P4 ATX to 14pin Compaq PSU Conversion

Some computer companies like to keep their customers buying replacement parts direct from them and not from the local computer shop. That is the case with lots of products from the Compaq line. In this case the Compaq had a proprietary power supply but with a bit of hacking a normal one was able to be used. If you are ever in the situation where you have a Compaq EVO d500 SFF computer with a blown power supply you can now refer to this hack and fix it on the cheap.

"The compaq mobo takes 3.3v and 5v standby voltages, but standard ATX psus offer only 5v. With the 3.3v missing the mobo won’t be able to turn the PSU on. There’s the option of hardwiring the PSON (perhaps to a switch, which would essentially be like an old AT psu functionality-wise, with the added trouble of having to switch the mobo on/off separately) , but that’s highly inconvenient and pretty lame 🙂 So the better solution is a voltage regulator. I chose the LM317 because I had one lying around and because it’s easy to deal with. It’s an adjustable reg, takes 2 resistors to adjust the output voltage, it’s relatively high power (which is completely unneeded here as the load on the 3.3v standby is minuscule) 1kOhm and 1.6kOhm adjustment resistors set the output voltage at 3.31volts, assuming a 5v input ( from the standard atx standby voltage pin ) There’s no drop whatsoever while in use, and the reg remains stone cold all the way, so the "heatsink" surface on my pcb is pretty pointless (I know it’s on the wrong side, but if it got hot it would be minimally useful regardless 🙂 ) also two caps for filtering were thrown in as suggested by the datasheet."