SNES test ROM to diagnose PPU failure?

Is there such a thing as a ROM you could put on a flash cart that would diagnose various component failures?

 

The burn in test ROM can sort of help with that, at least sometimes. But honestly, in my experience I usually have better luck just guessing what's wrong. Sometimes even with a bad PPU it'll still pass all the tests on the ROM. Other times it could fail a certain test but you still may not be able to figure out which chip failed to cause it.

Basically, if all games boot and seem to run normally and the only problem is some kind of graphical distortion, one of the PPUs could be bad, although it still could very easily be a bad CPU. I used to repair SNES consoles often and would always use the same test games, so sometimes I would recognize a problem and check to see if I made a note the last time I saw it as to whether it was the CPU, PPU1, or PPU2 that caused it. For example, sometimes when PPU1 fails you'll see vertical bars at the file select screen in Yoshi's Island. So if I ever see that, I assume PPU1 is bad.

If I suspect it's a bad PPU but have no idea which one it is, I'll usually start by replacing PPU1, test, and then if there's no change, I'll replace PPU2. If there's still no change, then it means it's probably the CPU and I just leave the board as-is, since I almost never have any donor CPUs for them.

But you should definitely check out DogP's logs first to see if maybe your problem is listed. It's always nice when you're working on a seemingly difficult problem to find out that someone else has already had it before and documented how they fixed it.

 

I've done a fair number of SNES repairs using a pile of Japanese scrap boards. They were ugly, smelly and yellowed and could be had 25 for about $200. After a while whenever a bad SNES came along where power circuitry wasn't the issue, I just ran the burn-in teset ROM on a donor to confirm donor is ok and if so swapped the CPU. My experience is that just replacing the CPU is faster than debugging everything else first and in over 90% of the consoles I fixed this was all that was needed to get it up and running. Recapping and such is good and all and likely prolongs the console's life somewhat but I've not encountered any that came back to life after a recap job.

 

Yeah, about 90 to 95% of the time it's the CPU that's failed. It's kind of funny though because just today I received these two consoles that both had a similar graphical issue. I was able to fix both just by replacing PPU1. It turned out they both still had good CPUs.

 

My experience has been that the burn in test is much better at detecting CPU failures than PPU failures. So if the test runs and everything passes - but you have corrupt graphics - it's very likely that the CPU is good and the problem is in the PPU.