Some variants of the Neo Geo AES such as the 3-6 have a checkerboard pattern over the image.

This is due to the fact the CSYNC pin of the RGB output is sometimes wired directly to the composite video instead of CSYNC.

I am not sure why this is as the CXA video encoder outputs both CSYNC and Composite Video, so there is no reason or need to do this.

If you find your CSYNC pin is outputting composite video (it has continuity to the Composite Video pin on the AV port on CSYNC), then simply cut the trace coming out of the CSYNC pin on the AV port, and solder a 75 ohm resistor from this isolated CSYNC pin, directly to the CXA pin CSYNC OUT.

When routing to the CSYNC OUT pin of the CXA chip, make sure to run the wire away from any RGB data lines and clocks.

After you do this the checkerboard patterns should be all gone.