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iPhone backlight circuit repairing

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This video mainly explains how to find backlight circuit signals and measurement points for iPhone 11 models

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step 1

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Open the iPhone 11 component map and find the backlight chip in the component map

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Step 2, determine the position number of the backlight chip in the bitmap

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Step 3, go to the schematic diagram to search for the position number of the backlight chip,

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and find the corresponding signals

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Step 4, jump to the bitmap according to the component signal name

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The voltage and diode value can be measured at the position of the yellow point in the bitmap

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Before looking for the signal, we first open the iPhone 11 component map,

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circuit diagram, and bitmap

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Find the backlight chip in the component map

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Because the display screen of the iPhone 11 model is 6.1 inches,

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there will be 2 backlight chips in the mainboard

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The search methods for the two groups of backlight chips are the same

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Let's take one of them as an example to find

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According to the position of the backlight chip in the component map,

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find the same position in the bitmap

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Let's find out the group of backlight chip U5650

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According to the position number of the backlight chip,

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we search for the backlight chip in the schematic diagram

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After searching for the backlight chip,

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search according to the signal in the schematic diagram

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Let's first look for the main power supply and the inductor, diode,

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and backlight power supply to the display seat

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According to the identification in the circuit diagram,

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the D4 pin of the backlight power supply is the main power supply

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One way of the main power supply provides the working voltage for the chip,

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and the other way will pass through the inductors L5651 and L5652 to reach the diodes D5651 and D5652

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The above group of inductors and diodes is used as a flash when the front camera takes pictures

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The backlight circuit uses L5652 and D5652

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After the main power supply comes, it reaches the anode of the diode

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When the positive pole voltage is greater than the negative pole voltage,

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the main power supply will flow through the diode to the rear pole

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and become the backlight power supply

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The backlight power supply is connected to the display seat through the resistor R5651

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We can jump to the bitmap based on the name

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At this time, we can see that after passing through R5651,

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it is directly connected to the display connector J8000

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When we want to measure whether the booster line components are damaged,

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we can jump to the bitmap according to the position number

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According to the corresponding component of the bitmap,

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the position of the yellow point can measure the quality of the component

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When the boost diode is measured,

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we also jump to the bitmap according to the position number

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If it is not easy to measure, we can measure the components connected across the diode

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Next, let's find the turn-on signal of the backlight power supply

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The D3 pin of U5650 is the open signal, HWEN

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The open signal is connected to the 1.8V power supply

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Jump to the bitmap according to the name,

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the power supply is output by the main power supply

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This power supply will be shared with CPU, audio and other chips

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This signal will not cause problems during actual maintenance

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If there is a problem, it will not turn on the machine,

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and in extreme cases, the board may be disconnected

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Let's find the I2C bus

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The B2 and A2 pins of U5650 are the I2C buses

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Jump to the bitmap according to the name,

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the I2C bus is sent by the CPU

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In the bitmap we can see that the I2C bus will be shared with other chip

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Jump to the bitmap according to the name,

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we can see that another bus of I2C is also connected with other chips

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We can measure the voltage and diode value of the I2C bus at the position of the yellow point in the bitmap

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Let's find the DWI brightness adjustment bus

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In the schematic diagram, pins C2 and C3 are DWI bus,

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and the DWI bus is sent by the CPU

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Jump to the bitmap according to the name,

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the DWI bus of the two sets of backlight chips is connected,

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so the two backlight chips will work at the same time

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Another DWI bus is also connected to the CPU,

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and at the same time connected to another backlight chip

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When measuring this bus, we can measure at the resistor R5650

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Let's look at the frequency adjustment pin SW

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In the schematic diagram, pin C4 is SW1,

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which is used to control the diode on and off of the backlight circuit

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The backlight power supply will pass through the light-emitting diodes inside the screen

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Let's look at the physical shape of the light-emitting diode inside the screen

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This is the screen of the iPhone 11

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After disassembly, we can see that there is an LED light strip under the screen

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There are two cables on both sides of the LED light

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This cable is specially designed to power LED lights.

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When powered on, the LED lights will glow,

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lighting up the screen

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Next, let's look at the feedback CAT1 and CAT2

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In the schematic diagram, C1 and B1 pins are CAT1 and CAT2 feedback pins,

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and the feedback pins are directly connected to the display socket

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We jump to the bitmap according to the name, we can see that

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CAT1 is connected to the pin 22 of the display seat,

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and CAT2 is connected to the pin 26 of the display seat

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When we measure, we only need to measure the socket pins to know whether the feedback is normal

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If there is a broken line in the feedback, it will cause a light and dark screen

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If the backlight power supply is not generated, it will cause a dark screen failure

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Ok, that's it for this lesson