Laptop Model: DELL14-7447
Board Number: DA0AM7MB8D0
Fault : Not charging
Repair Process:
The system showed that the battery power was 75%, but the adapter
was connected. Everyone knows about choosing an adapter when charging DELL
laptops, so the customer bought several original adapters, but none of them
worked. It seems that the adapter has been excluded.
The battery can also be recognized. It is also
possible to start the computer with the battery alone, and it still has 75%
power, so the battery is excluded.
When restarting the computer, it says that the adapter is not the
original one, and the wattage of the adapter cannot be recognized in the BIOS
interface.
Since it is not charging, you must first measure the common point
voltage, battery voltage, charging chip conditions, and open the drawing.
As shown in the picture, the common voltage is normal, the battery
voltage is 11V, and the charging chip is BQ24737. All conditions are normal.
The EC can also identify the battery information through the bus, so it stands
to reason that it can be charged.
The charging inductor is not plugged in and the battery is 2.4V.
The battery is 11V. Many people think that 11V is not already charged?
But don’t forget that the battery is good and has electricity
inside it. Is the electricity in the charging inductor coming from the battery
itself or output from the charging circuit? You can actually measure it with an
oscilloscope.
As you can
see, the voltage at the front end of the inductor is a straight line, not a PWM
waveform. Therefore, the 11V of the inductor is the battery's own and not
output by the charging circuit. Therefore, the charging circuit is still
faulty.
At this time,
I am thinking about it. I plugged in the original adapter but it still says
non-original adapter. Is there something wrong with the adapter detection
circuit? Let’s measure it now.
You can see from the picture that PR14 has been corroded, and the
corrosion is quite serious. I used a soldering iron to remove the resistor, and
the pad below was corroded and almost fell off.
After repairing the points, I removed a 10K resistor from another
motherboard and installed it, which solved the problem perfectly. Then I
measured the charge. The front end of the inductor has a perfect waveform.
The power of the adapter was also recognized in the BIOS, and it was prompted to charge after entering the system.
Happy Reparing !!
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