Power Mac G4 - 22 pin Power Supply Connector
The Apple Power Mac G4 uses a proprietary mainboard power connector that is not electrically compatible with the standard ATX 20-pin connector, despite a superficially similar form factor. The Gigabit Ethernet and Digital Audio G4 models use a 22-pin variant that adds a +28V trickle rail (pin 22) to supply standby power to the PCI slots and the Apple Display Connector (ADC) port whenever the machine is plugged in, even with the system switched off. The earlier AGP and PCI Graphics G4 models share the same 20-pin connector and pinout as the Power Mac G3 Blue and White. The QuickSilver and QuickSilver 2002 models use a further revised 22-pin variant with a +25V trickle rail and two ADC power lines, while the Mirrored Drive Doors (MDD) G4 uses a distinct 24-pin connector with an entirely different pinout.
| Pin | Signal | Color |
|---|---|---|
| 1 | +3.3V | Orange |
| 2 | +3.3V | Orange |
| 3 | GND | Black |
| 4 | +5V | Red |
| 5 | GND | Black |
| 6 | +5V | Red |
| 7 | GND | Black |
| 8 | +3.3V | Orange |
| 9 | NC | |
| 10 | 12V | Yellow |
| 11 | GND | Black |
| 12 | +3.3V | Orange |
| 13 | -12V | Blue |
| 14 | GND | Black |
| 15 | Power On | Green |
| 16 | GND | Black |
| 17 | GND | Black |
| 18 | GND | Black |
| 19 | GND | Black |
| 20 | +5V | Red |
| 21 | +5V | Red |
| 22 | +28V TRKI |
Signals
- +3.3V — 3.3-volt supply rail; present on pins 1, 2, 8, and 12.
- +5V — 5-volt supply rail; present on pins 4, 6, 20, and 21.
- 12V — 12-volt supply rail (pin 10).
- -12V — Negative 12-volt rail (pin 13).
- GND — Ground return; distributed across multiple pins for current capacity.
- Power On — Active-low signal (pin 15) used by the logic board to enable the power supply; equivalent in function to the ATX PS_ON signal but occupies a different pin position.
- NC — No connection on pin 9 for the Gigabit Ethernet and Digital Audio variants; the QuickSilver variant uses pin 9 for a second +25V ADC trickle line.
- +28V TRKI — 28-volt trickle (standby) output on pin 22; supplies the ADC display port and PCI slots with power whenever the machine is connected to mains, independently of the power switch state. This rail is specific to the Gigabit Ethernet and Digital Audio G4 models; the QuickSilver uses +25V instead.
Notes
- This connector is mechanically and electrically proprietary to Apple and must not be substituted with a standard ATX power supply.
- The pin labelled “+28V TRKI” in the table represents the trickle (TRKL) output; the trickle voltage differs across G4 sub-models (+28V on Gigabit Ethernet/Digital Audio, +25V on QuickSilver).
- The connector housing is keyed to prevent incorrect insertion; however, the 20-pin connector used on the earlier AGP/PCI Graphics G4 will seat partially into the 22-pin socket — always verify the model before connecting.
- The MDD (Mirrored Drive Doors) G4 uses a 24-pin power connector with a completely different pinout and is not covered by this page.
References
- Apple PowerMac G4 Service Source Manual (Apple Service Source K)
- Apple Knowledge Base: Power Mac G4 (Gigabit Ethernet): Power Supply Voltage Test (Apple Computer, Inc.)