Visual Diagnostics (Neo Geo AES)
The default BIOS of the Neo Geo AES has some built in basic diagnostics.
Turn on the console, without a game, and if you see a solid colour screen then it indicates the possible cause.
- īģŋBlue = All tests passed (The AES does not test the Z80 sound IC).
- īģŋRed = Work RAM error (0x100000 region).
- īģŋGreen = Palette RAM error (0x400000 region).
- īģŋYellow = Video RAM error (programmed through custom port).
- īģŋMagenta = BIOS self-check error (0xC00000 region).
- īģŋCyan = Memory card error (only tested if card in unit and blank).
If you get glitched pixels without any sign of actual game data (no moving graphics or logos where you would expect) without a game, with a game, with diagnostics ROM (they all act the same) this is slight under voltage on the 5V rail or excessive noise on the power rai
If you can clearly see the console loading as you might expect, but in place of where graphics would be, you get garbled pixels or repeating pixels, it is often the CXK5814P video RAM attached to the LSPC, or traces to and from them.
It could also be the other CXK58257AM video RAM also attached to the LSPC.
If you get glitches that are not whole chunks of sprites, and instead much smaller glitches, usually noise, lines and so on, but often the overlay graphics like Credits are perfectly fine, this is usually the FV RAM or traces between it and the LSPC.
The FV RAM is CXK5814P or CXK5863P that connects to the LSPC.
If you get sprite doubling, which is also sometimes followed by small pixel glitch lines too, it is usually the SV RAM or traces between it and the LSPC. It can still be the FV RAM as well.
The SV RAM is CXK58257AP or UPD43256 that connects to the LSPC.
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If the Palette RAM is swapped and known good, check with oscilloscope all the address and data pins are ok and high voltage pulses, as continuity is not always a good test as you cannot see if the signals are valid.
It can be the NEO-B1 (GPU) itself bad. I have seen this on pin 3 (PA3) is bad on the GPU itself.
If you have wrong colors, and sometimes slight visual block glitches, it is almost always the Palette RAM, or traces between it and the NEO-B1 or Flip Flops.
The Palette RAM is CXK5864BP or UPD4364.
If the Palette RAM is swapped and known good, check with oscilloscope all the address and data pins are ok and high voltage pulses, as continuity is not always a good test as you cannot see if the signals are valid.
It can be the NEO-B1 (GPU) itself bad. I have seen this on pin 3 (PA3) is bad on the GPU itself.
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