I'm working on fixing up a 1943 PCB. I've resolved most of the issues it had (controls not working, messed up scrolling background graphics) but there's still a problem remaining with the sprites that I just can't seem to solve and it's driving me nuts. As you can see from the photos, the sprites (planes) look fine until they go over top of any of the scrolling background objects (clouds). When the planes go on top of the clouds, it looks as if only every other line of them gets drawn. I've been over almost the entire bottom board with a logic probe, following the schematics from the graphics ROMs to where the data goes back out to the main board, but I can't find anything obvious.
Can anyone offer some suggestions for where to look? It seems to be a problem with whatever circuit is responsible for integrating / blitting the sprites on top of the background tiles, but I'm not sure where in the schematics that would be. Any help would be greatly appreciated!
Can anyone offer some suggestions for where to look? It seems to be a problem with whatever circuit is responsible for integrating / blitting the sprites on top of the background tiles, but I'm not sure where in the schematics that would be. Any help would be greatly appreciated!

