1

00:00:01,033 --> 00:00:04,933

In this lesson we are going to focus on backlit power supplies

2

00:00:06,933 --> 00:00:10,266

A backlit power supply is also called a light controller,

3

00:00:11,133 --> 00:00:13,066

they all refer to a chip

4

00:00:18,166 --> 00:00:22,333

The main function of the backlight power supply is providing an operating voltage

5

00:00:22,333 --> 00:00:24,566

for the backlight of the LCD screen

6

00:00:25,633 --> 00:00:27,466

The chip generates power that then

7

00:00:27,466 --> 00:00:30,500

powers the light-emitting diodes inside the display

8

00:00:31,966 --> 00:00:33,333

When the diode is powered,

9

00:00:33,466 --> 00:00:34,933

the screen will brighten

10

00:00:36,166 --> 00:00:38,866

Now let's look at the LEDs inside the screen

11

00:00:41,900 --> 00:00:44,000

This is the iPhone 11 model

12

00:00:44,433 --> 00:00:46,166

After taking the screen apart,

13

00:00:46,633 --> 00:00:49,933

we can find that there is an LED light at the bottom

14

00:00:51,200 --> 00:00:54,133

The backlight chip provides power to this tube,

15

00:00:56,766 --> 00:00:59,533

and when the tube is powered, it lights up,

16

00:01:00,500 --> 00:01:02,866

and then it lights up the whole screen

17

00:01:04,366 --> 00:01:06,933

This is the LED under the microscope

18

00:01:10,733 --> 00:01:13,866

A damaged backlit chip can cause two failures

19

00:01:15,033 --> 00:01:16,666

The first is the dark screen,

20

00:01:16,833 --> 00:01:18,966

and the second is the dark and light screen

21

00:01:19,600 --> 00:01:21,966

A dark screen is when the screen is black

22

00:01:22,133 --> 00:01:25,033

but the image information can be seen inside

23

00:01:26,200 --> 00:01:30,300

A dark and light screen means that one half of the screen is displayed

24

00:01:30,400 --> 00:01:32,000

and the other half is not

25

00:01:32,966 --> 00:01:34,600

Let's look at this problem

26

00:01:35,400 --> 00:01:37,266

If the phone shows such a picture,

27

00:01:37,400 --> 00:01:39,400

the fault is the dark and light screen

28

00:01:42,400 --> 00:01:46,066

One half of the screen is lit and the other half is black

29

00:01:46,366 --> 00:01:49,566

The dark screen fault is not easy to show with pictures,

30

00:01:49,966 --> 00:01:52,133

we can learn about it through the video

31

00:01:52,400 --> 00:01:55,833

We can see that there is an Apple logo in the center of the screen,

32

00:01:57,633 --> 00:01:59,500

and the entire screen is black

33

00:02:00,300 --> 00:02:02,500

A fault like this is a dark screen

34

00:02:03,800 --> 00:02:07,233

Among Apple's models, from iPhone 6 to 8p,

35

00:02:07,433 --> 00:02:10,800

iPhone XR and iPhone 11 use LCD screens

36

00:02:11,700 --> 00:02:13,700

Use LCD screen's models,

37

00:02:14,033 --> 00:02:16,433

the mainboard will have a backlit power supply

38

00:02:18,000 --> 00:02:20,533

For a large 5.5 inch screen,

39

00:02:20,966 --> 00:02:23,400

there are two backlit power chips in the mainboard

40

00:02:25,800 --> 00:02:29,000

A chip controls half the brightness of the screen

41

00:02:30,166 --> 00:02:34,800

With OLED screen models, the mainboard has no backlit power chips

42

00:02:35,300 --> 00:02:39,833

Because it's a cold light screen, it will spontaneously glow

43

00:02:40,800 --> 00:02:44,533

The output mode of the backlit power supply is boost output

44

00:02:45,866 --> 00:02:50,033

It turns the battery's 4V supply voltage up to about 20V

45

00:02:50,266 --> 00:02:53,766

to power an LED inside the screen, which lights it up

46

00:02:56,833 --> 00:03:01,466

Next, we go to the physical mainboard to know the backlight power chip

47

00:03:04,133 --> 00:03:08,466

The 4.7-inch model has only one backlit chip in the mainboard

48

00:03:09,066 --> 00:03:11,200

This is an iPhone 7 mainboard,

49

00:03:11,666 --> 00:03:14,066

the backlight chip is in this position

50

00:03:14,766 --> 00:03:18,433

Backlight chips are mostly square and relatively small

51

00:03:20,933 --> 00:03:23,000

The mainboard is an iPhone 8p,

52

00:03:23,666 --> 00:03:28,533

it uses a 5.5-inch screen, and it has two backlight chips

53

00:03:30,633 --> 00:03:34,666

These two chips are the backlit power chips in the iPhone 8p

54

00:03:35,633 --> 00:03:37,700

The mainboard is from the iPhone 11,

55

00:03:38,200 --> 00:03:41,900

which also uses a 6.1-inch LCD screen

56

00:03:46,166 --> 00:03:49,900

It has two backlit power chips, both inside the shield,

57

00:03:50,266 --> 00:03:52,633

which we can see when we remove the shield

58

00:03:54,700 --> 00:03:56,533

The two chips are square

59

00:03:56,900 --> 00:03:59,633

This chip is the backlit power chip in iPhone 11

60

00:04:00,566 --> 00:04:02,433

So that's it for this lesson