NES dejitter mod

From Retro Modding Wiki
Jump to: navigation, search

The NES and Famicom are known to have somewhat unstable sync. This can cause issues with some TVs, especially when used with the OSSC. Marqs (creator of the OSSC) developed this fix for the issue which removes any visible jitter and increases compatibility with modern displays. The procedure is basically the same for all revisions - replace the stock oscillator with this mod - but the specifics vary. Also note that this mod is only useful if you have already installed the NESRGB, so the guides will assume that this has been done already.

Tools

  • 4.5 mm game bit
  • Phillips screwdriver
  • Soldering iron
  • Solder wick, pump, and/or desoldering iron
  • Flush cutters (recommended)

Materials

  • Dejitter mod
  • Solder
  • Flux (recommended)
  • Wire
  • Double stick mounting tape

General procedure

The idea with this mod is to disconnect the stock oscillator circuit and inject the dejitter mod in its place (though not literally in the case of the NES as it is injected on the NESRGB side of things instead). The oscillator circuit lives between pin 29 of the CPU and pin 18 of the PPU. In the case of the original Famicom, there are capacitors on either side that connect those pins to the circuit. For the toploader, the pins connect through a single capacitor.

  1. Determine how the pins are connected and remove the necessary capacitor(s) to disconnect the oscillator circuit. You should also disconnect the oscillator crystal to eliminate a potential source of interference. Consult the console-specific guide for more information.
  2. If necessary, connect the two pins directly with a jumper wire. Note that they may already be connected, as with the toploader, so check for continuity before adding unnecessary jumpers. Consult the console-specific guide for more information.
  3. On the dejitter PCB, close jumpers JP2 and JP3. I find that a slightly thicker solder works best for this. You may also want to flow a bit of solder onto the other pads at this point.
    JP2 and JP3 closed
  4. Flip the PCB over and trim the leads of the oscillator using the flush cutters so that they will not poke through the tape. I also reflowed the solder so I would get a smooth surface.
    Leads trimmed
  5. Cover the backside of the board with electrical tape.
    Electrical tape added
  6. Add mounting tape to either side.
    Mounting tape applied
  7. On the NESRGB, disconnect the c-sync wire (labeled CS#). This will be connected to the dejitter board later, so leave the other side connected to the output jack. You should also make sure that jumper J8 on the NESRGB is open (not pictured).
    CS# wire removed
  8. Mount the dejitter board to the underside of the NESRGB. You can mount it anywhere that is convenient. This picture shows the board mounted in an NES-101 install.
    Mounting location for dejitter board
  9. Solder the c-sync wire you removed earlier to the CSYNC_o pad on the dejitter board. MCLK_o connects to the CLK pin on the PPU (the third pin in from the right as indicated). I found it easiest to remove some solder from the pin, wrap the wire around it, then resolder it all together. Also solder wires to the 5V, CSYNC_i, and GND pads on the dejitter board. These will be connected to the top side of the NESRGB.
    Connections on the underside
  10. These are the locations to connect the remaining wires from the dejitter board. You can also put the wires in the holes if you prefer. CS# connects to CSYNC_i, GND connects to GND, and +5V connects to 5V.
    Connections on the top side

Famicom procedure

  1. Set up the dejitter board as in the general procedure above.
  2. Remove C4, C9, and XTAL from the motherboard.
    Three components to be removed
  3. Connect a jumper wire between the outside pads of C4 and C9. This picture shows where to connect the jumper (ignore the capacitors since you will have removed them).
    Jumper connections
  4. Follow the general procedure above for connecting the dejitter board to the NESRGB.
  5. Reassemble the console and enjoy!

NES-001 (frontloader) procedure

  1. Set up the dejitter board as in the general procedure above.
  2. Remove C44, C45, and X1 from the NES motherboard.
    Components to remove
  3. Connect a jumper wire between the outside pads of C44 and C45.
    Jumper connections
  4. Follow the general procedure above for connecting the dejitter board to the NESRGB.
  5. Reassemble the console and enjoy!

NES-101 (toploader) and AV Famicom procedure

  1. Set up the dejitter board as in the general procedure above.
  2. If you have not already done so, follow the NES disassembly guide to gain access to the NESRGB and motherboard. You do not need remove the motherboard from the case.
  3. Remove C10 and X1. The top picture shows the components from the top while the bottom picture shows the actual solder points for the components.
    Two components to be removed
    Solder points for components
  4. Follow the general procedure above for connecting the dejitter board to the NESRGB.
  5. Reassemble the console and enjoy!