The Effective Way on How to Use the Standard P4 ATX to Connect with 14pin Compaq PSU

You might find there are many cheap half-height Compaq desktops, such as EVO d500 SFF available on the market. Some people are deciding to replace the browsing pc downstairs with EVO d500 SFF, however it’s not as easy as you think, as when it comes to Compaq, it’s mostly a non-standard proprietary PSU.

Well, there is a solution for the above case, by replacing it with a 14pin connector. With this way, it can be used to convert a standard P4 ATX easily.

During the process, you have to pay attention to the Compaq mobo, as it takes 3.3V and 5V standby voltages, but the standard ATX PSUs offer only 5V. Hence, the missing 3.3V in the mobo won’t be able to turn the PSU on! For solving up the problem, the only option here is to add a voltage regulator on it. You might want to choose the LM317, as it’s much easier to deal with.

Last but not the least, you need to use an optocoupler to control switch between PSON at the PSU and ground, which is triggered by PSON at the mobo. Normally, both standby voltage LEDs on the mobo are going to light up, as soon as you connected power to the PSU!