The computer can't be turned on is a problem that many friends have encountered. Generally, the computer can't be turned on related to the power supply and the motherboard boot circuit, but there are other problems. Today we say that the computer can't be turned on. Troubleshooting methods and steps: judge the computer power supply is good. Bad first connect the power supply, press the switch, if it can not be powered, then pull the power of the host, use the tweezers to short the green and black wires of the power supply, see if the power supply fan does not turn, if it turns, the power supply is good, fault On the host side. Determine whether the computer host switch is good or bad: connect the ATX power cable to the motherboard, pull up the switch pin and reset pin on the motherboard, and use the tweezers to short-circuit the switch pin to trigger the power switch to see if it can be turned on. If it can, it means The switch of the main chassis is broken, and the main box switch is removed and cleaned. If the short-circuit switch pin triggers the power or does not turn on, it means that the motherboard can't trigger the boot, remove the motherboard from the chassis for maintenance. Remove the motherboard and clean the dust on the board to prevent it from being repaired. First visually check to see if there are any components burned out on the main board, drum kits, and whether there are burnt or broken wires on the computer board. Put the motherboard in place, plug in the dummy load, plug in the power supply, test the card, and prepare for maintenance. When the main board is not powered, firstly, the specific fault circuit that the main board is not energized is located by the forced electric method. That is to say, the green line and the black line are directly shorted. If you can power up at this time, the fault is in the soft boot circuit itself. If power is not available at this time, there is a serious short circuit. ATX power supply internal protection, it does not allow the voltage output by itself to the ground, so the power supply is automatically protected inside. There may be a short circuit of the red line, a short circuit of the yellow line, a short circuit of the purple line or a short circuit of the main power supply terminal of the CPU. In the above short-circuit phenomenon, any one of the actual motherboard failures will be forced to be powered up and not powered. The reason for the red line short circuit may be a short circuit of the FET on the main board or a short circuit of the power manager, a short circuit of the gate circuit or an I/O short circuit, and a short circuit of the south bridge, or a short circuit of the 5V filter capacitor. Measure the value of the 5V ATX to ground or the value of the power supply pipe to the ground to see if it is shorted to ground. The normal value of the ground is about 380 ohms, then you obviously measure the power supply tube to ground 0 ohms or close to 0 ohms. At this time, it must be said that the motherboard has ATX protection caused by short circuit to ground. For the yellow line 12V short circuit is usually the power management itself and 12V filter capacitor short circuit, for the 12V short circuit may also be a problem with the serial port chip. The short circuit for the purple line may be caused by the south bridge, I/O, FET and gate circuit, as well as the purple line filter capacitor and the violet line Zener diode. The short circuit to the CPU mains supply may be the FET, the power manager and the main supply filter capacitor. For the P4 motherboard, the CPU main power supply short circuit may also be a short circuit of the North Bridge. Measure the ATX power line shorted to ground, and then run the circuit to find the relevant damaged components along the line to replace. If the power is applied forcibly, the fault is in the power-on fault. At this time, it is important to check the soft-start circuit itself and other circuits that are connected to the soft-start circuit. 1, COMS battery, some motherboards, battery power can not be turned on, but most of the motherboard does not have a battery does not affect the boot. Under normal circumstances, the COMS battery is a voltage of 2.6V or more, sometimes 2.6V & mdash; 3.3V voltage, this should also be noted. 2, COMS jumper, COMS jumper is not correct and can not be turned on, generally it is correct to jump on one or two, the third is grounded, if you jump on the second and third pins, you can not boot, pay attention. Some motherboard jumpers can be turned on after the jumper is wrong, because the real crystal power supply is provided by the purple line. 3. Measure whether the POWER switch pin has 3.3V or 5V voltage. The POWER switch pin is grounded. One pin is powered by purple 5V. The middle will pass some gates, resistors and other electronic components. If there is no 5V or 3.3 voltage to the switch pin. We look at the damage and replace it from the components of the ATX power supply purple 5V to the POWER. 4. Measure the crystal oscillator next to the South Bridge to see if it starts to vibrate. The starting voltage is about 0.5 and 1.6V. If not, replace the filter capacitor next to the crystal oscillator and the crystal itself. There is also a hand to touch, the two pins of the real crystal oscillator, the hand touch the motherboard can be powered, can work. However, after the real crystal is damaged, you can power up when you touch the real crystal, but the CPU does not work. At this time, I still continue to touch it by hand, so that the two pins of the real crystal oscillator are not in memory, and then the two pins of the real crystal oscillator are touched by hand, and the memory will pass. This is a typical phenomenon in which the peripheral circuit of a real-time crystal is damaged. This article comes from [System Home] www.xp85.com