NES:Famicom Disk System Glitching Sprites Fix

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Certain combinations of Famicom and Famicom Disk System (FDS) RAM adapter units have an issue which causes sprites to appear glitchy due to interference on the cartridge slot pins. The issue seems to affect mostly Famicoms with an HVC-CPU-GPM-02 board revision, RAM adapters with boards marked "HVC-FMR-03" and some early "HVC-FMR-02" boards. This issue may also occur when using flash carts and homebrew carts that use 39SFxxx flash chips. Information for this guide was compiled from multiple sources.[1][2][3][4]

Sprite issue affecting Mario.
Credit to Shane from SuperMegaByte.
After sprite issue fix.
Credit to Shane from SuperMegaByte.


Solution

The solution is to add resistors on the data pins of the FDS RAM cart unit, which fixes the interference.

  1. Obtain a 9-pin 4.7kohm resistor array.
    • Alternatively, you can use eight 4.7kohm resistors and solder one end together.
  2. Use electrical tape to line up the resistor array as shown below and hold it in place.
    Credit to Shane from SuperMegaByte.

  3. Bend the first pin of the resistor array upwards so that it doesn't make contact with anything on the board.
  4. Solder a wire between the first pin and ground. Example ground point shown in image above.
  5. Solder pin 2 of the resistor array to pin 6 of the FDS RAM adapter.
  6. Solder the remaining pins of the resistor array to the FDS RAM adapter pins. Pins 6-13 should all be connected to the resistor array.


References

  1. ↑ https://retro.supermegabyte.com/2018/07/23/fix-glitchy-famicom-disk-system-sprites/
  2. ↑ https://www.famicomworld.com/forum/index.php?topic=10607.0
  3. ↑ https://synt4x.org/blog/index.php/2018/01/19/glitchy-graphics-on-famicom-disk-system/
  4. ↑ https://twitter.com/SuperZvesda/status/1639694888944951297
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