Horizontal line glitch in the lower left corner

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Milowork
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Horizontal line glitch in the lower left corner

Post by Milowork »

I made a famicom by myself with perfboard, but the following glitch appeared.
I have tried to adding filter capacitors, connect an external 5V power supply, replace the video memory chip, reverse the PPU clock phase, and replace the CPU, but the fault persists.
Neswires4.png
IMG_20210507_210623_1040.jpg
IMG_20210507_210504_1040.jpg
lidnariq
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Re: Horizontal line glitch in the lower left corner

Post by lidnariq »

What's weird to me is: I think the artifacts in the corner are OAM, not background tiles.

You might try more lower ESR capacitance across the PPU's power pins. Otherwise I fear the PPU is what is damaged.
Milowork
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Re: Horizontal line glitch in the lower left corner

Post by Milowork »

not solved by replacement of ppu
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krzysiobal
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Re: Horizontal line glitch in the lower left corner

Post by krzysiobal »

I don't know where you get your UA6528 PPU, but many of them acquired from China are broken. I wouldn't be surprised if both of your chips are broken.
I built famicom on perfboard years ago and did not have any problems, even without any decoupling capacitors. This is surely something wrong with the OAM RAM inside PPU or the part of PPU responsible for determining which sprite should be evaluated and displayed.
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Ben Boldt
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Re: Horizontal line glitch in the lower left corner

Post by Ben Boldt »

Kind of a long-shot but how does this type of PPU act with Vcc voltage too high or too low? It may be worth measuring right at the PPU pins to double-check.

Seems strange it is worse at the bottom of the picture. Basically everything that it uses at the bottom worked fine up top, as if something sagged on the way down. Adding different size caps directly from VCC to GND of the PPU might be an interesting experiment, could point to a power supply problem or too thin wires, etc.
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aquasnake
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Re: Horizontal line glitch in the lower left corner

Post by aquasnake »

Please confirm whether there is a pull-up resistor 10K on the IRQ line
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TmEE
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Re: Horizontal line glitch in the lower left corner

Post by TmEE »

You need to feed clock to CPU and PPU through series capacitors instead of direct connection. I made 21 and 26MHz oscillators for PAL and NTSC support on one NES I have and it misbehaved until I had used those capacitors on the clock inputs of both PPU and CPU.
Milowork
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Re: Horizontal line glitch in the lower left corner

Post by Milowork »

This is a flaw of my TV, only with NTSC format. No problem when using USB AV capture.
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