NES to PC Engine Controller Mod

It’s sometimes not easy to find PC Engine controllers at cheap prices.  It is possible to make your own controller though and it’s not that difficult.  I found an old guide on the web for a US Turbo Grafx 16 mod and once I pulled apart a PC Engine controller it looked surprisingly easy.  It’s common to use a Nintendo Entertainment System Pad because it’s got the same layout and button config, but you could of course adapt this information to convert other pads or make your own joystick!

On the diagram below, the breaks on the board are shown in red.

What you need to know!

First off, here’s the parts needed – 74LS157 chip, 4 330ohm resistors, stripboard (vero board) – 8 tracks tall, and 14 holes wide, 8 pin mini din and some suitably thin cable with 8 wires running through it.

ComponentsBoard with breaks

With the NES pad opened up, we need to remove the existing cable (heat up each of the contact points and pull the wires out one at a time), the remove the chip that’s already on the board.  The chip is a CD4021 (mine actually says MC14021BCP on it), you can either cut each leg and solder onto the legs, or use a desolder pump to remove the solder from each leg and then pull the chip off.

Old chip removed

That’s the NES pad prepared, now that’s build the adapter board.  There isn’t a lot of space height wise in the NES controller case, I chose to mount the adapter board on the back of the existing board.  I got a spare chip and soldered it to an offcut of vero board so I could test fit it, but the legs on the reverse side of the vero board stuck out too far, even after I trimmed them.  So I decided to the solder the 74LS157 chip and resistors on the wrong side of the vero board – this would allow me to cut the legs off.

One side of chip soldered in placeReverse side of board with legs cut off

I found it easier to hold the soldering iron on the copper strip next to the leg, heat the copper up for a couple of seconds before adding some solder and then pressing the soldering iron onto the leg.  Soldering the resistors in is similar, bend them and put them in place, heat the copper up before adding solder and dragging the iron and solder to the resistor leg.  After I cut the legs off, I usually file the rough ends off and get a smooth finish, later on after test fitting it, I usually use double-sided tape to hold it still in the pad.

You can also see that I’ve added some extra solder to the ends of the copper strips, this is to solder the wires onto.

Ready to solder the resistors in placeResistors in place, ready for wires.

Now do some more test fitting and prepare some wires ready to connect both the boards together.  I started by preparing 5 wires for one side of the chip and carefully cutting them to length before soldering them to the relevant spot on the board.  (Yes, I forgot the Ground wire!)  I’ve also labelled some of the leg numbers from the old CD4021 chip to help you count where to solder the wires.

One side of chip with wires.Wires soldered into place.

Now onto the other side of the chip, again I’m using some old ribbon cable from old an old PC IDE cable.

Preparing more wiresFinished linking boards up

Now it’s time to finish it off with the cable and 8 pin mini din.  We have to use 8 core cable so that we get enough wires, but 8 core cable can be quite thick which would make it difficult to fit in the NES pad.  I couldn’t actually find any cable locally but did have a spare cheap 3rd party SNES RGB Scart Cable, I ended up sacrificing this!  Please use the diagram provided above, the table below and the PCE RGB guide to solder up the cable.  Note – Leg 8 of the 74LS157 should be connected to GND on the original board (also leg 8 of where the old chip connected) AND pin 8 of the mini din socket which is the GND signal.

In the photo below I have already carefully test fitted the casing, and made sure none of the wires are going to be squashed by the supports inside the case, I have also stuck the board down with double-sided tape.

Finished cabling

CD4021 Button 74LS157 8 pin mini din
1 6
1 A (I) 2
4 UP 3
4 330 Resistor ->2
15 B 5
7 330 Resistor ->3
8 GROUND 8 8
9 330 Resistor ->4
5 DOWN 10
14 SELECT 11
12 330 Resistor ->5
6 LEFT 13
13 START (RUN) 14
15 7
16 1

Like I said, I found the original guide here, and just adapted it to work with a PC Engine.  I didn’t have a NES pad with Auto-Fire on it, so wasn’t able to test this feature of the original guide out.

The finished pad

Summary of Components

  • 1 x 8 pin mini din plug
  • Length of 8 Core Cable (I used an old SNES RGB Cable)
  • 1 x 74LS157 chip
  • 4 x 330 ohm resistors
  • Strip Board/Vero Board
  • Some wire (I used an old IDE Cable)