Some ATX power supplies provide another 12V rail on the 4-pin molex connector for the CPU power: This is the pinout for the 24-pin and 20-pin ATX power supply connectors: Also take care to verify all voltages and pinout before making any changes, as your Mac SE could have been modified or the color codes could have faded over time. rated at -0.3A instead of -0.5A), since this voltage is rarely used by modern motherboards. Check the voltage ratings of your ATX power supply carefully, using this as a guide, prior to using it for your Mac SE. The ratings of the different rails should be printed clearly on the power supply. Mine reads +5V 6A, 1.25A, +12V 2.1A, -12V 0.5A.įinding a modern ATX power supply which satisfies the above ratings should be a breeze. One word of warning is that some compact power supplies may not provide enough current on the -12V rail (e.g. The reason for the independent rail is to avoid electromagnetic interference on the CRT circuits which may cause problems reading/writing to the drives. The connector also provides two independent 12V rails, via pin 5 (yellow) which is for the disk drives, and via pin 10 (red), labelled as 12V SWEEP, for the CRT circuitry. Just for reference, 5V (orange) is used for most of the logic chips while -12V (green) is for the audio and serial ports. The color-coded 10-pin power connector is described below:

The first part is to find the pinout of the Macintosh SE power supply, which is available from here. Not bothering to repair the antique power supply, I decided to replace it with a modern ATX power supply, perhaps with some modding of the connectors.

The most likely culprit was the RIFA line filter capacitors well known for causing these kinds of dramatic failures. I quickly pulled the power cord and waited a few minutes before I disassembled the machine, locating the faulty power supply unit: I was using my vintage Macintosh SE when it finally died – there was a loud bang followed by columns of smoke, and the screen turned off.

Mac mini power supply pinout