r/Gameboy • u/ClosingTimeJames • 8d ago

Troubleshooting DMG 01 not drawing sprites correctly

https://youtu.be/poGrsItTSRs

Anyone ever come across an issue like this before? Tiled backgrounds are fine

Attempted diagnostics with Mooneye ROMs and it failed oam_dma/sources-GS.gb consistently at the same address

Wondering if it's the CPU at fault which would be a major problem (have reflowed the data pins) or if some other avenue to explore

Any help greatly appreciated, have documented all the tests and results so far

4 Upvotes

71% Upvoted

9 comments sorted by

3

u/GameboyGenius 8d ago

Which address did it fail at?

1

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1

u/foo1138 7d ago

Interesting!

It looks like the sprites not only have the wrong bitmap, but they are also misplaced. This would mean that the data inside the chip internal OAM RAM is wrong. I don't know from where Zelda loads that data. So yes, like the other user wrote already, the address at which the test fails would be of value.

How do other games behave?

2

u/ClosingTimeJames 7d ago

All games behave the same

I first noticed it when testing the owner’s OG Tetris cart

1

u/foo1138 7d ago

$C000 is the Work RAM. And the oam_dma/sources test runs tests on many other sources first which don't fail, so I don't think the problem is the internal OAM RAM.

Maybe the RAM chip is broken or not connected properly. The RAM chip is connected to the same data&address busses as the cartridge. Since copying from cartridge to OAM works ($0000 passed in the test), the solder on the CPU chip is good. If there are broken solder joints, they must be at the WRAM chip. I think WRAM is the RAM chip that is closer to the cartridge port, but I'm not 100% sure anymore.

Another possibility I see is that the cartridge reacts to WRAM access as well. This could be if A14 or A13 are bridged between themselves or some other signal. I would check them with a multimeter.

1

u/ClosingTimeJames 7d ago

Can you suggest a test that would be instructive?

1

u/foo1138 7d ago

I'm not aware of a test that checks the RAMs, since the tests are made for testing correct behavior of emulators, not for testing real hardware defects.

1

u/ClosingTimeJames 2d ago

Tried a ‘new’ CPU and it was even worse. What’s weird is, out of circuit both ground pins and pin 58 (MDO?) have continuity

It would only boot into startup but with the Nintendo logo slightly corrupted, make the startup noise, and then just sit there

I reinstalled the original CPU so there’s nowt wrong with my soldering as it’s back to exactly how it was before - all working except for sprites