The illustrations refer to the TrueControl 550 unit, which has all the three wires (the “best” case). I didn’t do mods for the +5v and +12v rails since the regular voltage ranges permitted setting them to +5.35v and +12.42v, which was enough for me. I found the maximum of +3.42v on the +3.3v rail rather insufficient, though. So, I will perform this mod as an example. Everything is going to be exactly the same with any other PSU.
I hope you are experienced enough for the following warning to be unnecessary, but anyway: before following any of the instructions below, detach the PSU from all the devices (mainboard, graphics card, drives and so on) as well as from the power source (by physically removing its plug from the wall outlet).
Let’s start by seeking out the sense wire. It’s simple. The necessary wires are at the sides of the ATX connector: the +3.3v orange wire on one side, and the red and yellow (+5v and +12v) wires on the other side. As you see, not only thick power wires come out of the ATX connector, but also thin wires of the same color. We need these thin wires. The thin orange wire is the sense wire for the +3.3v power rail.
You choose a location of the cut that’s convenient to you. I, personally, preferred making it inside the PSU case, outputting the resistor through the hole for the wires. I think this is the most esthetic and ergonomic design.
So, I disassemble the PSU and find the necessary wire in the heap (and make myself absolutely sure it is the correct wire!) Then I make a cut in it.
To do the mod, I need a 50Ohm fixed resistor and a 10,000Ohm variable resistor, desirably with many revolutions for a smoother control. The proposed scheme is not the only one. There are several other combinations of these elements possible, and some guides contain their combinations for 3.3v, 5v and 12v circuits. All these schemes do work. The advantage of my version is its universality (the same components for all the three circuits) and the maximum availability of the components – I use the most simple and widespread nominal values.
So, I solder a 50Ohm fixed resistor into the cut in the wire. Then, after this resistor, towards the PSU (not towards the ATX connector!), I hang one output of a 10,000Ohm variable resistor. The second output goes to the ground, which can be found in the PSU itself.
All the three modifications are performed identically (for +3.3v, +5v and +12v rails), only on different wires: you need to repeat the above-described steps for the red and yellow sense wires. If your PSU doesn’t have three independent sense wires, you’ll have to be content with one or two modifications.
Attention! I want to remind you that the resistance of the variable resistor must be initially set to the maximum, i.e. 10,000 Ohms. Make sure about that before taking up the soldering iron! After soldering, isolate carefully all the bared spots. Neglecting these requirements may leave you with a dead PSU and other hardware.