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And this is actually a likely thing? The ROM?
I've heard of dirty or damaged contacts, but you really think the ROM might be damaged in a way that it works fine for 99.9% of the time, but then it creates a glitch that looks exactly like a glitch that was actually part of the regular ROM code of PRG0?

I have a Super Mario Bros. 2 cart that's damaged either in the ROM or in the RAM, I'm not sure which, but it has garbage blocks at various places in the level.

And you're sure it's not the contacts? I remember one cartridge that showed garbled graphics and when I temporarily corrected its location in the NES, i.e. established a better connection between cart and NES, the graphics were o.k. until I removed my finger again.

I'd say if you used a frontloader NES it's probably the contacts. I've had issues frequently where graphics became garbled suddently or the game would crash, even though it worked fine for 20 minutes. The frontloader NES connector is just really, really terrible. This do not happen with toploaders or famicom (even using a NES->FC adapter).

It's also likely some bugs were left in PRG1.

I'd say it's extremely unlikely that your ROM chip god damaged.

The thing is that this never happened with any game ever on my NES. Only with "Castlevania", the game that has such a bug hardcoded into its PRG0 version. But on the other hand, there's no single report about this bug appearing in the PRG1 version.

I've never seen this glitch and I played many versions of the game many times. SCN PAL version as a kid (I'd guess it was based on US PRG1 since PAL releases generally come out later than USA), Japanese re-release (the one with easy mode, probably also based on US PRG1) and FDS version (I guess the bug isn't applicable in that one though). I'd say it's unlikely that it's the glitch, but who knows.

Even if all other of your other games are fine it could still be bad pins on that particular cart. Happens all the time for me when I get new carts.

O.k., if the issue happens again, I'll make a photo. Maybe this will show whether it's a glitch or contacts disconnection.

DRW wrote:O.k., if the issue happens again, I'll make a photo. Maybe this will show whether it's a glitch or contacts disconnection.

I'll be impossible to tell: If the miscontacts affects only PRG lines this have no graphical effect. Just one miscontact on one single PRG line for a very short time is enough to crash the game. Unless we could spy the PRG bus somehow, but on real hardware this is very hard to do.

However, it is not unlikely at all some bug remains in PRG1 and was fixed for the PAL and newer JAP release. Just saying.

Bregalad wrote:I'll be impossible to tell

As far as I remember, the sub weapon was dislocated when the game crashed. I.e. it wasn't in the red border anymore, but some pixels to the left. Maybe anomalies like this are enough for an expert to confirm that it's a programming glitch and cannot stem from incorrect contacts.

DRW wrote: As far as I remember, the sub weapon was dislocated when the game crashed. I.e. it wasn't in the red border anymore, but some pixels to the left. Maybe anomalies like this are enough for an expert to confirm that it's a programming glitch and cannot stem from incorrect contacts.

Then it's definitely a bug (assuming other sprites weren't affected). Bad contacts can corrupt graphics, but they cannot move sprites on the screen, as OAM is internal to the PPU and not affected by cartridge contacts in any way. Only if the program does sporadic $2004 writes due to bad PRG contacts could such a thing also happen, but it's much less likely to work without corrupting other sprites.

But wasn't other sprites affected as well?

I suppose it could be the glitch after all. How often does it happen for you?

Bregalad wrote:Bad contacts can corrupt graphics, but they cannot move sprites on the screen, as OAM is internal to the PPU and not affected by cartridge contacts in any way. Only if the program does sporadic $2004 writes due to bad PRG contacts could such a thing also happen

Or if the game does a scroll split for the status bar and fails to keep doing the split after it, and the sprites are no longer aligned with the new incorrect status bar position.

Bregalad wrote:

DRW wrote: As far as I remember, the sub weapon was dislocated when the game crashed. I.e. it wasn't in the red border anymore, but some pixels to the left. Maybe anomalies like this are enough for an expert to confirm that it's a programming glitch and cannot stem from incorrect contacts.

Then it's definitely a bug (assuming other sprites weren't affected). Bad contacts can corrupt graphics, but they cannot move sprites on the screen, as OAM is internal to the PPU and not affected by cartridge contacts in any way. Only if the program does sporadic $2004 writes due to bad PRG contacts could such a thing also happen, but it's much less likely to work without corrupting other sprites.

No, that means the screen was no longer split, and it hadn't updated the horizontal scroll at any time since it last rendered the playfield. Any crash would do that.

No, since he said the subweapon was outside of the red rectangle, and both the subweapon and the red rectangle are sprites. He might have described it badly, though.

How often does it happen for you?

He said this happened once, so definitely not "often".

Oh, I was thinking Castlevania 3, where it's a background and not a sprite. You're absolutely right.