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PostPosted: Sat Apr 22, 2017 10:36 pm 
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Sorry to to post this in here as it seems this forum is way beyond this amateur issue, but it's the only site I've found with decent info.

I recently received a front loading NES with replaced 72 pin that I bought off of ebay. When I turn the power on I get the game's title screen like normal, but the menus have no cursor like normal. When playing Tetris the game screen shows like normal, but I can't see any of the blocks until they reach the bottom. I can turn them and hear all the sound associated with moving and turning them, but can't see them until they land. Also when playing the Mario brothers arcade game I can't see Mario or any of the turtles or coins. I can jump and bend the blocks and hit the "pow" block, but can't see any of the moving characters.

Those are the only two games I've got to try, but I figured it's unlikely that both games would have the same issue. Just wondering if it's something that could possibly be easily fixed or if I should just return the console and try again.

Thanks in advance for any info.


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PostPosted: Sat Apr 22, 2017 11:06 pm 
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Without any other glitches, I have to admit that I can't think of a way that particular symptom would appear in a way that would be repairable...


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PostPosted: Sat Apr 22, 2017 11:07 pm 
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The issue sounds like no sprites are being shown and only the background layer. There could be multiple potential causes for this. First you should clean the game cartridges if you can. Just because the connector has been replaced doesn't mean you don't have to clean the cartridges. If you have the appropriate bit to open the cartridges or they have flat blade screws you can open them up to clean them. If you choose to open them you should ground yourself/discharge any static electric charge before handling the board just to be safe. To clean the cartridge contacts you can use a soft pink pencil eraser. Just be sure to wipe away any debris with a dry paper towel afterward.

If cleaning doesn't seem to help then you might move on to checking other causes. It also wouldn't hurt to pickup some other cheap cartridges to try. The more you can test and tell others about the specific things going wrong the more likely someone can theorize what is wrong.

But from what you described so far it sounds like your sprites aren't showing up at all. I don't know all the possible things that could cause that. But cleaning is a good start.


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PostPosted: Sun Apr 23, 2017 2:44 am 
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I have 200+ NES games, and haven't once seen a game that refused to display sprites entirely due to a bad connection. Usually you just get garbled tiles or nothing at all. For it to happen on two out of two games, I'd say that's a pretty fair indicator that the problem is in the NES, and unrelated to the new cartridge connector.

Did you try the games before replacing it and see them work correctly? If they did, something must have broken during installation, but I honestly think this sounds more like a problem you'd just get from old used up components, most likely a capacitor somewhere on the PCB (it's usually fairly visible if they are in a bad shape). Unless faulty PPU's is a known thing on NES?

edit: Actually, I guess a broken pin somewhere on PPU A0 to PPU A13 could prevent access to one of the pattern tables of the CHR ROM, though I doubt that would result in simply invisible sprites? Could be interesting to test with a game which uses reverse background/object layout in CHR, or sprites from the BG patterns in 8x16 mode.


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PostPosted: Mon Apr 24, 2017 11:17 am 
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I guess a dirty connection wouldn't make sense for a clean no sprites appearing effect. More games tested and pictures would help with diagnosis. It could just be when they replaced the connector they damaged something or static electricity zapped the PPU. It would be a pretty weird failure to have sprites perfectly missing and not garbage.

Since you have a limited time to return the unit I would say return it and get a new unit. If the PPU is actually damaged there is no fixing it.


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PostPosted: Mon Apr 24, 2017 12:52 pm 
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If you have Super Mario Bros. 3, test that game before returning your NES. It stores backgrounds and sprites in the opposite regions compared to Tetris and Mario Bros.. If the sprites still don't appear, then it's probably a bad PPU. If only the sprites and no backgrounds appear, then I have no idea what could have gone wrong; bad pins usually result in corrupted graphics, not missing graphics entirely.


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PostPosted: Mon Apr 24, 2017 5:14 pm 
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That is really strange. I suppose you could try taking it apart, remove and re-install the connector. But not if that will give the seller cause to not take a return, just depends on the what the seller prefers at this point.

This reminds me of the time I found a boxed, mint condition Atari 2600 at Goodwill. I took it home, then every game I tried on it there were no player (sprite) graphics, but the playfield (background) graphics were fine. Very weird, had to be a bad TIA chip. NES is quite different in that the video memory is on the cartridge, so the problem you're having sounds almost plausibly like a connector issue. But I don't know, it doesn't sound too hopeful.. normally you would expect to see garbage graphics.


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PostPosted: Mon Apr 24, 2017 7:56 pm 
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I can't think of anything plausible other than a bad PPU. There's no easy way to disrupt sprite fetches and only sprite fetches. A shorted trace would just give you garbled graphics rather than missing graphics. The replaced 72-pin connector may be a red herring, it could be that this NES was on eBay because of the missing sprites rather than the replaced 72-pin connector. :P

If this was specifically someone offering a service of reselling refurbished NESes, try contacting them and see if you can send it back for a new one. If this was someone just selling a random odd NES, I think the missing sprites were why it was on eBay. You'd need to replace the PPU (the graphics chip) in order to fix this issue, but since the PPU is a custom part and not something you can just buy in bulk, you'd have to salvage one from another working unit, and when you're at that point, you'd might as well just buy the working unit. :P


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PostPosted: Mon Apr 24, 2017 8:14 pm 
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The only connection I can see between this and the connector is that DMA has slightly different memory access timing from the rest of the CPU's memory accesses. I seem to remember the PowerPak having DMA trouble when it first came out.


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PostPosted: Mon Apr 24, 2017 11:53 pm 
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That's an interesting theory. Do we know of any games that -don't- use DMA to write to the OAM?


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PostPosted: Tue Apr 25, 2017 12:03 am 
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No, because it's too slow.

Magic Floor is more-or-less it, and because of bugs in the 2C02, it only works correctly with the PAL 2C07.


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PostPosted: Tue Apr 25, 2017 12:42 am 
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Another thought - does sprite 0 hit work? That could reveal wether the game -thinks- it's drawing the sprite, or doesn't know about the sprite entirely.
Basically, does SMB1 freeze when you start the game, or does it scroll as it should.


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PostPosted: Tue Apr 25, 2017 7:11 am 
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Alternatives to the PPU being bad internally:
-is it getting enough current? Is the power supply correct and allright?
-there's a slim chance reflowing the solder points on the data lines between PPU and things it is connected to might help.

If you can't get a refund, you can keep or sell it as spare parts, worst case.

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PostPosted: Tue Apr 25, 2017 8:40 am 
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I have a Famicom with a bad PPU like yours. The sprites more or less do not work. They appear scrambled on the left side of the screen, at one of four Y positions. Totally broken.

The PPU is also very warm to the touch; something is upset in there.


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PostPosted: Fri May 12, 2017 8:11 am 
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Sounds like a bad PPU to me. But theoretically it could (higly unlikely) be a bad connection in a very specific way.

I have a NES that will only display 7 sprites on a scanline. Maybe yours is similar, but with 0 :)


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