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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 XR models

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Step 1, open the component map and find the location of the backlight power supply

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Step 2, determine the position number of the backlight power supply in the bitmap

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

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and find the corresponding signal

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Step 4, jump to the bitmap according to the pin identification,

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we can view the connected components and measure the voltage or diode value according to the yellow position

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First, we open the component map, circuit diagram and bitmap of the iPhone XR

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Find the backlight power supply in the component map

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The display of the iPhone XR is 6.1 inches,

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so it will have two backlight chips

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The backlight power supply of the iPhone XR has no logo

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These 2 chips are the backlight power supply chips

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The position number of the backlight chip can be determined according to the bitmap

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The search method of these two groups of backlight chips is the same

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Let's take U5660 as an example to search

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Enter U5660 in the schematic diagram and click Search

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After finding the backlight chip, find the corresponding signal

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Let's find the power supply of the backlight power supply, PP_VDD_MAIN main power supply,

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and the booster inductor of the backlight boost circuit,

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the boost diode and the backlight power supply

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In the schematic diagram, pin D4 is the power supply for the backlight power supply

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Connected to the main power supply,

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the main power supply will also be connected to the inductor L5662,

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and then connected to D5662 after the inductor

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L5662 and D5662 are inductors and diodes used in the backlight booster circuit

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After the power supply passes through the diode, it becomes the backlight power supply,

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and the backlight power supply is connected to the display seat

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Jump to the bitmap according to the name,

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you can see that the backlight power supply is directly connected to the 9th pin of the display seat

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When judging whether the boost inductor and diode of the backlight circuit are good or bad,

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you can jump to the bitmap according to the position number,

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you can find the boost inductor

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When measuring the quality of the boost diode,

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jump to the bitmap according to the position number,

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and the yellow point in the bitmap can be measured

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Let's find the backlight power on signal

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In the schematic diagram, the D3 pin of U5660 is the open signal, HWEN

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The open signal is connected to the 1.8V power supply,

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and the power supply of the power supply is used as the open signal

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Jump to the bitmap according to the name,

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the power supply will be connected with the power supply of CPU, Wifi and other chips

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In actual maintenance, the probability of the signal being damaged is relatively small

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Let's find the I2C bus

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The I2C bus is issued by the CPU

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In the schematic diagram, pins B2 and A2 of U5660 are I2C buses

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Jump to the bitmap according to the name,

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

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The I2C bus of the backlight power supply will be shared by other circuits

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Another I2C bus is also connected with other components

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Let's find the DWI brightness adjustment signal

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The signal is sent by the CPU to the backlight chip

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In the schematic diagram, the C2 and C3 pins of U5660 are DWI bus,

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and the bus is divided into data and clock

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Jump to the bitmap according to the name,

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you can see that the bus will reach another backlight chip at the same time

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These 2 sets of backlight chips will work at the same time when turning on

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Clock signal for DWI bus

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Jump to the bitmap according to the name,

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the clock signal also reaches the two backlight chips at the same time

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The clock can be measured at resistor R5650

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Let's find the SW frequency adjustment pin of the backlight power supply

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In the schematic diagram, the C4 pin of U5660 is the SW1 frequency adjustment pin

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This pin mainly controls the diode turn-on and cut-off of the backlight boost

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The backlight power supply passes through the LED inside the screen

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and then returns to the backlight power supply

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Let's take a look at the physical shape of the light-emitting diodes inside the screen

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This is the screen of the iPhone 11, which is similar to the screen of the iPhone XR

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There will be an LED light strip at the bottom,

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two cables are connected next to it,

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which is the backlight power supply and feedback

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When the backlight voltage is normal,

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it will be connected to the LED inside the screen

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After a current flows through the light-emitting diode, the screen is lit

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Let's look at the CAT1 and CAT2 of the backlight power supply returning the backlight power supply

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after passing through the internal diode of the screen

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In the schematic diagram, pin C1 of U5660 is backlight feedback 1,

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pin B1 is backlight feedback 2

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Jump to the bitmap according to the name,

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CAT1 is connected to the 11th pin of the display seat,

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and CAT2 is connected to the 7th pin of the display seat

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Backlight feedback can be measured through the display connector

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When a pin of CAT is disconnected, it will lead to light and dark screen

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

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In this way, we have searched for all the important backlight signals of the iPhone XR model

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Ok, that's all for this video