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SNES PPU Problem
http://forums.nesdev.com/viewtopic.php?f=12&t=16270
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Author:  MottZilla [ Sat Jul 29, 2017 9:01 pm ]
Post subject:  Re: SNES PPU Problem

AWJ wrote:
A bad connection between the PPU and VRAM would affect BGs as well as sprites, and I don't see how a bad connection between PPU1 and PPU2 could affect just one out of every 8 pixels like that (the pixel bus between the two chips carries one pixel at a time) I would guess that one of the on-chip data lines to the line buffer on PPU1 has failed--not something that can be fixed short of replacing the chip with one from another SNES.


So one of the PPU chips probably had an internal failure? I do agree that the connection to VRAM is probably fine. I thought maybe it could be something communication related between PPU1 <> PPU2 but if it's as you say then I guess some internal chip function has failed. Are you fairly sure it's PPU1 that would have the failure? Or could it be PPU2? I guess I'll have to find someone to swap it out but being sure which of the two is defective would help.

Author:  creaothceann [ Sun Jul 30, 2017 1:54 am ]
Post subject:  Re: SNES PPU Problem

Probably the one that is closest to the output, which would be PPU2 (5C78).

Author:  MottZilla [ Wed Aug 02, 2017 3:05 pm ]
Post subject:  Re: SNES PPU Problem

Does anyone else have an opinion on which PPU is at fault? It'd be easier and cheaper to only have to replace 1 PPU chip and not both.

Author:  lidnariq [ Wed Aug 02, 2017 4:02 pm ]
Post subject:  Re: SNES PPU Problem

It's going to be hard to find these as loose parts. (By which I mean, someone else is going to have to have opened a SFC/SNES and pulled the IC using good equipment in order to send it to you)

And it's a big enough surface-mount device that you'll really need a hot air rework station to remove the one on your mainboard anyway...

Author:  MottZilla [ Wed Aug 02, 2017 7:09 pm ]
Post subject:  Re: SNES PPU Problem

I don't plan on doing any of that myself. I don't have those tools or skills to do that. But should I decide to get it done it would help to be pretty confident in which chip is bad. For the time being I did the more sensible thing and just acquired another unit.

Author:  creaothceann [ Thu Aug 03, 2017 4:38 am ]
Post subject:  Re: SNES PPU Problem

Hopefully an otherwise broken one, because hacking apart a good console would be bad :)

Author:  MottZilla [ Fri Aug 04, 2017 10:19 am ]
Post subject:  Re: SNES PPU Problem

That's the idea. It wouldn't make sense to part out a fully functional console.

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