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In this class, we will talk about how to repair

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when the power supply chip of OLED screen has no voltage output

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To get a mainboard, we have to take a look at its appearance

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First of all, we have to observe this chip,

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which is the chip that outputs 7.6 volts, 4.6 volts and -4 volts

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Find this chip and see if it is corroded by water

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If there is water ingress, and the phone does not display

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At this time, we can also remove the screen power supply chip without testing,

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process the pad, and then reinstall the chip

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Basically, this failure is fixed

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This is a situation

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If the chip is not corroded by water, what should we do?

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We can measure the ground value of the display chip

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The display has 3 ways of power supplies of 7.6, 4.6, -4 volts,

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we need to find where the 3 power supplies are

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Let's take Xiaomi 11 as an example,

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we can directly find its display seat,

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which is the place where the screen cable is connected

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This is the display seat, J6503,

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its power supply is in this position,

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ELVSS is -4 volts,

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ELVDD is 4.6 volts

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We can also quickly find this socket in the circuit diagram

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We click "Find Schematic Components" and it jumps here,

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J6503 is the display seat

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This seat contains a touch circuit, TS, TP means touch circuit

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It also has number cards, but who are not our concern

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Because we are repairing no display,

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we need to find a screen power supply circuit

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This is the DSI bus, this is the fingerprint,

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we don't care about them

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These are the screen power supplies, ELVDD, ELVSS, and AVDD

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We click "Find Bitmap Signal"

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It can be seen that AVDD passes through the first pin of this resistor,

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here is AVDD, the power supply of 7.6 volts

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Let's test its ground value here to see if there is any problem

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Measure ELVDD here,

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measure AVDD here,

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and measure ELVSS here,

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measure these 3 power supplies,

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and see if there is any problem with the ground value

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If we measure the ground value to infinity

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For example, when we measure the first pin

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Let's look at its lines first, it's 7.6 volts,

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This R6507 is a 0 ohm resistor,

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this end is powered by a 7.6 volts,

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then where does it go?

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It goes to this screen power supply chip, U6401,

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there are three large inductors around it

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This is the characteristic of the OLED screen power supply chip

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Let's analyze, what should we do if there is infinity

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First, infinity has nothing to do with this capacitor C6505,

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it is not considered

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Infinity is only related to the series components in this line

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This R6507 is connected in series at this end, to the point of this chip

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It has nothing to do with these 3 capacitors

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OK, let's summarize

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If we measure the ground value of the first pin of the connector is infinite,

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there are several situations

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If we measure the value to more than 600 on the second pin of R6507,

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it means that R6507 is damaged or falsely soldered

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We can directly remove the R6507 and connect its two pins with wires

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When we measure that the first pin of R6507 is also infinite

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It means that there is a problem with the screen power supply chip

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Re-solder or replace it

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After re-soldering, it is still infinite,

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then we will replace the chip

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That way, it's usually solved

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Okay, that's it for this lesson