Neo Geo:General Troubleshooting

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This page serves as a starting point for troubleshooting general errors with your Neo Geo MVS. If all else fails, you can check the operation of commonly failing individual chips and see if any require replacements.

Testing Video

Turn on the Neo Geo with all game(s) removed. After a few seconds, it should boot to a blue grid. If you are able to see the grid, your video output is okay.

Testing Hardware

Flip DIP 1 to ON to enable test mode. See the Neo Geo:Test Mode page for more details.

Common Symptoms

Garbled Graphics

Garbled graphics or sound issues can be caused by:

  • The cartridge being inserted upside down. Ensure that the arrow on the cartridge is oriented closest to arrow on the motherboard/shell.
  • Dirty pins on the cartridge or connector. See the Cartridge Cleaning page.
  • The cart being too tight and not inserted all the way. This might happen if the cartridge and/or Neo Geo shell was painted, adding extra thickness.
  • The motherboard being flexed by inserting a cartridge too hard, resulting in cracked traces near the cartridge interface.
  • Needing to reflow the NEO-GRZ or NEO-273 chip.

Vertical Stripes on Sprites

Freezing on Green Screen or CALENDAR ERROR Screen

Freezing on the green screen generally indicates a calendar error.

  • Look for a leaking battery on the motherboard corroding nearby traces.
  • Check the clock crystal next to the D4990 chip and try reflowing the pins and the capacitors near it.
  • Turn all DIP switches on and allow the work RAM test to run for 15 minutes, then power off the unit, turn all DIP switches off, then power it on and see if it bypasses the calendar error.
  • Installing Unibios will bypass this error altogether.
  • If all else fails, it may be an issue with the NEO-BUF chip. There are cheap replacement chips for this, as described on this page.

System Not Booting

A faulty NEO-E0 chip prevents the system or specific slots (on multi-slot systems) from booting. A replacement can be purchased here.

Sound Issues with Single Game

Your game cartridge may have a faulty PCM chip. A replacement can be purchased here.

Memory Card (or VMC) is "Write Protected"

If you receive various memory card related errors and a message saying "memory card write protected" when trying to format the card, there are a couple things to check.

  • If you are using an AES, check continuity between the BIOS chip pin 22 and the NEO-E0 chip pin 1. You may need to solder a wire connecting the two if the trace is broken.[1]
  • If you are using an MVS:
    • If you have a physical memory card, check continuity between pin 15 of the memory card (write enable) to pin 6 of the HC32 chip. You may need to solder a wire connecting the two if the trace is broken.[2]
    • If you are using a Virtual Memory Card (VMC), ensure that you removed the original BIOS chip and that none of the pads are bridged. Simply disabling the chip is not enough.