315-5242 colour encoder reproduction

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    • 315-5242 colour encoder reproduction

      Hi all,

      I've been finally hit by the failure of that custom module. It's used on many Sega boards (X board, Y board, Systems C/C2/18/24/32) to increase palette.

      Since I don't have the tools to decap one I simply pulled a good one and studied it on the bench. It's rather simple (mainly latches and resistors to form a DAC). Only thing I'm not 100% sure of are resistors exact values. I set my PSU to +5.00V and measured voltage before and after the final amplification stage transistors then deducted resistors values for the DAC. One thing I've learned is you can get rid of the transistors by using appropriate resistors values. Sega used much higher values inside the on the module, I guess to limit power dissipation since they are film resistors.

      I've made a first repro on a piece of breadboard (a bit shitty since its a SDIP device) and will release gerbers and BOMs here as soon as they're ready.



      J1Connector2*32p 0.7" strip pin
      U1, U2IC74LS273SOIC20, 300mil
      U3IC74LS74SOIC14, 150mil
      U4IC74LS125SOIC16, 150mil
      C1~4Capacitor100nF ceramic, 0805 footprint0805 footprint
      R1, R7, R13Resistor4K, 0805 footprintCan be substituted by a rounded value of 4,7K
      R2, R8, R14Resistor2K, 0805 footprintCan be substituted by a rounded value of 2,2K
      R3, R6, R9, R12, R16, R18~21Resistor1K, 0805 footprint
      R4, R10, R16Resistor500R, 0805 footprintCan be substituted by a rounded value of 470R
      R5, R11, R17Resistor250R, 0805 footprintCan be substituted by a rounded value of 220R



      Looking for:
      - faulty Space Harrier or Enduro Racer
      - Sega Mega-CD 1 power board
      - Super Nintendo CPU (3 needed)

      "I'd 1cc games but I have a real life."
      01010011 01000101 01000011 01010010 01000101 01010100 00100000 01001101 01000101 01001110 01010101 00100000 01000111 01010101 01011001

      The post was edited 3 times, last by Apocalypse ().