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PostPosted: Tue Jan 31, 2017 6:54 pm 
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I've received a SNES to install a supercic mod in, but unfortunately it doesn't boot any games. So I tried a burn-in test cartridge, and initially that didn't give anything but a black screen either. I verified that some voltages are present on all chips and decided to touch up the PPU's and CPU. Tested the burn-in cartridge again and now it definitely booted, but the graphics were all black and white and garbled up, but I could see some resemblance to what it was supposed to display. When I hit start the screen went black and after a few seconds the controller test menu game up, and I could see some graphical activity in the area where it lights up the button that you need to press for the test to advance.
I then reset the console and tried the other menus but they caused the console to hang. After a few minutes I couldn't get the cart to boot anymore either.

I have spare super famicoms for replacement chips. I'm just not sure which one I should try replacing first, given the above. The CPU definitely runs (well.. ran for a bit), but that's about all I can deduce. Dogp's repair logs pretty much indicate CPU the most common culprit, but my symptoms don't match any of the repairs he worked on. Anyone wanna weigh in on what I should replace first?
Also, are all CPU and PPU1/PPU2 drop-in replacements for each other?


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PostPosted: Tue Jan 31, 2017 7:38 pm 
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You didn't say ... did all of the explicit tests in the burn-in cartridge get a pass? (Or can you not tell, because the video is only barely functional?)

It tentatively sounds like one of the two PPUs might be toast. Perhaps PPU1, since sprites sorta work...? Or maybe PPU2, since it's trying to draw things but the palette memory is trashed?

If you have a flashcart, maybe try Magic Floor, spadtest, or my PPU mode demonstration would be obvious things to try.

(edit:)
Quote:
Also, are all CPU and PPU1/PPU2 drop-in replacements for each other?
Rev2 CPU fixes a bug in the DMA controller, as well as changing DRAM refresh timing. Rev2 and Rev3 PPU2 has to change something but we don't know what.

All revisions of the discrete CPU and PPU are form, fit, and function compatible with each other.


Last edited by lidnariq on Tue Jan 31, 2017 9:24 pm, edited 1 time in total.

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PostPosted: Tue Jan 31, 2017 9:14 pm 
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dogp #4 says:

Quote:
Ran test cart, would show garbled main screen, when selected any sub-test, it locked up


Which sounds a lot like what you got when the system booted at all. That was fixed by replacing the CPU, so I'd definitely start there.


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PostPosted: Tue Jan 31, 2017 10:56 pm 
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Most SHVC-CPU-01 2/1/3 units are not fixable. If one chip is damaged, they might all be damaged.

At any rate "black and white and garbled up" suggests your connection first. This is the same kind of effect you would see if you connect the composite or the Y (luma) pin to the Green pin on a 480p component input or only the Y pin on a S-video input. If that's not it, it's the PPU's output doing something similar (eg no red or blue component from PPU2 to S-ENC), the garbled parts are likely between the CPU and the PPU1 or between the PPU's and the video memory.

A screenshot would be helpful, though there is no guarantee that a SNES/SFC can be fixed, the fact that you can boot a game at all suggests that it may be fixable. Systems that just "black screen" when powered always blame the CPU or the CIC chip, but there's no way to tell if all the chips are good.

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PostPosted: Wed Feb 01, 2017 3:01 am 
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I've fixed one sometime ago with a similar problem.
The video was all black and white and distorted.
It was a weird trancodification circuit at the s-enc and a capacitor on the composite video's output.
I remade the transcodification, exchange the capacitor and all went fine.
Hope this helps.


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PostPosted: Wed Feb 01, 2017 4:40 am 
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Thanks for all the helpful replies guys!

lidnariq wrote:
You didn't say ... did all of the explicit tests in the burn-in cartridge get a pass? (Or can you not tell, because the video is only barely functional?)

The tests crashed the console. I managed to start the bottom test #5 (forgot what it was called) which usually shows a bunch of fail/pass messages, but I couldn't tell from the output whether tests passed or not. It definitely crashed during the tests though.

Quote:
If you have a flashcart, maybe try Magic Floor, spadtest, or my PPU mode demonstration would be obvious things to try.

Don't have a flash cart but I frequently use eeproms to play homebrews/translations, so I'll prepare some of these. Will be interesting to see what results are produced.

Quote:
All revisions of the discrete CPU and PPU are form, fit, and function compatible with each other.

Great, good to know. I've seen dogp's test board and figured his socket would cost an arm and a leg, but they're quite affordable it seems!


adam_smasher wrote:
dogp #4 says:
Quote:
Ran test cart, would show garbled main screen, when selected any sub-test, it locked up

Which sounds a lot like what you got when the system booted at all. That was fixed by replacing the CPU, so I'd definitely start there.

Indeed it does. Definitely replacing CPU before PPUs then.

Kismet wrote:
Most SHVC-CPU-01 2/1/3 units are not fixable. If one chip is damaged, they might all be damaged.

Oh well, I got replacements for all chips. Challenge accepted :)

Quote:
A screenshot would be helpful, though there is no guarantee that a SNES/SFC can be fixed, the fact that you can boot a game at all suggests that it may be fixable.

Here's one: http://files.zzattack.org/img/upload/01022017-00142.jpg


Fisher wrote:
I've fixed one sometime ago with a similar problem.
The video was all black and white and distorted.
It was a weird trancodification circuit at the s-enc and a capacitor on the composite video's output.
I remade the transcodification, exchange the capacitor and all went fine.
Hope this helps.

Wow, that does look similar indeed. Additionally the guy who sent it to me told me he also got a black screen but then left the console on for some minutes (as to charge the capacitors) and then it started working. I'll try this first!


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PostPosted: Wed Feb 01, 2017 6:59 pm 
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Recapping didn't help so I'll try replacing the CPU next. I found one that wasn't so nicely desoldered, bent legs and it doesn't sit entirely flat. But with some patience and fine tweezers it'll work, if not I'll have to sacrifice a dirty yellow cheap super famicom.


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PostPosted: Wed Feb 01, 2017 7:12 pm 
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zzattack wrote:
Kismet wrote:
Most SHVC-CPU-01 2/1/3 units are not fixable. If one chip is damaged, they might all be damaged.

Oh well, I got replacements for all chips. Challenge accepted :)

Quote:
A screenshot would be helpful, though there is no guarantee that a SNES/SFC can be fixed, the fact that you can boot a game at all suggests that it may be fixable.

Here's one: http://files.zzattack.org/img/upload/01022017-00142.jpg


Honestly, I'm going to say (based on the color, and the right-hand-side of the screen) that the problem lies in PPU2. It's difficult to really say one way or the other because if the CPU works enough to boot, then the problem is likely not the CPU, but rather the connection between the CPU, PPU's and the video memory. Like at the moment it looks like maybe some of the address lines aren't connected to the video ram so what is ending up in it is garbage.

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PostPosted: Thu Feb 02, 2017 4:17 pm 
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CPU replacement did the trick! Thanks guys.


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PostPosted: Thu Feb 02, 2017 4:33 pm 
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Great! Nice work!
I saw the picture, it was a lot more serious than my problem, unfortunately.


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