C64 Assembly 250466

  • Released in 1986.
  • 8-pin board (Reduced Oscillator Circuit).
  • Version: B-3.
  • Schematic Number 252278.
  • Last of the “Bread Bin” Models.
  • Identical to previous designs except for the two 64 kilobit × 4 bit DRAM chips that replaced the original eight 64 kilobit × 1 bit ICs.

Specs

  • CPU : 6510 @ 1.0227277143 MHz (NTSC) / 0.9852484444 MHz (PAL)
  • RAM : 64kB DRAM
  • ROM : 20kB ROM Total - 8K BASIC, 8K Kernal, 4K Character
  • Graphics : VIC-II
  • Sound : SID
  • Interfaces : 2 Control Ports (CIA U1), A/V, Datasette Port (CIA U1), Expansion Port, Serial IEC (CIA U2), TV RF, User Port (CIA U2)
  • Keyboard : 66 Keys (CIA U1)
  • Power Supply : External Transformer (9V AC + 5V DC)

Schematics

Fig. 1: C64 250466 Mainboard Fig. 2: C64 250466 Layout

Capacitor List

Cap   -  Value   - Rating - Type
C13   -  10uf    -  25v   - Radial
C19   -  2200uF  -  16v   - Axial
C24   -  22uf    -  25v   - Radial
C88   -  1000uF  -  25v   - Axial
C90   -  470uF   -  25v   - Axial
C91   -  100uF   -  16v   - Radial
C200  -  2.2uF   -  50v   - Radial

C38   -  4.7nf   -   *    - Ceramic

* Replace the 51pf cap with a 4.7nf cap to restore soft-touch RESTORE key function. This is included in our kit.

IC List

PCB ID Chip ID Notes
U1 6526 CIA 1
U2 6526 CIA 2
U3 2364 ROM - Basic
U4 2364 ROM - Kernal
U5 2332 ROM - Char
U6 2114L-30 SRAM
U7 6510 Processor
U8 7406/7416 Logic NOT
U9 44164 DRAM 64Kx4
U10 44164 DRAM 64Kx4
U13 74LS257 Multiplexor
PCB ID Chip ID Notes
U14 74LS258 Multiplexor
U15 74LS139 Demultiplexor
U16 4066 Quad Bi-Switch
U17 82S100 PLA
U18 6581 SID
U19 6567/6569 VIC-II
U20 LM556 Dual Timer
U25 74LS257 Multiplexor
U26 74LS373 8 Bit 3-State Latch
U28 4066 Quad Bi-Switch
U31 8701T6/L6 Oscillator

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