Computer motherboard failure No boot what's going on

Computer motherboard failure to boot solution:

The motherboard's power-on circuit control way, has through the South Bridge direct control, has through the I/O direct control, also has through the gate circuit control. Regardless of the Power-on circuit control mode, they are the same principle, that is, through the Power-on key to control the ATX power output, so that the motherboard to the electrical work.

ATX Power supply on standby 9 feet have 5V voltage, this voltage is for the power-on circuit to provide standby voltage. 14 feet for the control foot, high level (3.6V or above) when the ATX power supply for standby, low electricity peacetime for the working state. The rest of the pins have no voltage output when they are on standby.

When we press the POWER switch (pw-on), also triggered the motherboard boot circuit, the start-up circuit in the South Bridge chip or I/O chip on the trigger signal processing, the final issue of control signal, the ATX power supply of the 14th needle (24-pin power supply plug to 16-pin) high potential pull low, ATX power supply this foot into a low level, Will output a variety of voltages for the motherboard power supply.

Although in the motherboard parts of the circuit design and application of components and chip combination layout is not exactly the same, but the principle and purpose of implementation is always consistent, that is, through the control of the Pson pins to control ATX power supply and shutdown, and then control the motherboard on and off. When the Pson pin voltage is high, the main power supply circuit in the ATX power supply is turned off; when the voltage of the Pson pins becomes low, the main power circuit in the ATX power supply is started, thus outputting various voltages. Therefore, control the voltage of the Pson pins, also control the motherboard open and close.

Power-on signal triggering process: pwr→ gate circuit → South Bridge (or I/O) → Gate circuit (or transistor) →ps on (Green Line)

Here we want to introduce the "power sequencing"-the concept of electric timing, the motherboard for the requirements of the power is very strict, all kinds of necessary conditions must have a sequential order, which is what we call the power sequencing, A condition can be transferred to the next step, if one of the links occurred in the fault, the whole process can not continue, of course, can not make the motherboard on the electricity. The most basic power sequencing on the motherboard can be understood as such a process:

RTCRST#→VSB Standby Voltage →rtcrst#→slp_s3#→pson#

Mastering the Power sequencing process, we can take a step-by-step check, find the failure of the normal implementation of the step, and to exclude. The detailed process of the entire power sequencing is described below:

1, before the ATX power supply, the battery on the motherboard generated vbat voltage through the CMOS jumper on the rtcrst# to supply the South Bridge, rctrst# used to reset the logic circuit inside the South Bridge, so we should first measure whether the battery has electricity, CMOS jumper on whether there is a 2.5v-3v voltage.

2, check whether the crystal output of the frequency of 32.768KHz to the South Bridge (in the NForce chipset motherboard, but also to measure the 25MHz crystal oscillator whether the vibration)

3, plug in the ATX power supply, check the 5VSB, 3VSB, 1.8VSB, 1.5VSB, 1.2VSB waiting for the machine voltage is normal conversion (5VSB and 3VSB standby voltage is required on each motherboard, the other standby voltage is based on the motherboard chipset different and different, Please refer to the datasheet of the related chipset in detail)

4, check the rsmrst# signal is 3.3V high level, rsmrst# signal is used to inform the South Bridge 5VSB and 3VSB standby voltage normal signal, if this signal is low, the South Bridge received the wrong information, that the corresponding standby voltage is not OK, so will not carry out the next step on the electric action. rsmrst# can be measured in I/O, integrated network card and other components, in addition to measuring the voltage of the rsmrst# signal, but also to measure the rsmrst# signal to the ground resistance, if the rsmrst# signal in the short circuit state is not good, the actual maintenance, many of the fault is i/ O or bad card caused rmsrst# signal is not normal.

5, check whether the South Bridge issued a SUSCLK this 32.768KHz frequency.

6. Short connect the motherboard power switch, sends out a pwbtn# signal to I/O,I/O receives this signal, after the internal logic processing sends out a pwbtin# to the South Bridge.

7. The South Bridge received pwbtin# signal, issued slp_s3# to I/O,I/O received this signal after the internal logic processing issued a pson# signal to ATX power supply, ATX power to the low level of the pson# signal, began to work, issued each basic voltage to the motherboard on the various components, Complete the electrical process. Note: The above for the Intel chipset's power flow, via and SIS of the electrical process is somewhat different, which removed the I/O part, that is, trigger the motherboard power switch, directly sent out pwbtn# to the South Bridge, South Bridge turned out susb# (ie slp_s3#) signal to a transistor B pole, The transistor's C-polar Pson pin is connected to the ATX power supply, E Pole connect gnd,susb# for high level, this transistor C, e pole conduction, will pson# pull low, complete the electrical process (some motherboards are using MOS tube, but its principle is the same, that is, here with susb# control Pson grounding, In the form of switch tube to complete the electricity)

First step: Pre-overhaul preparation

First troubleshoot the primary power supply. Connect the power, press the boot key to boot. If no power is available, disconnect the rear cover of the chassis, unplug the ATX power cord, and use tweezers to short green and black lines. If the power supply fan turns at this point, the power supply is good. If not, replace the power supply. Before replacing the power supply remember to measure the ATX interface on the motherboard on the ground resistance is normal, there is no short-circuit phenomenon, so as not to burn new power.

Then troubleshoot the chassis panel. If the power supply is good, the ATX power cord is plugged into the motherboard, the motherboard to find the switch needle and then dial out, with a screwdriver short switch needle trigger power switch, see whether the boot, if you can, it is the main engine box switch is bad, the main box switch to remove the cleaning. If the short-circuit switch pin triggers the power supply or does not boot, indicating the failure on the motherboard.

Check the appearance. Determine the failure of the motherboard, check the main components on the motherboard has no burn marks, electrolytic capacitors have no drum. Focus on the north-South Bridge, I/O, power supply mos tube. If a significant burn is found, the first part of the burn must be replaced.

Sometimes we need to remove the motherboard from the chassis and clean the dust off the board so as not to hinder maintenance. Mainly observe the edge of the motherboard and the back, such as PCB edge disconnection, knock angle, drop parts and other man-made failures, the first to make up the line, fill the work. And the South Bridge's surface color is darker, a slight burn mark may not be easy to observe, we can tilt the board to a certain angle, to the daylight or light to view. To see if there is burns at the same time, but also the main board on whether there is a pungent odor, which is also a common method of appearance inspection.

Step two: Impose power on the motherboard

When the motherboard does not power, first by imposing electrical method to locate the motherboard does not power the specific fault circuit. That is, a direct short circuit to connect the green and black lines. If at this time can be powered on, indicating the fault in the soft boot circuit itself. Then we use hand to touch I/O chip, South Bridge chip, some boot door circuit. Suspicion is the door circuit can be touched (door circuit is generally 8 feet). If a chip is hot, usually this chip is broken, direct replacement. In the Power-on circuit, the chip bad ratio is still very high.

If you can not add electricity at this time, indicating a serious short-circuit phenomenon. ATX Power supply internal protection, it does not allow itself to output voltage to the ground, so the power supply is automatically protected.

There may be short circuit, yellow line short circuit, Purple Line short circuit or the main power supply side of the CPU short-circuit. The above short-circuit phenomenon, in the actual motherboard failure occurred in any one will appear forced to add electricity and not power.

For the red line short circuit may be the main board of a field effect tube short-circuit or Power Manager short circuit, there is a door circuit short-circuit or I/O short-circuit, as well as a bridge short-circuit, there may be a 5V filter capacitor short-circuit. Measure the 5V ATX value or power supply tube to the ground number of the eulogy owed 穸 margin Fontanel, u5 mu margin jue  stool about 380 ohms, then you are obviously measuring the power supply tube to the ground 0 ohms or nearly 0 ohms, this time must be said that the motherboard chip to the ground short-circuit phenomenon caused by ATX protection.

For Yellow Line 12V short circuit is usually the power management itself and 12V filter capacitor short-circuit, for 12V short-circuit also may be a serial chip problem. For the Purple Line short circuit may be the South Bridge, I/O, Fet and gate circuits, as well as the Purple Line filter capacitor and violet line voltage regulator diode caused.

For the CPU main power supply short-circuit may be FET, Power Manager and main power filter capacitor. For P4 motherboard, the CPU main power supply short circuit may also be the North bridge short circuit. Detect the ATX power cord to the ground short circuit, and then run the circuit along the line to find the relevant damaged components, replaced.

Step three: Measure the power supply to ground resistance of each road

If the above imposition of electricity, the CPU fan can be normal rotation, you can determine the power circuit is basically normal, this step can be skipped. If the CPU fan does not turn or turn to stop, most likely the motherboard has a short circuit.

Note: Intel's motherboard does not turn on the CPU without the boot, the fake load is useless. Some motherboards that use 82801db+8712/8702 I/O, such as: GA motherboard has no CPU without the phenomenon of boot. Performance, each point PWR can power 1-2 seconds, then power off, and then point PWR can also trigger (such as the point can not be triggered is the power overload caused by protection, which is to distinguish between power circuit problems or other boot circuit problems such as a method). Another: 82801DB, EB's South bridge, forcibly boot or abnormal shutdown, there is the phenomenon of intense hair hot.

When using a multimeter to measure whether there is a short-circuit, first disconnect the power supply, dial out the ATX power cord. Then the multimeter to the diode position, Red pen grounding, black table pen to test points, we call it the measurement of the ground resistance.

1. Measure the 3.3V on the ATX power supply, 5V, 5VSB, 12V voltage whether there is a short circuit phenomenon, usually, its resistance to the earth should be more than 100, if there is a phenomenon under 100, it may be in a short circuit state (the new motherboard, 3.3V voltage to the normal value of the ground may be around 100, So the 100 value can only be used as a reference number, not an accurate indicator, the best way is to find a piece of the same motherboard for comparison measurement. If there is a short circuit, the specific voltage of short-circuit according to the replacement method to eliminate short-circuit fault.

2. Measuring 4PIN Small ATX plug on the 12V power port on the ground is short (this 12V and large ATX 12V on the line voltage, can not be confused, this 12V voltage is mainly for the CPU to provide work voltage), if the 12V voltage has short-circuit phenomenon, To measure the CPU's PWM power supply part of the MOS tube, to see if there is a breakdown of the phenomenon, in the actual maintenance, most of the upper tube breakdown, we can first measure each phase of the power supply of the upper tube g, s polar, D, s polar resistance to judge is that phase of the tube is broken down, and to be replaced, at the same time need to note that, In conditions permitting, it is best to replace all the upper and lower tubes of the whole phase, and also to replace the drive chips.

3. Measurement of the motherboard on each of the power supply conversion of the MOS tube has a short phenomenon, such as memory voltage VCC_DDR, AGP voltage VDDQ, and in accordance with this to determine whether the north-south Bridge has short circuit situation.

4. Measuring the motherboard 3VSB, 1.5VSB, 1.2VSB waiting for the machine voltage is short, the most common is the 3VSB voltage short-circuit, if found this situation, first of all to determine whether the network card is damaged, you can measure the interface of the network card caused by the ground resistance to judge, If the value of the polar body on the interface of the NIC is normal, remove the NIC first and then measure whether the 3VSB is normal or not. In addition to the network card short circuit, the most likely cause 3VSB short-circuit is the South Bridge.

5. If the value of the ground survey found 3.3V short-circuit (refers to a direct short circuit, the value of 0) to exclude the 3.3V short-circuit method is also forced to add electricity, because according to experience 3.3V short circuit is likely to be caused by North Bridge, South Bridge. So first to feel the North Bridge, South Bridge temperature (North Bridge because of the heat sink, it is best to touch its back), the possibility of excluding its short circuit, followed by the clock, integrated sound card, network card and so on.

6. On the motherboard the most likely to cause short-circuit in the main power supply part: Q1, Power IC. After a short circuit, should first Test Q1 whether the breakdown. On Intel chipset motherboards, the 3.3V and 5V short-circuit at the same time, most of the South bridge is bad.