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 Post subject: Re: SNES PPU Problem
PostPosted: Sat Jul 29, 2017 9:01 pm 
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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.


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 Post subject: Re: SNES PPU Problem
PostPosted: Sun Jul 30, 2017 1:54 am 
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Probably the one that is closest to the output, which would be PPU2 (5C78).


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 Post subject: Re: SNES PPU Problem
PostPosted: Wed Aug 02, 2017 3:05 pm 
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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.


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 Post subject: Re: SNES PPU Problem
PostPosted: Wed Aug 02, 2017 4:02 pm 
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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...


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 Post subject: Re: SNES PPU Problem
PostPosted: Wed Aug 02, 2017 7:09 pm 
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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.


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 Post subject: Re: SNES PPU Problem
PostPosted: Thu Aug 03, 2017 4:38 am 
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Hopefully an otherwise broken one, because hacking apart a good console would be bad :)


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 Post subject: Re: SNES PPU Problem
PostPosted: Fri Aug 04, 2017 10:19 am 
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That's the idea. It wouldn't make sense to part out a fully functional console.


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