Working principle and maintenance method of motherboard reset circuit

Working principle and maintenance method of motherboard reset circuit

Working principle of reset circuit
　　　　　　　　 : RST is the reset button on the host case. The reset trigger circuit is integrated inside the south bridge. All reset trigger circuits are valid at low level. Compared with other voltages, the gray line is delayed by 100-500ms for output. It is at low level during the delay. To judge whether the reset is normal, you can measure whether there is a jump at each test point. The south bridge also needs a reset signal to work. (Some manufacturers have their own special power-on reset chip on their motherboards) 　　　Reset: 　　　　1. It refers to the process of providing an initialization signal to the device to restore the device to its original state. It is a basic condition for the motherboard to work. 　　　　2. Automatic reset is achieved by triggering the south bridge with a low level during the gray line delay period. After the south bridge works, it sends a reset signal to provide basic working conditions for each device. 　　　　3. Manual reset is achieved by clicking the RST switch to trigger the south bridge with a low level. After the south bridge works, the device returns to its original state and starts again, which is manifested as a restart. 　　　Example: Reset circuit inspection process　　　　1. Check whether there is a high level of about 3.3V at the RST switch. If not, check the line from the red line or orange line to the RST switch 　　　　. 2. When short-circuiting RST, measure whether there is a low level triggering the south bridge. If not, check the line from the RST switch to the south bridge. 　　　　3. If all reset test points have no voltage jump after short-circuiting RST, it means that the south bridge is not working. Check whether other power supply clocks are normal. If the power supply clock is normal, the south bridge is broken. If only individual test points are abnormal, check the line between the abnormal test points and the south bridge. The repair process for motherboard that does not reset is as follows　　　　 : 1. Check whether the reset circuit is normal. 　　　　 2. Check whether the equipment involved in the reset is normal 　　　　 . 3. Check whether the power supply and clock of the equipment are normal. 　　　　 4. Judge by the reset light on the motherboard diagnostic card. If it is normal, the reset light of the diagnostic card will flash at the moment of power on, or flash continuously while repeatedly clicking RST. If it is always on or not on, it means that the reset is abnormal. Perform repair according to the principle of power supply first, then clock reset. Repair methods and precautions　　　　: 1. Fragile components: gate circuits, transistors 　　　　. 2. The motherboard resets abnormally when some motherboards do not add CPU or dummy load 　　　　. 3. Whether to repair the reset circuit. The motherboard power supply, clock, gray line and other circuits are completely normal, but the motherboard still does not reset. 　　　　4. The device reset signal of most motherboards is provided by the south bridge, and some motherboards do not go through the south bridge and directly provide the reset signal by the gate circuit. 　　　　5. For most motherboards, measuring the CPU PG test point is equivalent to measuring the input end of the reset circuit inside the south bridge.