SNES Mode-7 Failing

[extrarice]

Has my SNES finally given up the ghost after 24 years? It appears that any mode-7 layers are now garbled, but the other layers display fine. I first noticed it when starting up Actraiser, and the spinning/stretching logo was not holding together. I re-seated the game and connectors, and tried again, yielding the same results. I then popped in Mario Kart, and the course layer was distorted as well, but the sprites are fine. The Iggy fight in the first castle of Mario World also exhibits the problem on the tilting shell.
I opened the case to visually check the capacitors and they look fine. Any ideas, or is it one of the chips on the mainboard?

actraiser.jpg (50.4 KiB) Viewed 1787 times

mario.jpg (61.1 KiB) Viewed 1787 times

[Flake]

This happened to mine a few years back. Pour one out for the homies.

[Ziggy587]

Could be the PPU, yeah.

My oldest and most hour logged SNES developed a similar problem. It will display garbled graphics, but not exclusive to mode 7 like yours. There's just ALWAYS garbled graphics on the screen, and the garble moves when sprites move (for example).

I've seen this type of problem brought up on a few forums, but never seen any one post a definitive cause, just speculation.

[Xeogred]

Sadly just going to have to agree with the others above here, my first SNES that browned and was pretty beaten up started doing this. I tried the same carts out on another SNES console when I had one available and they were all fine there. So I guess it was just time to retire the brown one.

[extrarice]

Thanks, all. I was hoping there would be a quick fix to resurrect the thing. In doing a bit of search engine research, it seems that this sort of problem is starting to be come more and more common as the hardware ages. Since the chips are mostly custom-built, and replacements are not readily available, the only real option is to cannibalize functional parts from one system to repair another. Eventually there will be no more equipment to cannibalize from...

How well do the third-party "Retro" systems work for SNES?

[Ziggy587]

How well do the third-party "Retro" systems work for SNES?

I'd rather make a emulation box and and use bSNES / Higan. Add a Retrode if you need to use your carts.

Eventually there will be no more equipment to cannibalize from...

What's interesting is that the SNES had two PPU chips. I wonder if PPU1 goes bad on some SNESes, and PPU2 goes bad on others. That would allow you to transplant one and make a working console.

I had also wondered if the problem could be caused by bad RAM. I have no idea if the video RAM is on board the PPU, or if it's a separate RAM chip. I know that there is at least one (stand alone) RAM chip on the SNES main board. It should be possible to replace this RAM chip with something off-the-shelf, if it is indeed the problem.

edit: On my SNES that I mentioned had a similar problem, I was actually planning on testing if it was the RAM chip that I can see on board. The only way I really have to test it though is swapping it out with a known working one. As it were, I have a SNES mini that is broken in some other way, and I know the RAM chip is fine. A visually comparison shows that it's the same package as my earlier (fat) SNES. I just haven't gotten around to actually swapping it, mostly due to the fact that I'm not even sure if that RAM has anything to do with video.

[arcadifvid]

ohh i had a rather similar issue (SMW,actraiser plays still fine, contra3 on the other hand..) to yours i asked months ago. but yeah looks like SNESs are failing. had to get another unit which works. but ive really lessened my usage of the old consoles already

[extrarice]

How well do the third-party "Retro" systems work for SNES?

I'd rather make a emulation box and and use bSNES / Higan. Add a Retrode if you need to use your carts.

I have plans to set up a MacMini to an HDTV and run OpenEMU, but dangit, original hardware is part of the fun.

Eventually there will be no more equipment to cannibalize from...

What's interesting is that the SNES had two PPU chips. I wonder if PPU1 goes bad on some SNESes, and PPU2 goes bad on others. That would allow you to transplant one and make a working console.

I had also wondered if the problem could be caused by bad RAM. I have no idea if the video RAM is on board the PPU, or if it's a separate RAM chip. I know that there is at least one (stand alone) RAM chip on the SNES main board. It should be possible to replace this RAM chip with something off-the-shelf, if it is indeed the problem.

I know very little about electronics, but if it were bad RAM, I would expect to see more randomly-appearing problems. Like, whatever is stored at that corrupted RAM address would be glitched, and the glitching would change from one graphic to another as the system swaps out what is stored in the RAM at that address. Since this seems to be limited to only a very specific sprite transformation, and it's consistently applied there, I think it's more likely that whatever part of the PPUs handle the mode-7 math is returning corrupted values, which get fed to the video-out. Which I imagine could be bad traces on the mainboard, some kind of arc between two traces that shouldn't be, the voltage may be off, or a physical problem in the PPU chips.

[Exhuminator]

If it was me extrarice, I'd pop open that SNES and look for this chip:

I'd check all the pins for corrosion or detritus. If there's gunk like that going on, I'd clean the pins carefully and isolate them as they are supposed to be. A lot of times with chips like this, it's short circuits caused by crud doing wonky things, but not the chip itself actually being fubar.

[extrarice]

I'd check all the pins for corrosion or detritus. If there's gunk like that going on, I'd clean the pins carefully and isolate them as they are supposed to be. A lot of times with chips like this, it's short circuits caused by crud doing wonky things, but not the chip itself actually being fubar.

I popped open the box over the weekend and completely removed the mainboard, checking both sides for signs of corrosion or wear. All the traces on the board looked clean, and there were no leaking or swelling capacitors. Nothing on the pins of any of the chips that could potentially create a short. It pretty much looks factory-new. Near the DSP and sound processor there is something that appears to be adhesive that I believe was present from the factory, as it is hard/cured.
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