Sega Nomad controller mod

Started by trisoret, March 28, 2012, 10:11:37 AM

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Hello, I just ordered a new LCD screen to install on my old Sega Nomad & I was looking all over, for years, to find a mod that allows me connect a Genesis controller to port 2 and play as player 1.

Is that even possible? If someone has already done it, can you please explain how?

Thank you.


That's a good question.  I don't have a nomad handy, but for anyone who wants to pursue this, the first thing I'd do is figure out where the inputs from the P1 controller go.  I had a look at some internal shots I made years ago, and couldn't really tell.  Chances are the inputs from P1 and P2 go to a dedicated chip that handles them.

If you're lucky, there'll be a 74157 chip inside that converts the single-line-per-button to the Genesis' encoded signal, and you can simply swap that output for the P2 connector's signals...  But I doubt you'll be lucky.  You may have to snip the P2 inputs and decode them, and feed them into the P1 circuit yourself.

Sound like fun yet?  =)


Thank you so much Lawrence, I will tweak around the board a bit & try to figure things out, any available pictures or videos that might offer a little help here?


What I'm also trying to do is:

I can play the Nomad using its controller BUT whenever I hook up a Genesis controller into Port 2, the main controller will automatically stop working and I'll be controlling player 1 through port 2.
(Just like the SupaBoy (A portable SNES that I recently got))

I'm sorry for not explaining that earlier in my first post.


Did you ever figure this mod out?


The chip that I believe controls P1 inputs is the chip: Sega 315-5638-01, I believe the same chip that controls 6 button controllers (not sure because I don't have one).

You can see it in this photo:

I found this website in Spanish, looks like the pinouts are known:

and translated:

It looks like to me that this chip encdoes the inputs, then it is sent to the ribbon cable. Lawrence, if this acts similar to a 74157 can I just connect to the "ribbon" side of the chip and assume the signals will be sent to control? It seems that simple? I hope I don't have to remove this chip because that would just be a mess, and the pins are tiny. If so I plan to do this a little different, I will just install another controller port, so two people can play (and hook up to TV via the Svideo port that I installed).


found this, I am thinking I just need to create a port for P1 and wire it to pins 16-22, and also give the controller port "5" on the connector 5V. Think that would work? In my mind it seams like it would make sense.


Ok well the theory worked, built the circuit and here is the video:

Sega Nomad Controller Mod


That's quite remarkable, and a little bit surprising, actually.  I didn't really expect Sega to just shove the standard encoder chip in there.  Nice bit of work, duo_r.  =)



ok got it all wired up, nice stock looking port (I built it similar to the P2 port):

One small problem, once I got everything put away, holes cut for the DB9, my final test the Genesis Controller Up / Down doesn't work. I am a little baffled right now because Left / Right works, so does Start and all the buttons. I retraced everything, all is connected properlly, but no luck. 6 Button controllers aren't detected at all.

Based on what I know, it seams like the Select line is not detecting the Up / Down signals. I am a little baffled since it is all done but no dice. I can't help to think that pin 7 is the issue somehow. Maybe the controllers got fried? Need to test on another Genesis. Any theories because this baby is almost done.

BTW - the stock controls work just fine, it is just the new controller port that is the problem.

Another weird things - Street Fighter II seems to detect 3 Button as a 6 Button controller since hitting Start pauses the game (and holding left causes character to walk left and jab (when character is in "kick mode).

Here is my theory - I have to disable the built in 315-5638 chip, and I htink I have to do that but cutting 5 V. Anyone think that sounds right? I think the system is polling two controllers and getting confused. What is weird is why this worked perfectly when I did the Youtube video....


update - controllers are fine just tested on a Genesis. Any ideas on what could be the issue? I might have to lift pin 24 or cut the trace and then add a switch.


2nd update - ok lifting pin 24 (VCC) on th 315-5638 chip did the trick! It disabled onboard controls, and the DB9 functioned properly. Now here is the only weird thing - how did the game even work in the first place???

Here is my theory - in my video I played Sonic, I never ducked down I don't think, so it would seem as if it was working properly.

Then on Street Fighter II I used a 6 button controller, but a 3rd party controller. Perhaps this one didn't not "trip out" the onboard controlls like the official one did when I did my final test. That's the only thing I can think. I know many times 3rd party controllers use different chipsets so maybe it seemed to work fine in conjunction with with the Nomad.

So here is the plan, I already have a 3 pin switch hooked up to turn the screen on / off. I will just wiring up 5V to the onboard chip when the screen is powered on (shares the 5V line) and when it is switched off power will route to the DB9. Now I understand why another member disabled onboard controls when they did this mod (Because you have to).

This is how I will tackle it unless someone has another idea on how the DB9 port could be "detected" and somehow onboard controls disabled. I am thinking that somehow it will be like a switchless mod for a Saturn.


Unfortunately the Saturn-type mod won't work (it was my first idea too) because the Saturn checks the status once on boot and never again, where that chip will come alive every time the initial condition is not met.

But, if you use a latching circuit of some sort, you can detect once (watch for any of the pad inputs to be pulled low when the pad is connected, probably) so that your new circuit does the check-once thing instead.

Alternatively, a physical switch, like a long-lever microswitch, that is closed when the pad connector is inserted into the socket.  A small notch in the connector shell, and a bent piece of wire (a paperclip for example) would work very well, and if you can secure the switch itself, probably be simpler to install.


Ok turns out after lifting the pin for 5V, all the issues went away. Onboard and external controllers work fine, not exactly sure why the onboard isnt affected but it works great, so no switch needed.

Ok some finished pics of the additional mods.

Here you can see the P1 controller port, and also the physical reset button. Also the brightness wheel was replaced with an on/off switch for the LCD, for improved battery time when hooked up to a TV. The reset button is resessed enough that it won't be accidentally pushed. You have to give it a good press with your finger.

And here you can see the S-video port and also the LCD buttons to control the brightness and screen settings:


F*ck yea

General Chaos anyone?


and 9 years later....

The 1UP MOD for the Sega Nomad.
Use the Sega Nomad Player 2 port as Player 1.
Install and invasiveness moderate.
The Nomad and external controllers work but not at the same time.
Reversible but not switchable.
Lift a pin, run seven wires and remove two EM components.

Removing vcc from pin 24 will lead to the early death of the 315-5638 chip.
The instructable will be removed because of this problem.

1UP MOD for the Sega Nomad.
Use the Sega Nomad Player 2 port as Player 1.
Install and invasiveness moderate.
Reversible but not switchable.

Lift a pin, run seven wires and remove two EM components.

How to:
1. Find the 315-5638 chip and then carefully cut the trace in front of Pin24. (Or cut and lift Pin24)
2. Run the 7 jumper wires on the main board as shown. Pins 1,2,3,4,6,7 and 9
3. Remove the 2 EM's that connect Pin6 (EM6) and Pin9 (EM8) or remove 7 of them. Do Not Remove EM5.
---Alternately cut the 2 traces that connect pins 6 and 9 shown in the picture. Not recommended.

Removing pin24 VCC partially disables P2 I/O on the 315-5638.
This allows input from the external Player2 port to the internal inputs of Player1.
The jumper wires complete the input circuit from the Player2 port to Player1 of the 315-5638.
Removing EM's further and completely disables Player2 input on the following pins.
Player 2
Pin6 - A/B Buttons – EM6 – Required – Remove EM6 (or cut trace not recommended.)
Pin9 - Start and C buttons – EM8 – Required – Remove EM8 (or cut trace not recommended.)
Pin1 - Up/Z - EM1
Pin2 - Down/Y – EM7
Pin3 - Left/X – EM3
Pin4 - Right/Mode – EM4
Pin5 - 5V – Do Not remove this - EM5
Pin7 - Start – EM2
Pin8 - Gnd

The EM components are not listed in order on the Main Board.
So this can be confusing.

Information and inspiration

Excellent Nomad capacitor replacement work and more by retro-_-mancer 

Credits: erexx, micronut99 and duo_r, Outer Heaven.

1. Soldering iron with fine tip.
2. Solder and flux
3. Wire. 26 AWG or smaller.
4. De-soldering gun highly recommended,
5. Scalpel or small sharp razor blade.
6. Jewelers Loop or some other magnification.
7. De-soldering gun or flush cutters.

How to:
1. Find the 315-5638 chip and then carefully cut the trace in front of Pin24. (Or cut and lift Pin24)

2. Run the 7 jumper wires on the main board as shown. Pins 1,2,3,4,6,7 and 9
Click on image to fix aspect ratio or see the instructable website.



3. Remove the EM's  1, 6 and 8 or remove 7 of them. Do Not Remove EM5.

Example 2 - back of the board.

EM1 has not been removed yet in this example.