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PostPosted: Sun Dec 09, 2018 8:45 pm 
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I've noticed that regardless of the project I copy to hardware I notice fuzzy-like tearing artifacts for a few seconds after I start the program on an NES. The best way to describe it is like an old dirty VHS tape. Random spots on the picture start to tear a little with a bit of white fuzzyness. It seems no matter how simple or complex the project is, this always happens, even displaying a static nametable with no sprites on screen. Anyone ever experience something similar?

I'm using 16KB eproms and boards from https://www.game-tech.us/ with a TL866II programmer.

Attached shows the programmer settings I'm using which are default. M27128A chip type is also selected.


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PostPosted: Sun Dec 09, 2018 9:31 pm 
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You say the problem goes away after a few seconds? It does this on multiple systems, or just the one you have? Sounds pretty weird, either way. I don't have a Repro-X board to check, if you're using a 16kB EPROM, what is CHR-ROM A13 connected to?

Closest thing I've experienced is on my front-loader, the audio volume would be low for the first 5-10 seconds after powering it on. Was very noticeable when I started using it a few years ago, but it seems to have gone away over time. I guess the caps are bad.


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PostPosted: Sun Dec 09, 2018 10:12 pm 
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Yeah it seems to clear up after a bit. It may return some time later but the picture does clear up. My CHR is 8KB and I'm doubling this twice for the CHR chip. I failed to mention the NES unit I'm using currently is the AVS, though I have not seen this with other games.


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PostPosted: Mon Dec 10, 2018 8:42 pm 
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Even though the 8kB ROM is doubled and the data would be the same, the unused address input should still be connected to something. 5V, GND, or another address line is fine. Does your cart have bypass capacitors as well?

Pretty interesting that it's the AVS. That's all digital, not really where one would expect to see noise.


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PostPosted: Tue Dec 11, 2018 9:15 pm 
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I have some capacitors on it, pics below of front and back.

By unused address input are you referring to pads on the board that extend beyond the amount of pins I have? Should I just put some solder on that? (would that be grounding it?)

Besides the random fuzzy tearing the programs run pretty well. Today I was running some more tests on a game of mine and there were a couple startups where the fuzzy-ness didn't appear. Very random but definitely off somewhere.


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PostPosted: Wed Dec 12, 2018 4:06 pm 
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I was referring to A13 on the CHR-ROM. Pin 26 on the 27C128, based on the the pics it looks like it may connect to the uninstalled mapper chips. If that's true, what I would do is short it to pin 27 or 25. An unconnected input like that can pick up whatever magnetic fields (EMF) are in the area and might end up rapidly changing between 0 and 1 state. I don't know if that would fix the problem, but it would be the proper way to hook up the EPROM.


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PostPosted: Wed Dec 12, 2018 10:04 pm 
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what I would do is short it to pin 27 or 25


I have a very noob-y question, but by short do you mean just bridge the two pins together (like 26 and 27)?

I added a clearer photo of another board without a chip in.


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PostPosted: Wed Dec 12, 2018 11:01 pm 
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casprog wrote:
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what I would do is short it to pin 27 or 25


I have a very noob-y question, but by short do you mean just bridge the two pins together (like 26 and 27)?


Yeah, exactly.


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