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Thread: SNES / SFC SHVC-CPU-001 2-chip RGB filter mod video fix

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    SNES / SFC SHVC-CPU-001 2-chip RGB filter mod video fix

    NOTE: Mod is now tested and works well for SFC! I'm not sure it will work properly for a PAL SNES however. Anyone want to try it?

    A little while ago someone posted a link to a Super Famicom/SNES video filter mod I thought I’d try my hand at. It’s supposed to bring the RGB video output of a SHVC-CPU-001 (initial version) SNES more in line with the quality of a 1-chip model. This is by Japanese modder Torapu, all I did was lay out the PCB, after working out what he actually did compared to what he wrote (i think). It's worth taking a look at Torapu's site for the expected results too, though i have some below.

    Torapu’s page on the mod, including his mostly-complete schematics. I stole a lot of his photos to make life easier - https://translate.google.com/transla...sfc_sharp2.htm
    Shmup’s thread on the mod - https://shmups.system11.org/viewtopi...=give#p1374468
    SNES revision 2 schematics (very similar to the SHVC-CPU-001 used in the mod) - https://wiki.superfamicom.org/upload...atic_color.pdf

    I’ve put the gerber PCB files on OSH park, from where they can be downloaded. Note that the printed board is about 34mm x 27mm using mostly surface mount devices so the soldering is not ideal for beginners. This board is a first cut, it works fine but the tracks are not tuned for length or any possible interference.

    Parts:
    • All diodes are DO-35 package 1S2076A. Each set is two diodes, one forwards one backwards.
    • U1 is a LMH6683MAX package SOIC14.
    • You can recycle three 2SA1037A package SOT-346 transistors from the SNES mainboard, or buy new ones.

    All other packages are 1206 size:
    • 2kR - R2, R3, R12, R13, R19, R20
    • 300R – R1, R14, R21
    • 200R – R4, R5, R10, R11, R17, R18
    • 47R – R6, R7, R8, R9, R15, R16
    • All caps 1nF


    Method:
    • On the bottom side of the SNES mainboard itself, caps C83, C92, C94 should be replaced with 10uF. 1206 package size caps will still fit ok.
      CIMG2626.jpg
    • The new filter board will sit in the bottom left of the photo above. It should be insulated from the SNES mainboard. Securing it with double-sided tape would be appropriate.
    • On the new filter board, Q3, Q5, Q7 are 2SA1037A, SOT-346. These can be taken from the positions with the same name on the SNES mainboard or you can get new ones, and either way those transistors must be removed from the SNES mainboard. No other components should be removed from the SNES mainboard.
    • The filter board pads Q3-E, Q3-B, Q5-E etc should be wired to the SNES main board at those positions, after Q3, Q5, Q7 have been removed.
    • On the filter board, GND from the SNES mainboard can be connected near the bottom left of the daughter board. See pic below. Only a single ground connection should be made.
    • On the filter board, +5V can be connected from the SNES mainboard at the lower side of R7, R12 or R17 (the end toward the "R" in each case) among many other spots. See the first photo above. I think i grab it from the lower side of the replaced C92 in the pic below.
    • On the SNES mainboard, 270pF caps are required between Base and Collector of Q4, Q6, Q8 (one for each transistor)
      CIMG2718.jpg
      CIMG2730.jpg


    Install Pics:
    Note the single ground wire in the bottom left corner of the daughter board, it's in black and not easy to see in the shadows. I scratched off the surface coating of the mainboard to anchor it the other end.
    DZugPI5.jpg
    The daughter board is stuck on the mainboard with double-sided tape, and i then added some electrical tape lining the bottom RFI shielding to prevent any possible contact with it.
    X5vt7UV.jpg


    Results:
    Well, i actually got around to completing the mod, and it seems to work pretty well. I haven't tried too many different test screens yet, and will hopefully update in a few days when i get time. And maybe with some pics, but i can't shoot CRT for shit... but here goes anyway...

    This is a shot of the difference on my Ikegami TM10-17RA 10" shadow mask CRT. The example is black to grey, but all colour transitions from primary to half-tone and vice versa are affected. The full size version of the below pic is here

    d9hJQWa.jpg

    Please note those photos are terrible, and in reality the difference is more marked. It's still not perfect but the image is noticeably clearer and also a shade brighter and more colourful without crushing either the blacks or the highlights. If you compare the before and after images it might be said the before image is slightly "muddier."
    Last edited by buttersoft; 14 Hours Ago at 02:46 PM.

  2. #2
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    Holy Crap, it works! And works well.

    I'll update the OP in a couple of days when i get time.

    EDIT: And i totally forgot to add the 270pf filter caps on Q4, Q6 & Q* too! Might not even bother now.
    Last edited by buttersoft; 3 Days Ago at 09:28 PM.

  3. #3
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    Photos are up They don't really do the mod justice, i found the difference pretty noticeable. The pics are meant to highlight a single transition, but any full-colour picture is made up of such smaller transitions, and so the whole image gets slightly smeared. The mod fixes a lot of that.

    EDIT: I should probably be clear about the fact that i've only tried this mod on an SFC. An NTSC SNES should work ok, but i'm not sure about a PAL SNES> If anyone wants to try it, please report back
    Last edited by buttersoft; 1 Day Ago at 11:32 AM.

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