Motherboard boot circuit repair steps

 

How the motherboard boot circuit works

After the motherboard key triggers the motherboard boot circuit, the boot circuit will trigger signal processing, and finally send a low-level signal to the power supply 14th feet, the power supply 14th feet of the High-level low, trigger the power supply, so that each pin of the power supply outputs the corresponding voltage, power supply for each device (that is, the power supply starts to work on the condition that the 14th feet of the power supply interface become low ).

Motherboard boot circuit detection steps

1. measure whether the Red 5 V and yellow 12 V of the ATX Power Supply interface are seriously short-circuited to the ground.

2. Is there a 2.5 V, 3.3 V, and 1.8 V standby voltage near the south bridge (the standby voltage varies depending on the south bridge)

3. Real-time crystal oscillator vibration (whether there is a voltage of about 0.4 V on both sides)

4. Whether the intermediate pin of the CMOS jumper is high. (Whether the CMOS settings are correct)

5. measure whether the POW switch has a height above 2.5 V.

6. The transient POW switch is used to determine whether a low-level South Bridge is successfully triggered (except for W83627HF)

7. Check whether the line from the Green Line to the south bridge is normal.

Note: easy-to-lose components in the boot circuit:

(1) door circuit and transistor related to the boot circuit.

(2) A forward voltage regulator or other power supply components that provide standby voltage to nanqiao.

(3) with I/O or South Bridge.

Motherboard boot circuit repair instance

1. GPS-810C (E) J, test point normal does not work, brush BIOS (with the joint crown 810 T) is invalid, after querying the North Bridge Power Supply of 3055 effect tube damage, board logo for Q4, after replacement OK.

2. -The P4 motherboard model is Titan667. The test card ranges from C1 to B0. If the test card passes through C1, it indicates that the CPU has been working and the memory is not enough. Check the memory power supply and find that the load voltage of the P4 motherboard is only 0.85 V. Normally, it should be 1.25 V. check whether it is connected to the Q96 and Q97 field tubes. after removal, the Q96 is measured as soft breakdown, and the fault is rectified after replacement.

3. -810 the motherboard cannot be lit. The test card is switched cyclically from D3 to 00 and from DE-00. This fault indicates that the memory cannot be detected, and the power supply, clock, reset, and chip selection of the memory are checked, line, column, select signal are normal, so the main board, the CPU and the fan are removed, found there is a scratch between the fan card and the main board, and has been divided into three lines, after completing the line, power-on measurement, everything is normal.

4. -The elite K7VMA motherboard has two CPU fan interfaces, one of which is automatically powered off. If an abnormal fan interface is found, the 5 V is supplied by the D4 diode, the diode is connected to the south bridge at the forward end. If the temperature control circuit in the south bridge is faulty, remove the diode and connect the fan's 5 V end to the D5 negative end.

5. Elite P6-IEAT or P6-IPAT, 815EP motherboard boot does not show, the normal voltage of the case for South Bridge bad. (Common Problem)

6. The AMD motherboard is automatically shut down after it enters the system. After the CPU fan is changed, the fault is solved.

7.-The Huatuo motherboard automatically enters the CMOS settings when it is started, and the dassic jumper is inserted with an error.

8. if the AGP video card is not on the p4asd motherboard, the PCI video card can work normally. If no video card is added, the VDDQ voltage is 3.3 V, and the 4× AGP video card is measured as 2.26 V, it should be 1.5 V if it is normal, so it is determined that there is a problem with the VDDQ power supply tube. After replacement, the fault will be solved.

9. k7TPRO motherboard, when detecting the video card, the code is too 26 don't light, check its VDDQ voltage is not normal, after the power supply tube replacement failure still, at this time, think of its control voltage output part, along the line, locate the 431 control and rectify the fault after the 431 change.

10. GA-8LD533, fault phenomenon, boot the test points are normal, CPU does not work, P4 test seat measurement, a large area of signal line is not bright, press the CPU seat, signal line is normal, so judge the virtual welding of the CPU seat, troubleshooting after welding.

11. MS-6153 motherboard, CPU does not work after boot, test the CPU operating voltage is not, Q1 control pole voltage is 0.45, Q2 control pole voltage is 1 V, after replacing the voltage IC, troubleshooting.

12. GA-8IE2004, fault to show the hard disk to detect the dead, sometimes can pass normally, but will crash, visual test memory near the power supply diode paste, with 5817 replacement, troubleshooting.

13. MS-6551, fault for plug CPU reset, PCI no reset, plug in the test card, reset light is always on, BIOS light and FRAME flashing, this board PCI, AGP and I/O for a reset signal, after I/O is removed, the reset is normal. Therefore, W83627HF I/O is damaged. After replacement, the fault is rectified.

14. the PCCHIPS MB815AT motherboard is faulty. After going 26, it will crash. The FRAME and BIOS lights on the test card will go off, and then click RESET. The RESET light will always be on, but it will not be able to be shut down. The fault is mostly due to BIOS program damage, however, the BIOS of the Board cannot be found. The I/O model of the ECS P6BAT motherboard is the same as that of the Board. After the board is flushed in, the fault will be rectified.

15. The Reset Voltage at the PCI unit is 875 V on the shuotek 0.45 main board. After checking the circuit, it is connected to the south bridge by 14 circuits. After replacement, the fault is rectified.

16. ASUS motherboard, P4266E 845 Chip Resistance, fault for PCI no reset, CPU no reset, first test North Bridge 2.5 V power supply is not normal, after replacing the memory part of the 4500 field tube, 2.5 V output is normal, there is still no reset on the CPU, after querying the south bridge 1.8 V operating voltage is only 1.25 V, this voltage is 1117 provided, change the regulator South Bridge 1.8 V normal, CPU reset is also normal, troubleshooting.