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Hello everyone, in this lesson, let's take a look at the maintenance process that does not trigger a fault

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It's actually not in a particularly strict order

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The order here is listed in chronological order

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But this order is actually not the optimal order, but it is the most understandable for novice maintenance

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We can check from front to back according to the serial number on the table

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We come across a mainboard that doesn't trigger a fault, first check its VCCRTC

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VCCRTC can be measured on the common cathode diode near the coin cell

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We only need to find this common cathode diode to measure VCCRTC

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The voltage of VCCRTC is generally around 3 volts

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If this voltage is not normal, we first need to measure whether it is shorted

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Because this voltage is mainly connected to the PCH,

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there is a high probability that the PCH is damaged.

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Of course, it is also possible that the capacitor or some other small chip is damaged.

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We can directly use the burn-in method to repair

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If it is not shorted, but its voltage is not normal

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That means there is a problem with its generating circuit,

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we have to check the drawing or circuit

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Find all the way from the button battery to the VCCRTC generation circuit

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Under normal circumstances, it is caused by the damage of a certain component in this process.

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Next we can measure RTCRST#

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RTCRST# It is also a voltage of about 3V

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It can be measured on the CMOS of the mainboard

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If this voltage is abnormal, we first need to measure whether it is short circuited

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If it's shorted, it's usually a bad PCH

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There is a small probability that the capacitor may be damaged.

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If it is not short-circuited, but the voltage is abnormal,

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it means that the circuit that generates this signal is abnormal,

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or the capacitor connected to this signal has leakage.

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Next, let's look at the clock of the RTC circuit

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The clock for the RTC circuit is a 32.768 kHz magnetic

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This clock can be measured on the two clock output pins of the RTC crystal

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In general, its two pins need to have a voltage of about 0.1V to 0.5V

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If the crystal oscillator of the RTC circuit does not start to oscillate, and VCCRTC and RTCRST# are normal

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Then generally the PCH is damaged, or the crystal oscillator is damaged.

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Next is VCCDSW_3P3

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This is the deep sleep standby voltage of PCH, 3.3V

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If this voltage is not normal, you first need to measure whether it is shorted

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If it's shorted, we need to use the burn-in method to repair it

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If any chip gets hot, it means that the component is damaged.

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If it is not short-circuited and its voltage is abnormal,

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then generally there is a problem with this generating circuit

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The generation circuit of VCCDSW_3P3 is relatively simple,

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usually the purple 5V is converted by a voltage regulator tube

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Then we have to check whether the purple 5V and the voltage regulator tube are normal

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Next DSW_PWROK

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It is a good signal for deep sleep standby of PCH, sent to PCH by IO

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Under normal circumstances, as long as the IO has power supply,

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it will send out this DSW_PWROK signal

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If there is no DSW_PWROK signal, then generally the IO is working abnormally.

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Its working conditions are not met, or the IO is simply broken,

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or the external circuit pulls down the DSW_PWROK

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Next VCCPRIM_3P3

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This is the main standby 3V of PCH, and its voltage is also 3.3V.3V

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If this power supply is not working properly, we first need to measure whether it is shorted

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If there is a short circuit, we can directly use the burn-in method

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If it is not short circuit, generally there is a problem with the generation circuit of VCCPRIM_3P3

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If we lack experience, we need to check the drawings to see how the voltage is generated

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Next is VCCPRIM_1P0

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This is also the main standby voltage of PCH, the voltage is 1V

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If this voltage is not normal, we first measure whether it is shorted

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If there is a short circuit, burn the machine directly

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This voltage short circuit usually means that the PCH is broken.

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If the voltage is not short-circuited and the voltage is not normal,

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then generally the working conditions of the circuit that generates the power supply are not met,

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or the circuit is damaged.

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Next RSMRST#

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This is also a 3.3V high level sent by IO to PCH

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If the voltage is abnormal, it is usually because the IO is broken,

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or the external circuit pulls down the signal.

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Further down, the switch signal enters the IO

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We need to measure whether the switch signal has a high-low-high jump when it is pressed on the IO pin

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If there is no jump, it means that the IO to the power button is disconnected

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Further down PWRBTN#

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This signal is a wake-up signal that IO will send to PCH after receiving the switch signal

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When the working conditions of the IO are met and the switch signal is also sent to the IO,

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then the wake-up signal should also have a high-low-high jump

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If there is no jump, generally the IO is damaged.

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Next SLP_S3

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It is a status indication signal sent by PCH, which needs to be given to IO

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If the above conditions are all normal, but after PWRBTN# is sent, PCH does not return SLP_S3#

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In general, the PCH is damaged.

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Of course, it is also possible that a certain working condition of PCH is not satisfied.

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The last one is PS_ON

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It's the green line

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After IO receives SLP_S3#, it will pull down PS_ON, and also pull down the green line,

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so that the power supply starts to work

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If SLP_s3# has been sent to IO, but PS_ON has not been pulled down, it means that IO is damaged

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Of course, it is also possible that the IO to the power interface is disconnected.

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It is a very classic fault that the PS_ON is not pulled down due to the disconnection of the IO to the power interface.

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Well, the above is the maintenance process that does not trigger the fault

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For novices, we just check in this order

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After we have a deeper understanding of timing and circuits,

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we can change the order of detection according to our own understanding

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Okay, that's it for this lesson.