In this class, we will talk about the circuits related to the failure of no display

So what should we consider first for this display circuit?

This is the display connector, we can think it as a display

It first needs to get a power supply, 1.8 volts, usually from the power chip

Then, the CPU enables detection, detects the screen, and resets the screen

Then, the DSI bus starts to work,

and the CPU sends the turn-on signal ENP ENN to the display chip

ENP is the turn-on signal for positive voltage,

and ENN is the turn-on signal for negative voltaage

Then at this time,

the display chip can output positive and negative voltages to supply power to the screen

The CPU sends the turn on signal to the backlight chip

The backlight power supply chip outputs LED+ power supply to the screen backlight assembly,

such as 14V to 21V power supply

At this time, the screen basically lights up

The CPU transmits the image data to the display screen through the DSI bus

At this time, the display screen can display the picture,

and the synchronization signal is output to the CPU

This is the workflow of the display circuit as a whole

The circuits related to the no display fault are the circuits in the workflow

The display chip here is actually a screen power supply chip

The backlight chip is a backlight power supply chip,

it just provides power conversion

This is reset,

this is detection,

this is synchronization,

this is bus, also called communication protocol

The whole circuit is mainly composed of these, including the CPU

The image processing is mainly handled by the CPU

Generally in the maintenance,

we don't need to think too much about the CPU,

and we don't think about it unless it is touched

What is the concept we need to know

The principle tells us that the power supply is provided by the power chip to the display screen

There is a problem with its line,

such as this power supply 1.8 volts does not exist

That is, if we can't measure 1.8 volts on this line,

then we're suspecting the power supply

This is the essence of the maintenance ideas

In the same way, these power supplies,

including these power supplies, are the same,

and the maintenance, measurement, and analysis methods are the same

What I said just now is that there is an open circuit in the line,

or there is no open circuit but there is no voltage

In reality, there will also be a short circuit

For example, this point is shorted to ground,

which proves that the components on the circuit of the power chip have a short circuit to ground,

and we will analyze it

All analysis methods of power supply are the same,

measuring voltage, measuring ground value

These three chips mainly provide power

The rest are general signals, such as reset signal

What about reset as we mentioned earlier,

if I measure 1.8 volts, it is basically OK

You can also measure its ground value,

because it leads to the CPU

If there is no problem with the measured ground value,

it basically has no problem

For the specific reference to the ground value,

generally some drawings will give a rough value, including the detection signal

All signals can be judged in the same way

The display connector is connected to the CPU

No matter what signal is on the line,

we can use one method to judge,

that is to measure the ground value

The ground value can measure whether the CPU is soldered or not,

and whether there are any problems with the components

In the same way, when we judge the quality of the bus,

we can also measure the ground value

When measuring the ground value,

the black test lead is connected here, and the red test lead is grounded

We find its specific pin by measuring the ground value of this point

Of course it has about 8 wires, we just need to find one of them to measure

For example, by measuring the ground value of this point,

we can measure whether the CPU is soldered,

whether the components connected in series are soldered,

or whether the line is disconnected

If we measure that the ground value is OK,

it proves that there is no problem with this bus

Well, we learned which lines are related to the fault that the phone can be turned on but no display,

including the general analysis method of measuring the line

Okay, that's it for this lesson