relief from the cable ... carefully as to not cut through the wires!!!
Next, de-solder the two (2) 620 Ohm resistors on the Atari 7800 circuit board along with the diode ( the only other component on the board) and place them aside for later.

Then on to the Sega MS controller... desolder all the connecting leads including the connecting ground wire (the bare wire running between both boards).

Once finished, we are now ready to merge them together.

Step 3:

With some small modifications, the Atari controller cable will now be soldered to the Sega MS circuit boards.

Connect the wires to the D-Pad board in the following order.
The circuit boards are labeled with the corresponding numbers.
1 = White wire (controls the "Up" movement)
2 = Blue wire (controls the "Down" movement)
3 = Green wire (controls the "Left" movement)
4 = Brown wire (controls the "Right" movement)
8 = (will get connected to the diode in just a sec)

The other board is the "button" board. We will have to modify this one slightly for the hack to function correctly. In order for the 7800 controller to be backwards compatible with the Atari 2600, the Atari engineers designed the separate fire buttons to behave as one when playing 2600 games.

To make this happen, take a sharp X-acto knife or similar tool and cut through the trace as displayed in the picture. Test the cut with a continuity meter to make sure there is no connection at all between the black ground wire and the button pad terminals.
Also with the same knife, carefully scrape through the solder mask to expose the fresh copper circuit board. Now solder the Orange wire to the circuit board to the exposed place on the trace you just created as like in the picture.

The connection for the trigger board is as follows:
8 = Black wire (this is the common Ground)
The Atari's Left and Right fire buttons get connected as follows:
6. Yellow Wire (Left Trigger)
9. Red Wire (Right Trigger)
This will make the Sega button 1 the Left Atari button and button 2 the Right Atari button.

As in the picture ... connect one end of each of the two resistors that we removed from the Atari circuit board, the other ends will get soldered to the Yellow and Red connectors that we didn't clip off. Once finished put it aside until we connect the diode to the boards.

The Diode we removed from the Atari controller will replace the jumper wire that connected the grounds on both SegaMS controller boards.
!!!!! You must attach the diode facing the correct way or else the controller will not work. Diodes only allow current to flow in one direction!!!!!
On closer inspection of the diode you will see that one side is flat and the other has an indention on it, this is the side (indented side) you will have facing the fire button board... NOT the D-pad side. Now we will connect to the flat side of the diode the two resistors we connected together. This should finished off the soldering!

Carefully stuff the contents back into the controller being cautious not to allow any shorts from bare contacts touching each other. (It would be helpful to wrap the Yellow and Red resistor connections separately with electrical tape to keep them from touching each other when putting the controller back together.)

Once the back lid is on and screwed together, plug it in and get on to some serious 7800 gaming!!

Thanks for reading and if you enjoyed the tutorial and found it useful please rate it!

Step 4: Final Thoughts...

I feel this controller is such a marked improvement from the uncomfortable and behemoth 7800 controllers. The fire buttons are so much more responsive and the D-pad doesn't leave your hand all cramped up after 10 minutes of playing... ah such joy!

The SEGA control stick is very similar in construction. I have posted a few extra photos on how to wire it up if you choose to do this unit instead. Should be easy to figure it out based on the pics.

Next I plan to mod a Sega Genesis controller for the Atari... it uses some different circuitry so there is a bit more to mod but the good news is that the cable has wires running for all 9 pins so you don't need to sacrifice a 7800 controller's wires. My only Genesis controller has a short in the cable so when I can get a newer one I'll post the mod also.

Thanks for reading and I hope this helps!!