Repair & Schematics
SNES

RGB Video Cleanup (SNES)

7min

There are many revisions of SNES and many video related issues that need fixing.

Below will be a list of fixes for all console revisions that need it, and how to fix each issue.

SHVC-CPU-01

This revision can get perfect RGB output with zero faults with the fixes below.

Ghosting / Blurry edges

The blur at the edges of pixels from left to right is caused by an inherent low-pass filter inside the PPU2. This can be corrected and sharpened up with the EdgeBuster we sell.

Vertical Center Band & Moving Checkerboard Pattern

This is caused from what I have gathered so far in relation to the data bus.

If you add back data bus traffic to the output video signal using a 47k resistor to super-impose it, you will see the distinctive vertical band and random noise patterns.

Moreover, if you go to 240p test suite homepage and scroll up and down you will see the grey background react to the data bus change.

I have yet to find a solution to remove this noise but will add it here once solved.

Small Vertical Bars

Present on the SNS-CPU-GPM-02 revision, these bars only really become visible once you fully clean up and sharpen the RGB output with EdgeBuster and CleanRGB for example. If your output is not super sharp and crisp you won't see them.

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This is caused by the DRAM as it is related to the data specifically. In 240p test suite the background grey will show it the most, but generating the same grey color in the test screen won't show it, proving its data related.

I suspect the best fix will be to lift the 5V on the WRAM (DRAM) chip and power it from a separate regulator perhaps.

Static Checkerboard Pattern

This is caused by the chroma clock (3.58MHz) on PPU2 pin 3, and Dot Clock (!5MOUT) on PPU2 pin 27.

NOTE: You will not see this static checkerboard pattern until you fix the vertical center band and moving checkerboard pattern which are much stronger interference.

Underneath PPU2 are the traces in question that add noise to the RGB traces.

Purple is the 5MHz clock, and yellow is the 3.58MHz clock.

You can see they run alongside the R and G traces.

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Cut the chroma trace at the start and at the end where it meets R29, and then solder a wire between the two points, bypassing the original trace.

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For the 5MHz clock, just turn the resistor, attach a wire, then cut the trace at the end where it meets the R38 empty pad, and then solder a wire between the two points, bypassing the original trace.

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