NES Graphics Issues

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merakione77
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NES Graphics Issues

Post by merakione77 » Tue Feb 12, 2019 3:45 am

Hi All,

I hope this is in █a delicious SUBWAY® sandwich for a reddit copycat█, but to make this short- I’m running into an issue with my NES (VCR style, not top loader). When I start up any game, everything works fine, but after some time passes, the sprites will flicker and then half of the sprite will disappear and populate on the right-hand side of the screen in just black and white. [Link spam removed]
If I shut it off and turn it back on, the time before the sprites split shortens and so on and so forth. I’ve tried both boiling and replacing the 72 pin with little success. Any insight as to how I can fix this? Is it an SRAM or PPU problem? I’m semi-proficient soldering if need be! Thanks in advance!
Last edited by merakione77 on Fri Feb 15, 2019 1:04 am, edited 1 time in total.

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pubby
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Re: NES Graphics Issues

Post by pubby » Tue Feb 12, 2019 4:18 am

I'm just a software guy but it sounds more like a bad PPU than bad SRAM . It probably malfunctions when hot - have you tried cooling the PPU while its running?

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tokumaru
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Re: NES Graphics Issues

Post by tokumaru » Tue Feb 12, 2019 4:42 am

Sprite positioning information is kept in memory inside the PPU itself, so this is most likely a PPU issue.

lidnariq
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Re: NES Graphics Issues

Post by lidnariq » Tue Feb 12, 2019 10:37 am

merakione77 wrote:If I shut it off and turn it back on, the time before the sprites split shortens
Not only is it the PPU, but it's thermal. You might just be able to get away with adding a heatsink or other cooling to the PPU.

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tokumaru
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Re: NES Graphics Issues

Post by tokumaru » Tue Feb 12, 2019 11:12 am

lidnariq wrote:You might just be able to get away with adding a heatsink or other cooling to the PPU.
Wouldn't that be a short-term solution though? The fact that the PPU is overheating is a sign that something isn't right, isn't it?

lidnariq
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Re: NES Graphics Issues

Post by lidnariq » Tue Feb 12, 2019 11:44 am

Not really? There's no particular reason to think that the underlying problem would be progressive, or that if it were progressive, that the die temperature wouldn't be decreased enough by an external passive heatsink to prevent more damage.

I mean, yes, it is sign that Something Is Wrong™ but you aren't gonna fix it in the field, and a bodge is good enough. We also know that the oldest versions of the PPU had heat spreaders.

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Fisher
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Re: NES Graphics Issues

Post by Fisher » Tue Feb 12, 2019 3:02 pm

Interesting.
I've found some RGB PPUs with heatsink, are the old verions similar?
post-8695-0-49693300-1364429640.jpg
I also have found a (very bad) picture of heatsinks attached to the CPU and PPU of an NES clone:
11_boardready.jpg
Maybe one of these little "mods" can help?

Any chance of being a power supply problem or other component?

lidnariq
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Re: NES Graphics Issues

Post by lidnariq » Tue Feb 12, 2019 3:55 pm

Fisher wrote:I've found some RGB PPUs with heatsink, are the old versions similar?
Yeah, older versions of the 2C02 also have heat spreaders.

e.g. this picture
http://offgao.blog112.fc2.com/blog-entry-15.html
http://offgao.blog112.fc2.com/blog-entry-15.html

The behavior as described is definitely thermal. While's conceivable that it could be the power supply, I'd definitely suspect the PPU first.

... also, unrelated, I wonder if RP2C02 vs RC2C02 is Plastic vs Ceramic package.

krzysiobal
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Re: NES Graphics Issues

Post by krzysiobal » Wed Feb 13, 2019 9:56 am

Check the voltage when PPU starts displayin garbage. When 7805 becomes too hot (poor heatsink, something other draws too much current), it lowers the voltage. PPU is very sensible to correct voltage - if it gets too high, some colors will not look propery. If it gets too low, might start displaying junk.

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Ben Boldt
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Re: NES Graphics Issues

Post by Ben Boldt » Wed Feb 13, 2019 3:15 pm

Check for bad capacitors, especially the large capacitor at the back right corner. The top of it should be flat and not rusty, crusty, or domed up at all. If it is original, you should replace it anyway, it is a cheap and easy thing to try.

tepples
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Re: NES Graphics Issues

Post by tepples » Thu Nov 14, 2019 1:02 pm

Locking for three reasons:

1. uses "sub" which is Reddit terminology, not ours
2. had stealthy link spam added (using the color tag)
3. someone later posted an exact duplicate topic, which I also locked

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