The Commodore 64 power supply connector (designated CN7 in Commodore service documentation) is a 7-pin male DIN socket mounted on the C64 motherboard. It accepts an external linear power brick (part number C 251053-02) and delivers two supply rails: +5 VDC regulated for logic circuitry and 9 VAC unregulated, which the onboard regulators rectify to produce +12 VDC (via VR1 MC7812CT) for the SID and VIC-II chips and an additional regulated +5 V rail (via VR2 MC7805CT). Although the connector has seven pins, only four carry active signals; the remainder are tied to ground. The PSU brick’s internal 5 V linear regulator is a known failure point: should it fail open, the full rectified 9 VAC supply (approximately 12 V) appears on the +5 V rail and destroys the SID, RAM, and other chips.
7 PIN DIN ‘C’ FEMALE at the computer.
| Pin | Name |
|---|---|
| 1 | GND |
| 2 | GND (5V negative pole) |
| 3 | GND |
| 4 | nc or +5V in |
| 5 | +5V in |
| 6 | 9VAC in |
| 7 | 9VAC in |
Signals
- GND — Ground reference; pins 1, 2, and 3 are all connected to ground on the C64 PCB.
- nc or +5V in — Pin 4 is either not connected or tied to +5 VDC depending on the PCB revision; it carries no additional load in normal operation.
- +5V in — Pin 5 is the primary regulated +5 VDC supply from the external brick, used by all TTL and CMOS logic on the board.
- 9VAC in — Pins 6 and 7 carry the 9 VAC unregulated secondary from the PSU transformer. This AC supply is rectified and regulated on the C64 motherboard to derive +12 VDC (for the SID and VIC-II) and a secondary +5 V rail. The same 9 VAC is also routed to the User Port (CN2, pins 10 and 11).
Notes
The connector is a 7-pin round DIN in the large “Type C” shell. Only four of the seven pins are electrically active; the remaining three are grounded. The external PSU (C 251053-02) is a linear brick — not a switching supply — and its onboard 5 V regulator is unreliable with age. The PSU should be tested before connecting to a C64: a failing regulator can allow the full rectified 9 VAC (approximately 12 V) to appear on the +5 V rail, causing irreversible damage to the SID, RAM, and CPU. The 9 VAC supply from the PSU is used exclusively by the onboard regulators; +12 VDC is generated internally and is not supplied directly by the brick.