Converting a Sega C board to C2

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    • Converting a Sega C board to C2

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      There are few differences between C and C2, obvious one is the lack of sample support but there's more (extended work RAM from 2 * 8kB to 2 * 32kB, etc.).

      1) What are you going to need

      - 2 * 62256 RAM chips (8bit*32kB, DIP28, both 0.3" and 0.6" are accepted)
      - 1 * µPD7759
      - 1 * 640kHz oscillator
      - 1 * 74LS373 (DIP20)
      - 2 * 150pF capacitor (ceramic)
      - 1 * 1.5nF capacitor (plastic film)
      - 1 * 2.2nF capacitor (plastic film)
      - 1 * 3.3nF capacitor (plastic film)
      - 1 * 8.2nF capacitor (plastic film)
      - 3 * 22nF capacitor (ceramic)
      - 1 * 10µF, 50V polarised capacitor (electrochemical)
      - 1 * 1k resistor (1/8W)
      - 1 * 5.7k resistor (1/8W)
      - 2 * 8.2k resistor (1/8W)
      - 1 * 16k resistor (1/8W)
      - 1 * 47k resistor (1/8W)
      - 1 * 75k resistor (1/8W)
      - 1 * 4x4.7k resistor array (SIL9)
      - 2 * 4 header pin (0.1")
      - 1 * DIP32 socket
      - some wire

      2) Steps to follow

      2.1) Pull work RAMs IC29/IC30 and install 62256 devices instead.

      2.2) Move R30 to R31.

      2.3) Install

      IC7 = µPD7759
      RA9 = 4 * 4.7k
      C15 = 22nF
      IC5 = 74LS373
      C12 = 22nF
      JP9/JP10/JP11/JP12 = 0.1" header pins
      IC4 = DIP32 socket
      C11 = 22nF
      C53/C54 = 150pF
      XL1 = 640kHz
      C57 = 2.2nF
      C58 = 1.5nF
      C68 = 10µF, 50V
      C61 = 8.2nF
      C60 = 3.3nF
      R22/R23 = 8.2K
      R15 = 47K
      R16 = 1K
      R12 = 16K
      R13 = 75K
      R14 = 5.7K

      2.4) But that's not all, very few C2 games will work (it depends how they were programmed to "talk" with the YM3438 FM chip, most enter an infinite loop and show a black screen, no sound) unless you do that last step.
      Of course I could patch the games to accomodate the difference but I prefer to go the hardware mod route all the way:
      - Isolate pin 19 of the µPD7759 (reset) and tie it to pin 13 (reset command from IC1, I/O chip 315-5296) of IC23 (74LS08).
      - Isolate pin 11 of the YM3438 (initialise) and tie it to pin 12 (master RESET) of IC23 (74LS08).

      3) Result

      That's it, your C board is now a C2. Was it worth the parts cost and time involved? Surely not...

      If you own/want to install a multi kit here's the jumpers setting:
      JP1 = 1-2
      JP2 = 1-2
      JP3 = 1-2
      JP4 = 1-2
      JP5 = 1-2
      JP6 = 1-2
      JP7 = 2-3
      JP8 = 1-2
      JP9 = 1-2
      JP10 = 1-2
      JP11 = 1-2
      JP12 = 1-2
      JP13 = 1-2

      Basically all 1-2 but JP7 2-3.
      Looking for:
      - faulty Space Harrier or Enduro Racer
      - Super Nintendo CPU (3 needed)
      - Sega trackball I/O board 837-8685 (will be reproduced and gerbers made freely available)



      "I'd 1cc games but I have a real life."
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      The post was edited 2 times, last by Apocalypse ().