Board 250466 B3

250466 (B3)

  • Only 2 RAM chips, U9, U10.
  • PCB Assembly Number 250466.
  • Schematic Number 252278.
  • In 1986, Commodore released the last revision to the classic C64 motherboard. It was otherwise identical to the 1984 design, except for the two 64 kilobit × 4 bit DRAM chips that replaced the original eight 64 kilobit × 1 bit ICs.
  • After the release of the C64C, MOS Technology began to reconfigure the C64’s chipset to use HMOS production technology. The main benefit of using HMOS was that it required less current to drive the IC, which consequently generates less heat. This enhanced the overall reliability of the SID and VIC-II. The new chipset was renumbered to 85xx to reflect the change to HMOS.
  • The modifications to the C64 line were more than skin deep in the C64C with new versions of the SID chips being deployed—with the core voltage reduced from 12 V to 9 V, and the VIC using only 5V. The I/O chips remained functionally identical but the new 8521 which uses HMOS technology uses about half the power of the original NMOS 6526. The basic and kernal 2364 ROMs were also replaced with a single 23128 ROM.

Integrated Circuits

PCB Identifier Chip NumberRemarks Memory Location/bit
U1 6526
CIA 1$DC00-$DCFF
U26526
CIA 2$DD00-$DDFF
U32364Basic ROM$A000-$BFFF
U42364Kernal ROM$E000-$FFFF
U52332Character ROM$D000-$DFFF
U62114L-30 SRAM 1Kx4$D800-$DBFF
U76510
CPU
U87406Logic NOT (Hex Inverter)
U941464 DRAM 64Kx1D4..D7
U1041464DRAM 64Kx1D0..D3
U1374LS257Multiplexor
U1474LS258 Multiplexor
U1574LS139 Demultiplexor
U164066Quad Bilateral Switch
U1782S100 / 906114-01
PLA
U186581
SID$D400-$D7FF
U196567 (NTSC)/6569 (PAL)VIC-II $D000-$D3FF
U20LM556 Dual Timer
U2574LS257Multiplexor
U2674LS373Multiplexor
U284066Quad Bilateral Switch
U317701/8701Oscillator

Schematics
252278-1
252278-2
Board Image
board 250466