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PC Power Supply Knowledge

PC into the system, each component has a single source of power - is the power supply. Power supply must be uninterrupted for all the equipment to provide a stable, continuous current. If the excess or shortage of power supply, the connected device may not function properly, looks like the same as bad. For example, the memory can not be refreshed, resulting in data loss will lead to software errors; the CPU may be deadlock, or randomly re-start; hard disk may not turn, can not be normal processing control signals. Since so many devices and power are closely related, then the power supply as a PC system, the most important components is anything but over. Looking at statistics from the computer failures, power failures part of the total failure rate is very high percentage.

(A) power supply problems, its performance is multifaceted:
1, leading to hard disk bad sectors or damaged. Easily lead to poor power supply false bad sectors hard disk, this failure may generally be repaired by software. If you encounter such a situation, we should first check the power supply. In repairing the hard drive should also be for a good power supply.
2, noise increases. Not only the power supply itself, the fan noise will increase, but also may lead to increased noise sound card.
3, CD-ROM drive access performance poor. If your new computer or new purchase with a CD-ROM to read the disk properly, is likely to be power supply problem.
4, overclocking instability. Overclocking stability and power quality is good or bad A great deal.
5, the display on the water ripple. May be the power of electromagnetic radiation diarrhea, interfere too much.
6, the host often baffling to restart. The power supply may be inadequate.
7, bad power supply on the +5 VSB not provide 10mA of current, resulting in sleep after a long Shuibu Xing, and +5 V instability will lead to frequent breakdown of the mouse.
(B) the maintenance of several cases of power supply
Compared with the computer's other components, power supply part of the discrete components used in the largest share, which also provides for the maintenance of a more suitable opportunity to repair it yourself. As long as familiar with the PWM switching DC power supply of the basic principle of no work in the schematic diagram of the case, according to basically be able to understand the physical working principle of the power supply and devices working state, it is easy to start with maintenance.
Computer power supply in general susceptible to failure are the following: fuse fuse, power output or no output voltage instability, power output, but there is no boot display, power load capacity poor. The following describes each of its repair methods:
Fault 1: fuse fuse
Recurrence of such a failure, first open the power supply case, check the power supply fuse is blown, whereby the inverter circuit can be initially determined whether there has been a failure. If so, is not outside the following three conditions: the results of input circuit is a bridge rectifier diode breakdown; high-pressure filter electrolytic capacitor breakdown; inverter power switch is damaged. The main reason is because the DC filtering and conversion oscillator circuit to work long hours in high-voltage (+300 V), high current state, especially because of changes in a larger AC voltage, output load is heavy, the easy to fuse fuse failure occurs. DC filter circuit consists of four rectifier diodes, two current-limiting resistor of about 100KΩ, and about two 330μF electrolytic capacitor component; conversion oscillator circuit is primarily installed in the same heat sink on the two models the same high-power switch tube.
After the exchange of fuse fuse, unplug the power plug off, first of all the circuit board carefully observed the appearance of the high-voltage components, whether they have been burnt or electrolyte overflow puncture marks, without exception, with the multimeter measure the value of the input, if less than the 200KΩ, shows the back-end there is the phenomenon of partial short-circuit, and then were measured two high-power switch tube e, c resistance among most, if less than 100KΩ, is illustrated switch has been damaged, measuring four diode rectifier positive and negative to the resistors and two current-limiting resistance is used multimeter to measure the charge and discharge conditions in order to determine whether it is normal. Also in the replacement switch, if you can not find the same models to choose alternative products, we should pay attention to the collector - emitter reverse breakdown voltage Vceo, the maximum allowable collector power dissipation Pcm, the collector - base hit reverse wear the parameters Vcbo voltage should be greater than or equal to the original transistor parameters. Then one should pay attention to is this: must not discover the damage of a component, the replacement after a direct boot, this is likely due to other high-voltage components, there are still failures in turn replace the damaged components. Must be all of the above-mentioned high-voltage components, the circuit to conduct a comprehensive inspection measurement, fuse fuse failure can be completely ruled out.
Fault 2: No DC voltage output or voltage output instability
Troubleshooting: If the fuse intact, there is load conditions, the levels of DC voltage without output, its possible causes are: the power appears open, short-circuit phenomenon, over-voltage, over-current protection circuit failure, oscillation circuit not working, Power overload, high-frequency rectifier diode rectifier filter circuit is breakdown, filter capacitor leakage, etc.. Approach as follows: using multimeter measuring system board +5 V power supply to ground resistance, if it is greater than 0.8Ω, is illustrated in the system board without short-circuit phenomenon; will be changed to minimize the computer configuration, namely the machine, leaving only the motherboard, power supply, buzzer , measuring the output DC voltage, if still no output, indicating fault lies in the microcomputer power supply control circuit. Mainly by the control circuitry integrated switching power supply controller (TL-496, GS3424, etc.) and over-voltage protection circuit, the control circuit is working properly is directly related to whether the output DC voltage. Over-voltage protection circuit mainly by small-power transistor, or silicon and related components, can be used whether the multimeter measuring the transistor is the breakdown (if the SCR welding Zexu measured), the related resistors and capacitors for damage. At last, multimeter static measurements of high-frequency filter circuit in the rectifier diodes and low-voltage filter capacitor is damaged.

2 PC Power Xiangjie
Fault 3: power supply output, but the boot no display
Troubleshooting: When this failure may be due to "POWER GOOD" input Reset signal delay time is not enough, or "POWER GOOD" no output.
After boot, with Voltage Meter "POWERGOOD" The output (then host of a pin power plug), if there is no +5 V output, and then check the time delay components, if +5 V output, then the replacement of the delay capacitor delay circuit that is be.
Fault 4: The power load capacity of poor
Troubleshooting: power supply only to the motherboard, floppy drive to work normally when powered, when connected to the hard disk, CD-ROM, the white screen was not working properly. Its possible causes are: the transistor operating point did not select a good, high-voltage filter capacitor leakage or damage, regulator diode heat leakage, damage, etc. rectifier diode.
Exchange oscillation circuit each transistor, so that the gain increase, or transfer large transistor operating point. A problem with the multimeter to detect the components, the replacement of SCR, voltage regulator diode, high voltage filter capacitor or rectifier diode can be.
Fault 5: No DC output
Parts which may occur include: insurance, tube blown, converter does not work, the control circuit fault. Open the power box and found that fuse removed. According to the user to reflect repeated for repeated burning fuse. Under welding rectifier diode and converter power switch tube, with the multimeter test are normal, with high impedance input file detected no short-circuit phenomenon of exchange. Detection of the normal rectifier filter capacitor. Blowing under the insurance policy governing the phenomenon of judging, fault location should be the primary winding of the converter before, but found no short-circuit place. Had no choice but to restore the original state, for insurance, power-tube experiments. Connected to AC power, insurance blown, immediately disconnect the AC power check fuse burned black. AC input circuit can be seen with severe short-circuit phenomenon, disconnect the AC input rectifier bridge. In the rectified AC input at both ends of the bridge increases then the insurance control, directly on the receipt of AC power. Connected to power supply, regulated power supply fan rotation to normal, testing the DC output voltage to normal. Fault location can be seen in AC filter circuit, while with the multimeter test has not. Then think of an alternative method, removed the power supply from another exchange of two filter capacitor replacement (due to welding simple, first-for-capacitor) plus electrical test, DC regulated power supply is working correctly. Fault can be seen in these two capacitors in the area, using high-voltage insulation testing instrument, in which a high voltage capacitor breakdown.
Fault 6: After booting the computer self-test, guide to normal, the screen prompts "INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY" when you insert a DOS disk, floppy drive does not read the disk.
Analysis from the fault, fault located in the floppy disk drive, floppy disk adapter or system. After substitution to prove that this machine on a floppy disk adapter, floppy disk drive is good. Finally removed the motherboard to verify that is good, and to restore the original state after power-up test, failure can not be eliminated. It was suspected that the power supply section.
In the 5-inch floppy drive enclosure unplug the power plug. Boot, with multimeter test DC output, +5 V, +12 V are normal. Power plugged in floppy drive power plugs, and then start the same fault. Measured after full load DC output +5 V for +4.1 V, +2 V to +10.4 V. As the power supply output voltage to reduce the impact the normal operation of floppy drive motor, resulting in not properly read the disk. Reason to find later, removed the power supply for maintenance, when the load lighter, the power output normal; when the load increased, the power output reduced. Description regulated power supply to reduce load capacity. Power on the lid, using the oscilloscope test TL494 component 8,11-side and signal amplification tube wave amplitude independent of the load effect. +5 V winding converter detected waveform, the load of its influence, but the magnitude of changes is very small, and it is suspected +5 V rectifier diode forward voltage drop become larger, resulting in reduced output capability. +5 V rectifier replaced again after power-up test, fault can not be excluded, when the maintenance into a corner. Later, calm analysis of the factors that also affect the DC output power switch. Replacement power switch tube boot test, load change, the DC output normal troubleshooting. Replaced the power tubes JL-1 test, a small magnification. After the Department learned that Taiwan from the user's machine has been working continuously for four more years. This is a power transistor aging caused the failure. Examples drawn from this date, computer failure should first check the DC power supply output voltage, which is the maintenance personnel to narrow the scope of failure, rapid troubleshooting extremely useful.
Fault 7: PC, power supply, one Taiwan, plus full load after the +5 V output +3.5 V, +12 V output +9 V a little more. Potentiometer to adjust +5 V sample, the voltage can not raise.
According to the phenomenon of fault analysis, power supply after power DC output, indicating the power is basically able to work properly. Potentiometer to adjust +5 V sample, the voltage does not increase, indicating failure occurred in the control circuit. In the power supply +3.5 V power output after the analysis of the work may be a result of unilateral control signal.
According to failure analysis, power supply, after testing with the multimeter TL494 each foot level, due to DC output is not normal, so one side than the normal low level. 8,11 level at both ends of stalls measuring DC voltage is normal at around 2.0V. 8,11 observed with an oscilloscope and signal amplification tube at both ends of the output in the range of about 12V are normal, ruled out the suspicion of unilateral work. In the fault location can not be ascertained cases, with the new TL494 circuit voltage can be replaced after the +5 V to +4 V a little more, still can not reach the normal output. The final decision for power switch, changing to normal after the DC output, troubleshooting. From the maintenance of analysis, it is also due to switch from failures caused by aging.
Fault eight: PC machine one, connected to the power switch, power indicator light does not shine, computer can not be started. Continuously press the power switch several times, and sometimes by chance may be to start one, start after the computer is functioning correctly. Shutdown and then start, then there could not be activated phenomenon.
According to analysis of failure phenomena may be caused by poor contact power switch. For the power switch, the fault can not be excluded. But in turn the power switch, so that about ten minutes later, the computer automatically activated, thus analysis, fault lies in the power control part of the temperature of the components caused by failure of performance of non-performing.
The power supply from the chassis and remove, open the power supply cover, coupled with the load power detection, +5 V at boot time there are +1.2 V, +12 V output of a +3 V, AC 300V output of the normal rectifier. Cha-power switch is good, with a hot iron after the start of the heating power tube, fault can not be excluded, thereby excluding the poor performance of power transistor temperature suspects to determine fault located in the converter circuit part of the secondary winding back. After power-up boot with a multimeter measuring the electrical TL494 usually found in the foot, auxiliary power supply input voltage is only a little more than 5V, power-on time, voltage and gradually rise in the auxiliary supply voltage escalation process, the power output gradually increased to normal. This is like a capacitor charging process is slow. Therefore, auxiliary power supply circuit to find the capacitor C15, a larger leakage measured with a multimeter. After changing Troubleshooting.

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