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PostPosted: Sun Mar 24, 2019 5:19 pm 
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I've got a skyfox cartridge which has had the sram removed and replaced. However, when I try to play the game, it plays the music, but there is no graphics. I do sometimes get some graphical glitches that looks like it's trying to load, but then it stops.

I'm wondering where the traces go from the right side of the U2 sram chip on this picture, since they seem to go off the side of the board. I've traced every other one that I can see where it goes and they all seem fine. But the right side confuses me. Any ideas?


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PostPosted: Sun Mar 24, 2019 6:57 pm 
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I once had a similar problem with this game.
It was a bad inductor.
I ended up putting a external clock generator, so I could use an unmodded GameGenie on it and get a slightly overclock. :-)

Edit: Hey! I think I know this hand in the picture!! :-D


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PostPosted: Mon Mar 25, 2019 5:24 am 
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I think you do lol. I did steal it! Muahahaha.

Seriously though, I ruined it myself, due to not knowing there were different versions of the FX chip. Tried to make a SF2 lol.

I've got a new inductor on and it still does the same, so I'm pretty sure it's the sram. I tried putting it up to 512, but then discovered it wouldn't work, so I put it back to the original 256.


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PostPosted: Mon Mar 25, 2019 7:44 am 
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Nice!!
I feel happy this pic had helped someone else! :-)

Maybe if you can carefully switch an old SNES PPU RAM chip.
I think it has 2x 256Kbit.


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PostPosted: Mon Mar 25, 2019 5:26 pm 
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Well let me show you my terrible terrible board lol.

As you can see, it's not very pretty, but from what I can tell, they're all making proper connections even if it is burned. And the chip looks ok. I tried putting the 512 back on instead and it did the same thing, so I'm thinking it's either the sram connections that I can't trace, something obvious that I can't see or I've probably ruined the board.


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PostPosted: Wed Mar 27, 2019 6:50 am 
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Well, the soldering work doesn't seems too bad to me, I've seem very worse!
At least you didn't put generous amounts of hot glue!! :-)

I tried to find some program that could test the FX chip and its RAM without success. :-(
Maybe some of the gurus around here know or can make something tha can test it?
Of course, this will only be usefull if yo can somewhat easily change the ROM of the PCB.


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PostPosted: Wed Mar 27, 2019 8:13 am 
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Easiest way for testing would be cartiridge dumping (if you have any such hardware). For the sram it should preferably also support writing to sram, instead of just dumping rom or sram.

Or if you have a flashcard or the like (and know how to write snes software), then you could brew up some test tool on your own, something that displays the rom checksum, and that tests writing and reading sram content. If you can do that: The most reliable way to get through hotswapping is to execute some small code in dma "memory area" at 43xxh while swapping cartridges.

A bit offtopic: I wasn't aware that there are PAL aka SNSP boards for MC1 chips. And I don't see a direct requirement for that in this case (since the CIC is mounted externally, and I don't think that there is framerate selector pin on the MC1 chip). Some differences are the SMD L1 instead of the uninstalled 74HCT04 chip, and the dual D1 diode (for whatever purpose), and maybe most importantly: two ground contacts for shielding (if that should be a requirement in europe).
Hmmm, and looking at where the D1 diodes are connected to the MC1 chip... that looks as if MC1 pinout is yet a bit different than GSU-1 pinout : /

PS. for the ROM chip (or EPROM or whatever you have connected there), you know that nintendo ROMs have slightly different pinouts than, say, EPROMs?


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PostPosted: Wed Mar 27, 2019 9:10 am 
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nocash wrote:
Easiest way for testing would be cartiridge dumping (if you have any such hardware). For the sram it should preferably also support writing to sram, instead of just dumping rom or sram.

Or if you have a flashcard or the like (and know how to write snes software), then you could brew up some test tool on your own, something that displays the rom checksum, and that tests writing and reading sram content. If you can do that: The most reliable way to get through hotswapping is to execute some small code in dma "memory area" at 43xxh while swapping cartridges.

A bit offtopic: I wasn't aware that there are PAL aka SNSP boards for MC1 chips. And I don't see a direct requirement for that in this case (since the CIC is mounted externally, and I don't think that there is framerate selector pin on the MC1 chip). Some differences are the SMD L1 instead of the uninstalled 74HCT04 chip, and the dual D1 diode (for whatever purpose), and maybe most importantly: two ground contacts for shielding (if that should be a requirement in europe).
Hmmm, and looking at where the D1 diodes are connected to the MC1 chip... that looks as if MC1 pinout is yet a bit different than GSU-1 pinout : /

PS. for the ROM chip (or EPROM or whatever you have connected there), you know that nintendo ROMs have slightly different pinouts than, say, EPROMs?

I don't have any hardware for dumping the cartridge, only my TL866A for programming the eeprom that I replaced. No flashcard either, though I wouldn't really have any idea how to write something like that.

Yeah, it is a little different. As you can see, I replaced the inductor on L1 with a 27uH one, like what was mentioned in Fisher's other thread, I figured, it worked for him, so I'll just go for the same number, but no luck.

As for the double ground contacts, I'm not sure why it has that as the cartridge only has one connection, even though there is a space for another.

As for the eeprom I connected, I do know that the pinouts are a little different. It's only an 8mb game, so I used a 27c801, which only needs two pins changing. I did have the game working at one point before I switched the sram back to the original 256, which is why I thought that was the issue. I just can't see anything wrong with any of the pins I can trace, which is why I was wondering about the ones the go off the side. They don't seem to go to ground, so I'm not sure what's up with that, as with pin 26, it doesn't seem to have a trace going anywhere, which is why I think they do go somewhere, I just can't figure out where.

Edit: Sometimes I get strange graphical things happening on the screen. This is one, would this be an sram problem do you think? Or perhaps the rom not loading correctly?


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PostPosted: Wed Mar 27, 2019 10:12 am 
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SRAM pin26 should be A13 and that should connect to the MC1 chip. For the repaired SRAM wires, are you sure that they're wired to the correct pins? The short wire on the photo looks as if were connected to the wrong pin - but then, the photo is only showing the isolation of the wire, not where the actual wire is connected to.

In general, I would have kept the ROM and SRAM installed on the board (and only rewired the chip select signals, instead of physically removing the chips). That might have helped to avoid damages during desoldering, or when pulling at the cables.

Don't worry about the dummy wires that go to the board edge, I am sure that they are solely used for production/testing... although I don't really know what for exactly. Does anybody know more on that?

I know that the cart edge connector would require such dummy wires for applying the gold contacts during manufacturing, but the wires on the other board edges seem to have a different purpose. Or more commonly, Nintendo PCBs have such dummy wires ending in a hole with a few millimeters in diameter (instead of ending at the board edge).


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PostPosted: Wed Mar 27, 2019 11:10 am 
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nocash wrote:
SRAM pin26 should be A13 and that should connect to the MC1 chip. For the repaired SRAM wires, are you sure that they're wired to the correct pins? The short wire on the photo looks as if were connected to the wrong pin - but then, the photo is only showing the isolation of the wire, not where the actual wire is connected to.

In general, I would have kept the ROM and SRAM installed on the board (and only rewired the chip select signals, instead of physically removing the chips). That might have helped to avoid damages during desoldering, or when pulling at the cables.

Don't worry about the dummy wires that go to the board edge, I am sure that they are solely used for production/testing... although I don't really know what for exactly. Does anybody know more on that?

I know that the cart edge connector would require such dummy wires for applying the gold contacts during manufacturing, but the wires on the other board edges seem to have a different purpose. Or more commonly, Nintendo PCBs have such dummy wires ending in a hole with a few millimeters in diameter (instead of ending at the board edge).

Ah, I didn't realise they went via the back of the board. I've checked them though and there's constant continuity between the pin and the mc1 chip, so it doesn't look like there's a problem there.

For the repaired wires, they did have continuity too, but it seemed a little intermittent, so I put the wires in just to make sure. So I'm pretty sure they're connected correctly and there's no bridging anywhere that I can see.

To be honest, I'm not quite sure what you mean by rewiring the chip select signals, I'm somewhat new to this, as can be assumed from trying to turn it into SF2 lol. I found a post on another site about upgrading the sram of I think a vortex cart, using a 1mb sram replacement , so that's what I was trying to do there. And it did work, but I figured it was a waste to use it instead of the original 256kb chip. Incidentally, the ROM that is currently installed, which worked on the 1mb is the starfox competition instead of the regular starfox. But as I say, I tried replacing it with the 1mb again just to be sure and it did the same, so I don't think it's the ROM.

Ah, I see. So they don't actually do anything then? I see a few dummy hole endings too, so it seems to have both.

I think I'm just gonna have to write it off for now, admittedly it's only a £5-£10 game, so it's not too bad, but it's a shame, since I did have it working before I replaced the original sram chip. I just can't see anything wrong, beyond the burns. Everything seems to connect up just as it should.


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PostPosted: Wed Mar 27, 2019 12:34 pm 
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The small holes are via's (connections to the opposite side of the board). I meant bigger holes with dummy deadend wires, like on this board https://snescentral.com/pcbboards.php?c ... 1CA0N6S-01 near mask rom.

Okay, then the sram is wird okay (but you did see what I meant, the short wire appearing to be wired to the right pin on the photo, where it's actually supposed to go tomthe left pin).

To deacrivate a chip, without removing it: You could simply wire the /CS chip select to VCC, and cut the connection to where the original /CS signal came from. Then you can wire all signals for your new memory chip piggyback on the old memory chip (except the /CS pin, of course).

If the sound upload is working, but video shows only garbage... Yes, problem might be SRAM not working and causing the code in ROM to crash, or wiring for upper ROM addresss lines is bugged (in case sound needs only the lower addresses), or the MC1 as a whole may have died somehow.


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