Today I have finally once again a working SNES. This has been a bit of a project that started last week.
It started when I saw some cheap DC-DC switching regulators on Aliexpress. I have been curious about these for a while and the price was right. So I bought a couple of 7805s just to test:
I have some Sinclair ZX computers that I would like to run a little cooler but for my experiment I chose my SNES that has a badly broken case.
First I just took a photo of the screen with the normal 7805:
And then I changed it to the DC-DC variant. Well it worked but now I had these horizontal lines on the screen which honestly was anticipated:
So now I tried to add some filter capacitors of different capacitances and somewhere around here it all went wrong. I don't know if it was ESD, a charged capacitor that I shorted to something or just that the SNES didn't like the treatment but suddenly the SNES was dead. I did all the checks I could but the console was completely dead. I let it sit for 10 minutes and felt all the chips and the only one that was hot was a clock chip. It was of course a Nintendo branded chip so I had to look around for a spares console online and so I got one "untested" the same evening for 6 euros. As you can imagine it was dead on arrival but now I could change the chip, so I did and no change. Well I did some more experiments with the new board and found that it would actually boot with a multicart. Great, but no games were working, some started to load and froze but most just gave me a black screen. What threw me off was that Rareware games seemed to work perfectly, it played Donkey Kong country 3 without problems and some other Rare-games worked to some extent. I still cant understand why they worked as well as they did. There are diagnostic carts for the SNES but I couldn't get them to load through the multicart (later I found out that you have to change some settings in the menu to get it to work).
Somewhat perplexed I started researching a bit more and found that the old SNES-consoles have primarily CPUs that go bad, but the other proprietary
chips too. I have never in the PC world seen that CPUs can be partially working. Either they work or they don't, but it seems that the SNES CPU, which is an improved version of the 65c02, can execute some code despite being broken. The failures seem to happen at an alarming rate which is somewhat worrying. There are also some SMD-caps that leak on these consoles and destroy traces, one of them because Nintendo actually used a polarized cap instead of non-polarized one.
Anyway, for a last hail Mary I changed the CPUs between the boards and wouldn't you know it, the new board starts working!
I'm an amateur at best at soldering so I was really surprised and happy that it worked. I used hot air for desoldering and then drag soldered them. First I tried solder paste but that was just a mess.