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Voltage input:
The first voltage that rises on the motherboard can come from two places:1. Charger
2. Battery
When we talk about input circuit, we refer to DCJACK (component where the charger is plugged). This circuit protects the voltage of the charger, besides, of course, distributing this voltage to the rest of the motherboard circuits. The high voltage (from the charger) is the first voltage that rises on the motherboard.
It is the source, that is, responsible for feeding primary sources, which in turn feed the secondary sources (which will appear after pressing the power button). It is very common for components that remain in the input circuit to have defects, especially short, as this is where the highest voltage on the motherboard circulates.
It all starts with the DCJACK power connector. As I mentioned, this connector is one of the points through which the motherboard is powered (the other is the battery). In the same line there are overload protection components, such as diodes and resistors, in addition to noise filtering capacitors, so that the high voltage arrives clean (without variations) in the other circuits.
In figure 1 we have an example of an input circuit. The high voltage (19v) can be measured on pins 3 and 4 of the DCJACK (JDCIN1), following the reference fuse PF101, then arriving at the inductor PL101.
From then on, this voltage will be called VIN or B+ depending on the project.
On 99% of the laptop motherboard there are two Mosfets (marked in red in photo below) that are in the input circuit, they are responsible for switching (passing from one side to the other) this voltage to supply the other circuits.
Well, for that to happen there is a more detailed process. However, you now need to understand the basis of how the input circuit works.
It's like learning to drive, you just need to start the car, shift and go straight. Over time you will learn more details about the car and how to follow other paths. Power Section: This includes the VlN circuit, battery charging circuit and Battery discharging circuit.
Through the schematic diagram in page 29 (charger IC), there is an information about Power Jack and Battery. Circuit charger is a main gate power regulation sourced of battery and adaptor.
Sometimes people confused how to find about "where is the Power IC in a laptop? ", because IC charging 3V and 5V, VCC core is an IC too. With the different function and ways is working, so where is a correct IC power? In this page, I will explained with a simple description about basic of that circuit.
Voltage from DC Jack with P11 that sourced from adaptor entered into PC85 and PC84 are arranged in parallel which works as noose filter with the term voltage VA then enter to PL6 and after through PL6 it changed name to VA1. PL6 function is temporary saving a charge. If we add a fuse in this circuit before the voltage entered to PL6 maybe will be good, but we see another component diode after PL6 that protect and block reverse flow so a problem adding fuse will be solved. And other that, diode function for eliminate AC voltage from inductor.
Conclusion of the figure is voltage name 19V (it depend on laptop adaptor 19V-20v-18,5V, etc) will be changed when entered a component or circuit one and the other.
DC# is command sign from EC from page 27 schematic, signal from EC will command P-channel gate to open gate if there a problem at circuit. This is called a Circuit Protection and in upper level will cooperate with selector circuit.
Circuit works as a control or signaling technique as the detector whether the voltage comes from an adapter or a battery or even both of them for the charging system.
Charger Circuit :
System charging: there are two important components in the charging system, EC and IC charging itself. EC will cooperate with the IC charging for detection and battery charging systems which are crucial, in this case also step-down N-channel MOSFET in the charging circuit, the N-channel is often problematic. See at the picture upward. In addition to EC and IC, charging inputs sourced from always voltage 3V (3V and 5V
systems) play an active role as EC mover (AC in). This is the signal that will be a condition of employment EC command voltage driving GPIO port, and then after the EC active always systems 3V and 5V result a voltage and this process of mutual integrating throughout each other up to the VS system (power switch).
Primary Sources 3V and 5V:
After the high voltage (19V) passes through the input Mosfets, as we saw in the previous chapter, it needs to reach the other circuits on the motherboard, mainly the primary PWM IC (which will generate the 3V and 5V voltages) as shown in next photo.
In the photo above, the main components that form a switched source are circled. We will see this type of font on several pages of the schematic diagram.
In this case, the square component in the center is the primary PWM IC. On its right side is the 5V supply complemented by the high, low Mosfets and an inductor. On the left side is the 3V source also complemented by the high, low Mosfets and an inductor.
But after all, what is necessary for the Primary PWM IC to work and release the two voltages (3V and 5V) in its inductors?
In photo this IC is PU401 (identification on the motherboard). There are several types of ICs for this on a laptop motherboard (as we said, each source uses a PWM IC).
Knowing this, it is necessary that you understand how the main (most used) models of this IC work.
With the knowledge we’ll learn next, you’ll be able to repair almost any laptop.
In order to work, a PWM IC depends in a practical and summarized form of supply voltage and enabling pulses, as we will see in detail below.
When analyzing the Primary PWM IC, check with a multimeter on the DCV20V scale:
1. If you have the main supply (called VIN) which is the high voltage (19V).
2. If you have the two voltages we call the regulator voltages (VREG3 = 3V, VREG5 or LDO = 5V).
3. The enabling pulses (ENTRIP or EN or ON = 3V), these signals may have a small change in name depending on the project.
4. The reference voltage of the IC operation (called VREF = 2V).
These are the terminals that usually give problem in 99% of the Primary PWM ICs. If all of these items are ok, then the IC should work.
The next important components to be tested on a switched source are the high and low Mosfets, they also tend to be defective more often. To perform a Mosfet test check the complementary material.
If the high-low Mosfets are also good, then you should test the filter capacitor of the source in question. It is a larger capacitor that is used to prevent fluctuations in the voltage of the source.
As I mentioned, a motherboard is divided by switching sources. This division ended up facilitating the search for defects that eventually happen in laptops.
It is important to keep in mind that there is no diagnostic prescription for each defect.
A laptop that does not turn on, for example, may have different diagnostics, it may simply be the defective charger. Do not think that for every laptop you are going to fix with this symptom you will necessarily find the same problem.
There are methods that we can follow through a good understanding and analysis of the schematic diagram, which will help to speed up the repair. And that is what you will learn in this forum.
5 Voltage and 3 Voltage Power Section:
If we want to find the layout of 3V and 5V systems in the schematic diagram on the first page there is a schematic diagram of the system description 5V/3V PCU, then open the pages. In this case there is on page 30, below an example.
From a page 30 you know information of the type of IC used and the circuit contained in the page and Project Description / Name Circuit.
3V & 5V circuit system is included into the System Standby and Dual Mode. System standby is the system input and output circuits will be active although the SW button not yet in press.
There are two system standby circuits in the motherboard "charging circuit and circuit 3V and 5V".
From image noticed, it is the system 3V and 5V dual mode whereby this circuit will work after on-off button on the press after receiving the command signal from the EC ( S5_ON ) output of this circuit for the power needs usb, hdd, dvd and etc. See power sequence below:
Charging Source - battery Section:
Battery charging circuit (charge) is responsible for recognizing and charging the battery. It is the one that controls the power supply to the motherboard when the charger is not connected.
In photo, the charge circuit is basically formed by the IC PU301, by a high Mosfet (PQ311), a low Mosfet (PQ314) and an inductor (PL301).
It is in the charge circuit that we find the famous MOSFET SWITCH, which switches the voltage of the battery and that of the charger, making sure that they do not collide.
The operation of the switch Mosfet is very simple. Imagine that you have a laptop connected with a charger and battery connected, at that moment the battery is in the background being charged and the charger is feeding the entire motherboard. If you remove the charger, the laptop will continue to be powered by the battery voltage thanks to the switch Mosfet.
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