ATX Power Supply modification

The simple ATX power supply is a PC standard. However some OEMs will use different pinouts for the voltage/signal rails and once in a blue moon use a different rear panel layout like putting the exhaust fan in the middle or putting the IEC power socket on the left or right side. Typically it’s doesn’t matter but rarely it does.

The HP server I recently got had a bad power supply. A replacement runs about a hundred bucks. I have plenty of extra supplies however the odd case design uses a bezel to hold the power supply. The bezel is fitted for the power supply’s layout.


The power supply I want to use looks like this.


I have two options to do this. I could get some sheet metal and cut it out and create a new bezel, Or I could transplant the guts from the supply I want to use and reuse the chassis from the old power supply. Since I don’t have the proper tools at the moment I have to transplant. I’ve done this many times before. Sometimes the circuit board uses the same mount points and sometimes it doesn’t but there is a simple fix if I run into that. The original power supply automatically detects 120/220 50/60hz so there is no switch. I’m not planning to move out of the country anytime soon so I’ll bypass the selection switch. I will also need to bypass the mains power switch as well. I can reuse the IEC and fan from the old supply. If by chance the mount points for the circuit board doesn’t match up I can bend the old mount points away and use some machine screws and nuts to mount the board. I think I might have some standoffs somewhere in my junk box.

Now transplanting power supplies isn’t the easiest. Safety is key when doing something like this. The power supply is earth referenced ground for safety reasons. You can turn it into a floating supply but you’ll increase the chances of the computer hardware getting damaged from static, power outage or brownouts. Typically one or two of the screw mount points is connected to the earth ground. Another thing to keep in mind is in some power supplies the switching mosfets that are connected to the heat sink on the circuit board are at voltage potential so make sure the heat sink/s does not touch the chassis. If you have no other choice then use some heat resistant rubber, plastic or ceramic and use it as a barrier between the heat sink and chassis. Last thing you want is to create a short and blow up the supply or even worse the whole computer. Do not and I repeat DO NOT turn on the supply with out it’s chassis. It’s a good chance to get zapped with 120 or higher voltages depending what country or power applications are used.

A few things you can do also when doing a transplant you can get rid or add more molex connectors for devices. Honestly when I build a new system I attend to crack open the power supply and remove unwanted items such as the mini molex connector that is typically used for floppy drives. Also these days since everything is SATA I will remove the older molex style connectors. Maybe I’ll leave one for just in case depending on if I plan to add extra fans or lighting. Sometimes I’ll run into a cheap power supply that doesn’t have the 3.3v rail for the SATA drives and a few times while I had it open I would run a primary 16 gauge wire from the 3.3v rail and attach it to the SATA power connectors if possible. I myself attend to buy cheap power supplies. Honestly I never had any issues with the cheap ones. Now I’ve had issues with OEM supplies that come with a system. I’ve only been able to buy a modular supply once. I’m too old school to deal with the modular stuff.


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