Replacing a Sun IPX Power Supply with a Mini ATX

The power supply is always the first thing to go on vintage Sun workstations. The original supplies in the SPARCstation IPC, IPX, and LX are proprietary units that are increasingly difficult to find and expensive when they do turn up. When the power supply in my SPARCstation IPX failed, I replaced it with a TF Skywindintl TF400, a compact 1U Mini ATX supply rated at 350 watts. It is inexpensive, readily available, and vastly overpowered for the IPX, which makes for a reliable replacement.

Why the TF400

The TF400 is a 1U form factor ATX supply, making it compact enough to fit in the IPX chassis alongside the motherboard. At 350 watts it provides far more current than the IPX requires, which means the supply runs cool and well within its limits. These units are available for around $30 to $40 and are commonly used in server and industrial applications, so they are reliable and easy to source.

The IPX motherboard requires only four voltages: +5V, +12V, -12V, and ground. The ATX standard provides all of these, so the conversion is straightforward wiring work.

IPX Motherboard Power Connector Pinout

The Sun IPC, IPX, and LX share the same motherboard power harness socket. The pinout is:

TF400 ATX Connector Pinout

The TF400 uses a standard modular ATX connector. The relevant outputs and their wire colors are:

Wiring the Conversion

The mapping between the ATX supply and the IPX motherboard connector is straightforward. The color coding between the two systems differs, so pay attention to the voltage labels rather than wire colors:

• +5V — ATX Red wires to IPX pins 1-4
• GND — ATX Black wires to IPX pins 5, 6, 8, 11
• +12V — ATX Yellow wires to IPX pins 7, 9. Note that on the ATX side these are yellow, but on the original IPX harness they were blue.
• -12V — ATX Light Blue wire to IPX pin 10. On the original IPX harness this was brown.
• POR — Pin 12 on the IPX connector is Power On Reset. I left this disconnected and it works fine.

Starting the Supply

ATX power supplies do not turn on by themselves. They require the PS_ON signal (the green wire on the ATX connector) to be shorted to ground. To make the supply start automatically when plugged in, connect the green PS_ON wire to any black ground wire. This causes the supply to power on as soon as AC power is applied, which replicates the behavior of the original IPX supply.

Physical Installation

The TF400’s 1U form factor is compact enough to mount in the area where the original IPX power supply sat. I mounted it to the original power supply bracket. The original IPX fans can be retained or replaced. The TF400 has its own internal fan as well.

The modular cable design of the TF400 is helpful here. Only the cables you need are connected to the supply, which reduces clutter in the already tight IPX chassis.

Applicability

This same approach works for the SPARCstation IPC and SPARCstation LX, as all three machines share the same motherboard power connector and voltage requirements. The wiring is identical across these models.

Parts List

The total cost is well under $60, compared to several hundred dollars for a working original Sun power supply if you can find one at all.