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Hello everyone, today we will learn the block diagram of the boot circuit

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of the domestic computer Loongson mainboard

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Its boot circuit block diagram is like this

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This LS7A1000 is called a bridge chip

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This LS7A1000 is called a bridge chip

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RTC power supply, RTC reset signal, and clock signal

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And its main standby power supply ACPI_3V3, and 1.1V standby voltage

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After the standby power supply is normal,

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a standby voltage good signal will be generated, RTC_RSMRSTn

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The last condition is ACPI_BATLOWn, which is a low power indicator signal

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Normal standby state should be high level

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There is no way to find the measurement point for these two signals without a circuit diagram

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We have introduced its main standby power supply and the condition measurement point

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of the RTC circuit in the previous course, and we will not repeat the introduction here

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IO standby conditions, we have also introduced in detail in the previous course

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It must meet the standby power supply, clock and reset, and read the program to configure the pin,

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it can work normally

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When the standby condition of the IO and the standby condition of the bridge are normal,

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we can press the switch

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In normal standby state, this switch pin is a high level of 3.3V

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This is a switch pin header on the front panel

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The top side is the 1st foot, and the bottom is the 2nd foot, counting from this direction

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Pins 2 and 4 are power indicator lights

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Its 6th and 8th feet are power switch pins

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Pin 1 and pin 3 are the hard disk work indicators

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Pin 5 and pin 7 are reset signals, connected to the reset button on the front panel

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The 9th pin is empty

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This is the pin definition of the front panel

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This switch signal is high in the standby state

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When we press the switch, the switch will connect this switch signal to ground,

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pulling it down to low level (0V)

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After we let go of the switch, it goes back to high

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We call this a "high-low-high" transition

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Press the switch to generate a "high-low-high" jump and send it to the IO

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IO will send ACPI_PWRBTNn (also a "high-low-high" jump) to the bridge

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When the bridge is under the normal condition of the 7 major standby conditions and receives this trigger signal,

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it will set high ACPI_S5n, ACPI_S4n, ACPI_S3n and other signals to the IO in turn.

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After the IO receives ACPI_S3n, it will pull down the PS_ON# power-on signal,

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directly or indirectly pull down the green line of the ATX power supply

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Once the green line of the ATX power supply is pulled low,

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the ATX power supply will start and output orange 3.3V, red 5V, yellow 12V, blue -12V...etc.

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The output supplies power to each circuit of the mainboard

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Then the ATX power supply outputs the PG signal from this gray line and returns to the IO

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This completes the power-on

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When we repair this kind of non-starting failure,

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we should refer to this starting circuit block diagram for maintenance.

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For a mainboard to be turned on, the IO and the bridge must meet all the standby conditions,

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it must receive the switch signal, and the switch pin must be at a high level

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Then, the bridge piece receives the switch signal and sends ACPI_S3n, ACPI_S4n... and other signals to the IO

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And the IO can normally pull down the green line,

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the ATX power supply can output the power supply of each channel,

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and return a PG signal

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This completes a power-on

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Carry out maintenance according to this sequence and process

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Which signal is abnormal, we have to check its corresponding conditions

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For example, the bridge

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Its standby condition is normal. After receiving the switch signal,

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if it cannot send ACPI_S3n and other signals,

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we have to consider whether the bridge is damaged, or the IO condition is normal.

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ACPI_PWRBTNn cannot be issued after receiving the switch signal, should we consider replacing the IO?

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Do you want to continue to query the standby condition of IO?

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This is the basic maintenance idea

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Ok, here is the block diagram of the boot circuit of this mainboard