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How to find short on the motherboard?

How to find short on the motherboard?​

When a motherboard does not turn on, some voltage at one of its switching sources is absent.

This can happen because some component of the circuit is SHORT.

And to find out where the problem, you'll use the same measurement logic as the motherboard's coils.

Only this time not in search of voltage, but a low resistance in relation to the ground, or better said, a short circuit.

If you place the multimeter on the continuity scale, then ground the black tip on the plate and with the red tip check the coils, it CANNOT give a result equal to zero resistance.

If that happens, then you have a short on that coil line.

So now just look at that circuit in question.

An interesting tip is to use the asymmetric source to inject voltage into the shorted line.

In this case, you only need to regulate the voltage allowed by the circuit at the source (NEVER GREATER).

When injecting voltage into a line that is shorted, the guilty component will heat up.
This is one of the facilities that the asymmetric source brings us.

2. Laptop turns on and does not give video:

Many defects will also appear on your bench with this symptom: Laptop turns on and does not display video.
Here the solution will be almost like a checklist. Just follow a few steps and you'll find where the problem is. However, many novice laptop repair technicians often find that there is a magic recipe for each defect.

So they go to the internet to search for something similar whenever they get a laptop to fix. And in the vast majority of cases this is a waste of time. You need to understand how a laptop's motherboard and peripherals work.

For that there is no miracle or magic formula, you have to study and apply the knowledge to gain experience.
The knowledge of this part is to give you a north. There is a great chance that you can solve some defects, but just take as a basis for you to study more and get deeper into the subject.

How to find the defect when the notebook turns on and does not give video? For a laptop to connect it needs all of its voltages and power supply properly working on the motherboard.
Although this seems very logical and repetitive, you need this guidance when you have a symptom of a motherboard that connects and does not provide video.

Before charging the motherboard, perform the following basic tests:

Swap memory and processor:
Most of the cases that appear with this symptom
can be solved only by testing the memory and/or processor.

Check if video appears on an external monitor via the VGA or even HDMI connection. If so, then the defect will be in the flat cable, the screen or the BGA chipset that controls the video signals on the motherboard.

Test to connect the motherboard with nothing connected (HD, DVD, wireless card, etc.).

If after all these tests the card still has no video then does the following:
Check first if the voltages are present in the motherboard coils.
If they are ok, then see if terminal (pin) 8 of the BIOS IC is powered (3V), and then rewrite the BIOS.

3. Laptop turns on and off quickly:


The symptom that we will analyze next happens less frequently relatively speaking. However, it must also be taken into account as it is about understanding the secondary and transferred voltages of the motherboard.

And this is very interesting to study.

I want you to understand the following, when the charger is connected to the motherboard, some voltages are born in it (known as primary voltages) that will cause the motherboard to be in a kind of standby state.

Just waiting for you to press the power button for the rest of the voltages to appear and the laptop to work fully.

So when you press the laptop's power button and the motherboard shuts down quickly, it is because some secondary voltage is shorted or absent, preventing the motherboard from continuing the start sequence. Knowing this, you only need to test the secondary and transferred voltages that you have on the motherboard with the aid of the schematic diagram.

Here are some examples of voltages that appear after we press the power button:
5VS, 3VS, 1.5VS, 1.8V, 1V,
among others.
How do you know if a voltage is Primary or Secondary?
The voltages that have the Acronym VALW are primary. Ex: 3VALW. It means Voltage
Always, that is, tension always present.
The stresses that have the acronym VS are secondary. Ex: 3VS. It stands for Voltage Suspend.

We saw the main defects that a laptop motherboard can have and how to solve them.
 

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