A Moogle  🏳️‍🌈 💻 🎮 🎶 🇸🇪

tell me where, I've got 50 Famicoms to refurb.

@furrtek @plgDavid Yes, it probably would help, but my suspicion is that it would be at the cost of frequency response. What you more likely want is a notch filter for the frequency which is intruding on the final video signal.

But how would the notch filter distinguish between the parasitic signal and graphics that produce the frequency ?

Sorry, I only saw the initial screenshot in the thread, not the subsequent tweets. That said: The jailbars seem to be about 1 cycle per tile. That's far lower than any signal that'd be getting thrown around the Famicom's internal buses. Tuned properly, it could work.

I was thinking more along the lines of something that could be connected in-line with the Famicom's video output in order to mute the jailbar effect. Given the NTSC color burst frequency, notching out a frequency of 1 cycle per tile shouldn't affect the eventual output.

From what I can tell, the SRAM seems to be parasitically pulling a couple milliamps off of the the bus, which leads to cycles of voltage dropping (increased luma) across the raster, one per nametable square at the beginning - corresponding with nametable CIRAM fetch by the PPU.

Perhaps the most noninvasive strategy involving the output signal would be to introduce a comb filter instead of a notch filter, tuned in such a way to repeat the low-frequency luma component in the pre-bar zone in the raster but not the high-frequency chroma subcarrier.

I believe in fixing the issue at the source, by providing the ICs all the current they need even when they pump like crazy using carefully chosen capacitor values and placement?