I've just about admitted defeat on a Galaxian board I'm working on. It has a sprite issue where in the attract mode, the aliens appear on the wrong row (see first photo). In the game the attackers sometimes appear in the right place, sometimes on the wrong row. It's all repeatable showing the same fault every time, and not intermittent.
I wrote some code to display the sprites on screen, starting at the top then working their way downwards - initially 1 on the screen, then 2, 3...up to all 8. It works fine when 1-7 are on there, once 8 is drawn all 8 sprites show constantly at the bottom of the screen (I've tried to show this in the photos the best I can - one shows 3 sprites falling from top to bottom, then 6 sprites. The picture with all 8 is trying to show that they don't move top to bottom but are all pinned to the bottom of the screen regardless of the position they're meant to be at).
Does anyone have any idea what could be causing this, and why it only happens when sprite 8 is brought onto the screen? Attack, object and video RAM are ok, as are graphic ROMs, 74163 counters and all the simple logic feeding the attack RAM. Everything else on screen displays correctly, just the sprites are wrong.
I wrote some code to display the sprites on screen, starting at the top then working their way downwards - initially 1 on the screen, then 2, 3...up to all 8. It works fine when 1-7 are on there, once 8 is drawn all 8 sprites show constantly at the bottom of the screen (I've tried to show this in the photos the best I can - one shows 3 sprites falling from top to bottom, then 6 sprites. The picture with all 8 is trying to show that they don't move top to bottom but are all pinned to the bottom of the screen regardless of the position they're meant to be at).
Does anyone have any idea what could be causing this, and why it only happens when sprite 8 is brought onto the screen? Attack, object and video RAM are ok, as are graphic ROMs, 74163 counters and all the simple logic feeding the attack RAM. Everything else on screen displays correctly, just the sprites are wrong.
