When the "revival" of the computer with processor AMD ATHLON K7-600 and the motherboard GIGABYTE GA-7IXE author unpleasantly surprised by the strong heating of the oxide capacitors and chokes mains filter CPU - temperature clearly exceeded the acceptable value. But the Board was new, under warranty, and this fact had to accept. During subsequent periodic inspections obviously overheated capacitors and chokes reminded that this issue should be ACE to understand. But, as often happens in life, to complete this work lacked "trigger pulse". They became, as the author writes, article A. Sorokin "Peculiarities of use of capacitors and power supply circuits microprocessors", published in "Radio", 2003, № 1.
It is known that aluminum oxide capacitors have a large private inductance is proportional to their capacity, and can operate normally high frequencies (HF). Therefore, in circuits with broadband signal parallel to them be sure to install practically non-inductive ceramic capacitors. Exactly made filters in the power supply circuits of radios and televisions, and for all it's long been a truism.
Here are some specific data of the power supply circuits of the processor Board, on which refinement was carried out. This information will not only help the reader better understand the changes, but also will serve as a guide when conducting similar work on the motherboards of other types.
The filter processor supply voltage of 1.6 V is composed of five included for capacitors in parallel 1200 µf x 6.3 In and two connected also in parallel, inductors, and voltage of 5 In - of four capacitors and one throttle. On Board are installed ceramic capacitors for surface mount, shunt oxide, but they seem to have been ineffective.
The objective of the first phase of work was "unloading" of capacitors from the RF component. The best option would be to install ceramic capacitor directly on the PCB on which is mounted a microprocessor, but it slowing down and there was the danger of damage. So I had remain somewhat less effective - mounting Leadless capacitors on the findings of the oxide. It was set six capacitors the capacitance of 2.2 µf with a rated voltage of 16 V, four in the food chain and 1.6 In two - circuit power supply of 5 V. Since the distance between the conclusions of the oxide the capacitor is greater than the length of the ceramic, one end of the latter primavalle directly to the output of the oxide, and the other through the insertion of bent cut in half tinned wire diameter 0,5...0,6 mm.
Once finalized, the heating of capacitors has decreased considerably, and added a little later three more Leadless capacitor (one for each of the remaining oxide) hardly changed the picture.
The next challenge is reducing heating chokes. In the power supply circuit 1.6 V they had three turns of enameled wire with a diameter of 1.7 mm, wound on a ring core with an outside diameter of 12.7 mm, and in the power supply circuit 5 In five turns wire diameter of 1.4 mm on the same core. The core material unknown, but it can be assumed that the ferrite.
Causes heating of the reactors is well known. It is the allocation of power to active the resistance wire winding (Joule heat) and the so-called surface the effect that causes the increase of this resistance for high frequency components.
Because the active resistance of the winding is within fractions of an Ohm (measure it conventional devices cannot), the influence of the first component is small in the first approximation it can be neglected. Greatest "contribution" makes the second component. In addition, due to the saturation of the core high current inductance of the inductor is not sufficient for good filtration of the variable component.
The simplest revision of the throttle - introducing gap in the core. For this purpose the throttle fed from the circuit Board and a diamond saw, make a cut with a width of about 1 mm in the place where it touches the wire. The inductance of the inductor with several decreases, but it is easy to recover by increasing the number of turns.
To reduce the influence of the surface effect is more complicated because it requires replacement wire winding the cable with the same cross-sectional area made of more thin wires. They are thinner, the less effect surface effect, less than the diameter of the wiring (due to the higher fill factor) and, in addition, it becomes softer and easier to wrap. However, a large number of wires complicates the manufacture of the harness, wire sew-2 of 0.35. For winding choke in the power supply circuit +5 V applied to the harness of wires 16 to a length of 180 mm, and chokes in the power supply circuit of the nucleus - 25 wire length 160 mm.
Manufacture of wiring is simple, although very time consuming. Initially, one of the ends each wire is freed from the insulation to a length of 5...8 mm and obluzhivayut, then put the tinned wire ends together and aligning the ends, twist in harness. Because its diameter is in any case greater than the diameter of replaced the wires, cut the last (pre-stripped and tinned) insert into the end of the harness, the connection is wrapped with a thin tinned wire and carefully probailout. Then the harness is wound on the core with a pre - made the incision. To compensate for the reduction of inductance due to the introduction of gap number of turns increase, respectively, to 9 and 5. After winding the second the end of the harness to shorten to the desired length and prepare for installation similarly to that described above.
New chokes cannot be installed flush to the Board as stood nepridumannye, but it's even better because the appeared gap improves cooling Board and the chokes. The result is a double effect - reduce the temperature of the reactors and improving their cooling.
Check the modified power supply filters showed the following. After turning on computer and loading the operating system the heating of the capacitors and chokes hardly palpable. At the big loading of the processor (a complex task) heating chokes becomes noticeable, but it is much less than before the rework.
Finally - a few tips for those who, after reading this article, think about improving the reliability of your computer. First of all, you need find out the real need for the described improvements. In modern processors, for example, ATHLON 1700, ceramic decoupling capacitors are mounted directly on the Board which includes a microprocessor. In addition, due to the large computing power in many cases (for example, if you set text editor Word processor actually "resting", so he the mains filter elements heat up a little. Heating may increase substantially when loading of the processor complex mathematical tasks (by the way, to them are and games like 3D"shooter"). And if in this mode the computer used for a long time, it makes sense to finalize it. Oxide capacitors in any case it is advisable to shunt the ceramic. In the chokes to try be limited to the notch of the core, and if this be insufficient, replace single wire harness.
Author: Grishin, Moscow