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 Post subject: Help fix an SNES
PostPosted: Mon Jan 15, 2018 5:46 pm 
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Hello, I'm having video artifacts on some games, here is a little bit of the history:

Sometime ago (before I've learned that they're bad) I bought one of those cheap Aliexpress knockoffs.
BIG mistake! :oops:
I played it a lot, them after I found it could kill my console I retired it.
I played other games, but this one was the only one with a 3v IC (MSP55LV160A) and no level shifter only a diode on the +5v.
Recently I saw a flashing background on Super Turrican and some artifacts on the Donkey Kong 2's 1st stage.
After I ran the SNES Burn-in test, I discovered it fails the DIV 16/8 test.
AFAIK, this failure is related to the S-CPU.

Now, the questions:
Would this cheap knockoff be THE responsible for this failure?
Could this problem be caused by some broken track or other component? Or is it internal to the CPU?
Is there a good place I can buy these parts? I could get some old SNES boards, but I'm not sure if the CPU of any of them is fine.
Can this failing function be rebuilt with a circuit made of discrete logic ICs? I really think not, but I'm asking anyway... Maybe with an FPGA...

Thanks in advance.


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 15, 2018 6:31 pm 
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>Would this cheap knockoff be responsible for this failure?
Probably not. The higher voltage part damages the lower voltage part. Unless the wiring is very bizarre or the memory addressing isn't quite correct. I still can't see any way to cause damage in an otherwise working game other than by causing overheating.

>Could this problem be caused by some broken track or other component? Or is it internal to the CPU?
The divider hardware is internal to the CPU chip, implemented as custom digital logic sausage next to the core.

>Is there a good place I can buy these parts? I could get some old SNES boards, but I'm not sure if the CPU of any of them is fine.
It's a shot in the dark anywhere when buying used. But your odds of having another CPU with the same issue is tiny.

>Can this failing function be rebuilt with a circuit made of discrete logic ICs? I really think not, but I'm asking anyway... Maybe with an FPGA...
The circuit can be duplicated, but pointless because they'll fight each other. You cannot disable just the failing divider unless you decap it and zap it with a laser in a vacuum chamber. You could duplicate the whole CPU in an FPGA, but that requires an insane amount of logic level shifting to 5 Volts.


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 15, 2018 6:35 pm 
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whicker wrote:
The higher voltage part damages the lower voltage part. [...] I still can't see any way to cause damage in an otherwise working game other than by causing overheating.
Er. Overheating of the high voltage part's output drivers is how low voltage parts damage high voltage parts.


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 22, 2018 12:13 am 
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The bad cart could have been part of it. However SNES consoles are known to have failures perhaps more so than other consoles of the era. My original SNES developed some sort of internal failure in one of the two PPU chips causing a line of garbage in sprite cells. The only "fix" was to swap the PCB from my original case with a PCB from a donor system with yellowed case but 100% electronics.

The cheap bootleg cart is probably best filed in the trash bin. Be wary of buying such things in the future. You'll never know if it was the cause, a contributing factor, or not a factor at all. But as lidnariq pointed out it's not a good idea to directly interface parts that operate at different voltages. It's not good for either of them if they were not designed for it.


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 22, 2018 3:05 am 
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MottZilla wrote:
Be wary of buying such things in the future.

Yes, I agree it was a big mistake, and probably I'll never be sure of the cause of the console's malfuncion.
At least now we have a possible positive example of the damage these things can do.
But the worst thing is that some sellers here in Brazil are selling these cheap knockoffs as "quality made reproductions".
If I remember correctly there's even tutorials on Youtube showing how to do repros with 3v parts and even pointing to sellers who sells these chips and adapters. :shock:
MottZilla wrote:
The cheap bootleg cart is probably best filed in the trash bin.

Maybe I could try to use its board and change the ROM to a 5v tolerant one.
I just can't imagine how big would be the mess if I try to add a shift converter to it.
Would be better do design a new board.

Other thing that bugs me is that according to these logs, the CPU problem is the most common SNES failure cause.
I have 2 dead SNES' boards and am afraid to try to switch the CPUs because it may be the cause of their deaths too.
Damm!! All this could be avoided if I could only get originals.
Unfortunatelly scalpers around here had made this almost impossible to me. :cry:


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 22, 2018 11:46 am 
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Do you mean original games? Or original what?

If you want to play games that you cannot obtain then buy a Flash Cartridge like the SD2SNES, PowerPAK, or EverDrive. I believe all have proper designs that won't harm your system.

If those are too expensive to obtain then making your own socketed EPROM cart and using 5V EPROMs is another option. Or even making single "reproductions". Atleast that way you'll know they aren't going to cause damage. If you get any "repro" from a 3rd party you should examine it or have someone that knows what to look for to try to spot any issues before using it.

You could try to replace the ROM with a 5v part on that board you got. I agree as you said it would become a mess to all level shifting into it but it could be done.


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 Post subject: Re: Help fix an SNES
PostPosted: Mon Jan 22, 2018 2:43 pm 
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MottZilla wrote:
Do you mean original games?

Yes, I meant original cartridges.
Sorry if I wasn't clear enough. :oops:
MottZilla wrote:
buy a Flash Cartridge

Yes, a flashcard would be the best solution ever. :beer:
MottZilla wrote:
I believe all have proper designs that won't harm your system.

I'm using this page as reference.
I think it was cited by another NesDev user a while ago.
The guy has good arguments and I think he's right.
According to him, the only 100% secure flashcard is the SD2SNES, wich costs more than my notebook did.
Emulators may be a good solution, but it's not the same thing.
MottZilla wrote:
Or even making single "reproductions".

I've done some repros with old/damaged PCBs, but unfortunatelly I have easy access only to 2Mbit (256KB) flash ROMs, at least for now.
It's possible to make SNES games, but since most of them are 8Mb the end result gets a bit "ugly".
Here is a little example of the mess. This is a 4Mb game I made from a damaged PCB:
Attachment:
20170618_182754.jpg
20170618_182754.jpg [ 676.74 KiB | Viewed 382 times ]

Attachment:
20170618_182744.jpg
20170618_182744.jpg [ 659.06 KiB | Viewed 382 times ]

I think I should learn how to make simple PCBs and do an adapter to put 4 PLCC chips + a demux on a board. :)
Would a veroboard make things better?
MottZilla wrote:
If you get any "repro" from a 3rd party you should examine it...

Most sellers from Mercadolivre (a kind of EBay here) post pictures of the game's board when asked.
Unfortunatelly some just won't care and don't post anything, or worse, curse and block me!
Sometimes I think it's me who isn't communicating properly with these guys... even in my mother language, wich is a shame!! :(


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 Post subject: Re: Help fix an SNES
PostPosted: Tue Jan 23, 2018 9:44 am 
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Don't worry, the guys not replying and instead just blocking you are most probably scums trying to make money.
OR they're guys with the know-how but just too busy to communicate properly about things simple to them, because they're also just trying to make money.
Have my random 50ยข, please :)


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 Post subject: Re: Help fix an SNES
PostPosted: Wed Jan 24, 2018 5:21 pm 
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Fisher wrote:
MottZilla wrote:
Do you mean original games?

Yes, I meant original cartridges.
Sorry if I wasn't clear enough. :oops:
MottZilla wrote:
buy a Flash Cartridge

Yes, a flashcard would be the best solution ever. :beer:
MottZilla wrote:
I believe all have proper designs that won't harm your system.

I'm using this page as reference.
I think it was cited by another NesDev user a while ago.
The guy has good arguments and I think he's right.
According to him, the only 100% secure flashcard is the SD2SNES, wich costs more than my notebook did.
Emulators may be a good solution, but it's not the same thing.


I don't believe he mentioned the PowerPAK for SNES at all. I don't think Bunnyboy overlooked voltage levels of parts. I had seen an article on the subject that mentions the NES PowerPAK checks out so I would imagine the SNES does too.

I forgot that the SNES EverDrive may have a poor voltage translation scheme. You also might try to see if you could find a 90s era Copier in your area. The Game Doctor SF series is excellent. So are the Wild Card copiers. There are others too.


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 Post subject: Re: Help fix an SNES
PostPosted: Thu Jan 25, 2018 3:24 am 
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MottZilla wrote:
The Game Doctor SF series is excellent.

Yes, I've heard they're pretty nice hardware too.
I planned to get one around the year 2000.
But again they cost an arm and a leg around here. :cry:

I even got an adapter that alowed to use a SmartMedia card on a floppy drive, like this one, but I just can't find it now.
I never was sure if this would work at all but since it was very cheap I tought it was worth a try.
It also had no manuals or software...


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