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 blue blue = all tests passed (the aes does not test the z80 sound ic) red red = work ram error (0x100000 region) green green = palette ram error (0x400000 region) yellow yellow = video ram error (programmed through custom port) magenta magenta = bios self check error (0xc00000 region) cyan cyan = memory card error (only tested if card in unit and blank) no sync / no screen if you have good power for 5v rail, and when you turn on you get nothing at all, not even a sync signal (not even flickering sync that cannot lock on) this could be a dead lspc it could also be the obvious, the av port, av cable, cxa1145 encoder, or traces/capacitors between the av port and the cxa glitched pixels 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 rail this can also be bad wram (cxk58257) near the sound chip and 68k the diagnostics rom will normally tell you if they are faulty it can also be caused by a bad neo c1 or traces to it glitched graphics 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 sprite shapes ok / almost black palette one issue i came across that seems like palette ram, was an almost completely black sprite but with the correct shapes this turned out to be a broken trace from the neo g0 to the 68k on the r!w (read / !write) pin the initial boot screen would be almost all white, with sometimes a black square at the top right, then when games load the sprites are present but almost all black no sprites / backgrounds if you have foreground text like credits and scores, but you have no characters, sprites or backgrounds, then you have either broken traces or bad fv ram (called just vram in diagnostics bios) the fv ram is cxk5814p or cxk5863p that connects to the lspc and there are two chips (upper and lower) flickering small sprite bugs if you have small issues with sprites being glitched and flickering (mainly on scaled objects or in metal slug x on character sprites) on an almost single or few pixels then it is most likely the lspc is bad i fixed one by replacing the lspc2 a2 chip another case was of small few pixel flickers, in random places this was caused by dirt on the lspc pins and reflowing was required to fully fix it in this case the lspc wasn't bad, but the pins/traces to it were sprite doubling & pixel glitches 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, sv video ram or traces between it and the lspc the fv ram is cxk5814p or cxk5863p that connects to the lspc the sv ram is the cxk58257 above the lspc 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 here is ane example where simply old dry flux can cause issues notice the yellow crystal type flux on the pins reflowing this to clean it resolved the issue here is the issue it was causing 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 wrong colors 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