Graphical issues

[Pat the Cat]

it could be one of several things;-

1) Bad memory chip, U18-U19. (Upper MB, because games loading OK, computer starts up OK). Likely cause static damage

2) Bad connection beteen the memory chips and the custom chips (tiny break or short, maybe from the recap).

3) Bad custom chip, Alice but most likely Lisa. The memory and pathways are fine, but the chip isn't reading it properly.

If you do a memory check of the machine, I guess that could rule out option 1 at least, if it passes. It will only test the paths between the processor and the memory chips though, could still be OK custom chips but maybe a board fault somewhere between the memory chips and the custom chips.

It definitely looks like it's digital, rather than  when it gets turned into an analog signal.

https://aminet.net/package/util/moni/CheckMem

https://github.com/keirf/Amiga-Stuff#amiga-stuff-native--cross-dev-code--tools-for-amigas

Duff memory chip would be easier to find replacement. Than a duff Alice or Lisa.

[Pat the Cat]

<Waggles Fingers> I wouldn't depend on that. For one thing, which version of Diagrom? Different versions test differently.

One thing to try if the games are for older Amigas (not AGA) - hold down both mouse buttons while starting and choose ECS or OCS rather than AGA.

Then try running the game again. If it cures it, no fault, it's just AGA trying to understand old games "hitting the metal",.

If these are AGA games, different story. They're not working for some hardware fault reason,

And no, points 2-3 not covered by testing the memory with a memory tester and finding all the chip RAM is fine. There are still the connections between chip RAM and the custom chips to consider.

EDIT: I'm pretty sure will be messed up on composite output too. But the games were both released before AGA was and that might be the reason they don't display properly.

[Pat the Cat]

Regarding booting into ECS or OCS, I see no direct option for these, but I guess you are referring to "original" under the "display" option in the boot menu? When booting using original, the game Pang for example just goes to a completely red screen when the level starts where as enhanced or best boots in normally to the game but with the game glitches as described before.

I guess I'd just expect different (more random) bad results if there is a physical connection that is broken, but I really have no idea, its far from my expertise.

Well these are both old games. It does look like a memory issue but it's only happening on a couple, both involving dual playfields.

Maybe the code is written in such a way that the background playfields work correctly when run on a 68000 with 512K of chip RAM, but don't calculate the right offsets with a 68020 and 2MB of chip ram. That might explain it.

WHDLoad versions of Pang and James Pond are  available, the notes mention Blitterwaits being used on non-68000 machines (and obviously not in original code).

http://www.whdload.de/games/JamesPond.html

http://www.whdload.de/games/Pang.html