Commodore 64C

Commodore 64C

Commodore 64C with a 1541-II drive and 1084S monitor
Specifications
Manufacturer	Commodore Business Machines
Type	Home computer
Released	1986
Discontinued	1994
CPU	6510 (B-3 board) or 8500 (E board)
Memory	64 KB RAM; 20 KB ROM
Storage	1530 Datasette; 1541 floppy disk drive
Display	320 × 200 pixels; 40 × 25 text; 16 colours
Sound	6581 or 8580 SID
Graphics	VIC-II
Power	External supply: +5 V DC and 9 V AC on a 7-pin DIN
OS / Firmware	Commodore BASIC 2.0 and KERNAL in ROM
Predecessor	Commodore 64
Model no.	C64C

The Commodore 64C is the Commodore 64 in a flatter case, sold from 1986. It runs the same software and uses the same peripherals. Commodore built it on two boards: the B-3 (assembly 250466), which keeps the original chip set with two 64K × 4 DRAMs, and the E (250469), which combines BASIC and KERNAL in one ROM and replaces the PLA with a memory controller.

Boards

C64C board identification

Version	Identifying factor (Commodore)	PCB assembly	Schematic
B-3	Only two RAM chips, U9 and U10	250466-01	252278
E	KERNAL and BASIC ROMs combined into U4; new IC memory controller at U8	250469-01	252312

Commodore's identification table and the caption of the B-3 board layout print the B-3 assembly as "250446"; the parts list heading, and the assembly number printed on the board in that layout drawing, give 250466. The E board also has only two DRAMs (U10 and U11), so the RAM count does not tell the boards apart: the B-3 keeps separate BASIC and KERNAL ROMs at U3 and U4 and the PLA at U17. The long boards (326298, 250407, 250425 and 250441) are listed under C64 identification, not C64C. The E board's layout page gives PCB number 252311.

E board chips

250469-01 integrated circuits

Position	Part	Commodore part no.
U6	8500 CPU	318012-01
U7	VIC-II, listed as 8567 or 8562	318014-01 / 318027-01
U9	SID, 8580 or 6581	318013-01 / 906112-01
U1, U2	6526 CIA	906108-01
U8	Memory controller	251715-01
U4	128K ROM (BASIC and KERNAL)	251913-01
U5	2332 character ROM	901225-01
U10, U11	64K × 4 DRAM	390083-07
U19	2114 colour RAM (200 ns or 150 ns)	901453-07 / -09
U20	8701 clock generator (8701T6 or 8701L6)	251527-08 / -09
U3	74LS08	901521-03
U22	7406 or 7416	901522-06 / -14
U23	74LS14	901521-30
U18, U21	4066	901502-01

The colour RAM is a separate 2114 at U19, labelled COLRAM on schematic 252312; it is not inside the memory controller.

Clock and video

On the E board, the 8701 clock generator (U20) runs from crystal Y1 with trimmer CT-1 (7.7-40 pF). The schematic notes give Y1 as 14.31818 MHz for NTSC and 17.734472 MHz for PAL, and the dot clock as 8.18 MHz NTSC and 7.88 MHz PAL; jumper J3 is open for NTSC and shorted for PAL. Divided by eight, the dot clock gives the processor clock of about 1.02 MHz (NTSC) or 0.985 MHz (PAL).

The display specification is the C64's: 40 × 25 text, 16 colours, 320 × 200 pixels, and eight sprites of 24 × 21 pixels with up to four colours each and collision detection. On schematic 252312 the VIC-II's VDD pin (13) is connected to +5 V.

The address map is the C64's; see Commodore 64.

Sound and the SID supply

The E board was built with either SID. Its supply comes from transistor Q5 and zener CR7, fed from a raised supply on C66; the schematic labels the output "+9/+12" and also feeds it to the audio buffer transistor Q3. The notes to schematic 252312 set the parts that depend on the SID:

SID-dependent parts, schematic 252312 notes

Part	With 6581	With 8580
CR7	12.6 V zener	9.6 V zener
C70, C71 (SID filter capacitors)	470 pF	22000 pF
C80, C81	1800 pF	2200 pF
R8	Fitted	Removed

Swapping one SID type for the other on an E board means changing all four. An 8580 left on a board set up for a 6581 runs from the 12.6 V zener's supply.

Power

The 64C uses the same external supply as the C64: regulated +5 V DC and 9 V AC on a 7-pin DIN. On the E board, pins 4 and 5 carry +5 V through the power switch, pins 6 and 7 carry 9 V AC (pin 7 through fuse F1, 1.5 A), and pins 1, 2 and 3 are ground. Bridge CR2 and C63 make the 9 V unregulated supply; C65, CR3 and CR4 produce the higher supply on C66 for the SID regulator. The E board has no 7805 or 7812. The B-3 keeps the long boards' VR1 (MC7812CT) and VR2 (MC7805CT).

A note on schematic 252312 gives a French version with a 20 Ω resistor at R2 and a 2200 µF capacitor at C63 (1000 µF otherwise).

Ports

The ports are those of the C64: cartridge expansion port, serial bus, user port, cassette port, two control ports, RF output and the 8-pin audio/video socket. On the E board the audio/video socket (CN5) carries luminance on pin 1, audio out on pin 3, composite on pin 4, audio in on pin 5 and colour on pin 6.

Maintenance and faults

Commodore's troubleshooting table, written for the long boards, lists the external power supply first for a blank screen at power-up, a white or black band scrolling through the picture and a wavy screen after warm-up. The supply's +5 V feeds the logic directly, so a supply that fails high damages the machine; the C64-Wiki treats more than 5.2 V as a failing supply. Measure it before anything else. See Commodore 64 Power-Supply Protector (C64 Saver) for an over-voltage cut-out and PLA Replacement Options for the long and B-3 boards' 82S100 PLA.

• Commodore 64C General Maintenance
• Commodore 64C Troubleshooting Guide
• Commodore 64C Capacitor Replacement Guide (E board) and Commodore 64 Capacitor Replacement Guide (B-3 board)

Gallery

• 
  Commodore 64C, front
• 
  Rear panel
• 
  250469 (E) board, PCB 252311

Related pages

• Commodore 64 · Commodore 128
• Commodore 64C General Maintenance · Commodore 64C Troubleshooting Guide · Commodore 64C Capacitor Replacement Guide
• Commodore 64 / 64C Service Manual
• Commodore 64 Power-Supply Protector (C64 Saver) · Commodore Test Cartridge Index · Recommended Tools