Snes CPU 01 graphics issue

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sidgallup
Posts: 14
Joined: Thu Mar 28, 2019 8:09 am

Snes CPU 01 graphics issue

Post by sidgallup »

Found this first revision CPU-01 unit at a flea market, after cleaning it and replacing all caps, now it runs every game on first try but theres some minor issues with them.
Attached are some pics, in Mario World and Yoshis Island theres a vertical line that is more noticeable when the coins rotate, this line rotates in synch with the coins kinda like a "shadow" that should not be present at all, also when the picture is scrolling theres also lines that appear in the background, its like objects in background have a "shadow".

Also in Street Fighter these same lines appear only in the character portraits in the intro, they do not appear at all ingame, the sprites look fine, so whatever this issue is, it only applies to background objects (PPU2 maybe?). Another thing that ive noticed and has only happened 3 times in all the hours ive been testing this unit, sometimes theres wrong sounds playing, for exsample one time in the SF2 intro when the logo and menu screen appear, i could hear the punch and kick sound fx, another time in the Mario World intro movie, i could hear the music that should start whenever you touch the star power up, and another time also on Mario World in the intro movie i heard the sound fx when the time is running out and then the music speeds up.

Really weird issue and now im not sure if its only related to graphics since it also has shown signs of bad logic in the game. Any hint appreciated, i have a few donor boards that i could salvage chips from but i need some guidance asa to where should i start.
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20230103_202820.jpg
20230103_202233.jpg
20230103_201847.jpg
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jeffythedragonslayer
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Joined: Thu Dec 09, 2021 12:29 pm

Re: Snes CPU 01 graphics issue

Post by jeffythedragonslayer »

Do you have a cartridge dumper like the Retrode? You could load ROMs into an emulator and that could help you distinguish whether this is a cart or console issue.
Fiskbit
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Re: Snes CPU 01 graphics issue

Post by Fiskbit »

I would not expect it to be a cartridge issue because there are clearly multiple games suffering from similar issues, suggesting multiple cartridges unless a flash cart is being used.

Since you're having issues beyond just graphics, maybe there's a problem getting data off the cart, either with the data pins or perhaps the peripheral "B" address bus. I suggest ensuring the cartridge slot is clean. There are others here who can suggest more technical causes, as well.
creaothceann
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Re: Snes CPU 01 graphics issue

Post by creaothceann »

If you have a SD2SNES / FxPak Pro / Super EverDrive / cartridge with (E)EPROMs you could load test ROMs, e.g. Nintendo's test cartridges.
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10
sidgallup
Posts: 14
Joined: Thu Mar 28, 2019 8:09 am

Re: Snes CPU 01 graphics issue

Post by sidgallup »

I dont own a Flashcart so im unable to run the Burnin Test at the moment, these are all different genuine cartdridges, all display similar issues, so far i have meticulously cleaned the cart connector from the top and bottom (this revision has a removable pin connector) , applied fresh solder to the cart connector pins on the PCB. checked with a magnyfing glass for any suspicious dark spots on any trace on the side of the video chips but it looks really clean, and still no change.

My first step should be going for it and start replacing chips on the video side one by one, i think i should start simple and replace the video RAM chips first, one by one and testing each time, but after that it gets more difficult since PPUs have more pins and smaller, so, IF i come to the point of having to replace the PPU chips, which one is in charge of drawing the background objects? i think ive read somewhere that PPU1 is in charge of the sprites, and since the issue here is not with the sprites but with the backgrounds and objects then i assume PPU2 should be the first to go.

Is this correct? or where would any of you start?

EDIT: Well i just replaced both video RAM chips and the issue is still exactly the same, so that rules out faulty VRAM, now, before i move on to replacen PPU2 i have a silly question... as i was recapping this unit, one of the ground pads on one cap lifted and broke, attached is a diagram of this board and marked in red is the cap with a broken ground pad, what i did to fix the broken ground pad was just solder the ground legs on those 2 caps together, ive done that before in other devices and to my knowledge this would not affect anything, but maybe Snes consoles are sensitive to this kind of stuff and thats whats creating this "noise" in the video output... can someone confirm that soldering theese 2 caps together would be fine? i just need to be sure im not going crazy here.

Anyways, i would have some free time this weekend and will shoot for a PPU replacement... still not decided which one should i do first.
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SNES-SHVC-CPU-01-Cap-Map.png
sidgallup
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Joined: Thu Mar 28, 2019 8:09 am

Re: Snes CPU 01 graphics issue

Post by sidgallup »

Final update, issue was solved by replacing PPU2, ive been testing the unit for the last 4 days and everything seems fine. Just as a piece of tivia... are the PPU1 and PPU2 chips the same? i mean, can i put a PPU2 chip on the PPU1 socket and viceversa or are they different?
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Individualised
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Re: Snes CPU 01 graphics issue

Post by Individualised »

They're different - one is a Ricoh 5C77 and the other is a 5C78, they serve different functions so they're not compatible.
lidnariq
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Re: Snes CPU 01 graphics issue

Post by lidnariq »

One of the two is responsible for backgrounds, the other for sprites. One is responsible for controlling what VRAM address is fetched at each moment, the other for combining all the data and running it through the palette and video DACs.
sidgallup
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Re: Snes CPU 01 graphics issue

Post by sidgallup »

Ahh great to know, so judging from the issue this console had, i guess PPU1 is in charge of sprites and PPU2 does the backgrounds. Thanks for your replies, 1 console fixed 1 to go so i should make another topic since this one has a completely different issue.
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mikejmoffitt
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Re: Snes CPU 01 graphics issue

Post by mikejmoffitt »

I just encountered basically the same issue today on an SFC I got from a junk shop. I had similar glitches every 8 pixels or so, and I mistakenly thought it might be PPU1. After replacing PPU1, I replaced PPU2, and this issue went away.
sidgallup
Posts: 14
Joined: Thu Mar 28, 2019 8:09 am

Re: Snes CPU 01 graphics issue

Post by sidgallup »

Nice to see another Snes console rise from the dead, what ive learned from this issue is, first test as many games as you can and try to find out if the corrupted graphics happen only to background objects (PPU2) the sprites (PPU1) or maybe both, thats a good start at troubleshooting and chosing where to start replacing chips.
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