To the main question about mod a ordinary atx psu to obtain 24v, my answer is yes, it can be done. In a test, it delivered to me about 30v.
I made a couple of mods, one of them has an AT2005 and another has a SG6105, very different chips. The filosofy are very similar, but each chip has different qualities. SG6105 has protections over negative voltages, AT2005 hasn't. SG6105 has direct inputs on the real voltages under control (3.3v, 5v and 12v), AT2005 has inputs labeled v33, v5 and v12, but must be 2.5v on each to work. My first approach was to connect v33 (by a resistive divisor) and v5 inputs to +5vsb (+5V Stand By, obtained by a secondary/independent power supply inside the big one) and calculate a resistive divisor to the v12 input, connected to the new +24v output. The divisor can mantain the over/under voltage protection in a range, let's say, from +22v to +26v, more or less. In the SG6105 case, a potentiometer from pins 16/17 to ground makes the varaiability, in the AT2005 Vadj is the pin 2.
To obtain the maximum current the psu can deliver, I changed the output diodes (I really changed the entire rails from the transformer outputs). The diodes snubbers were maintained as original.
Remember to replace the output capacitors to more voltage ones, and a little tip: don't forget to change the load resistor of the psu. In my case, a 330 ohms/15w did the work.
I made a couple of mods, one of them has an AT2005 and another has a SG6105, very different chips. The filosofy are very similar, but each chip has different qualities. SG6105 has protections over negative voltages, AT2005 hasn't. SG6105 has direct inputs on the real voltages under control (3.3v, 5v and 12v), AT2005 has inputs labeled v33, v5 and v12, but must be 2.5v on each to work. My first approach was to connect v33 (by a resistive divisor) and v5 inputs to +5vsb (+5V Stand By, obtained by a secondary/independent power supply inside the big one) and calculate a resistive divisor to the v12 input, connected to the new +24v output. The divisor can mantain the over/under voltage protection in a range, let's say, from +22v to +26v, more or less. In the SG6105 case, a potentiometer from pins 16/17 to ground makes the varaiability, in the AT2005 Vadj is the pin 2.
To obtain the maximum current the psu can deliver, I changed the output diodes (I really changed the entire rails from the transformer outputs). The diodes snubbers were maintained as original.
Remember to replace the output capacitors to more voltage ones, and a little tip: don't forget to change the load resistor of the psu. In my case, a 330 ohms/15w did the work.
