In this video we repaired the motherboard of the LENOVO IDEAPAD S340-15IML laptop
The motherboard model of this laptop is LA-H104P
The problem with this laptop is that it works without displaying an image on the screen (black screen)
When connecting the motherboard to the power supply in standby mode (standby) it draws 22 milliamps and when pressing the power button and the board works it draws a constant current of 270 milliamps!!
When connecting the RAM voltage tester, we find that all voltages are lost except for the VPP voltage
First, we attached illustrative (anatomical) pictures of all the circuits with their operation and the typical voltage values on their outputs.
We started the repair process by measuring the voltage on all circuits and it turned out that all voltages were present except for the RAM and processor voltages.
Since the RAM voltage precedes the processor voltage in appearing, we decided to start from the RAM circuit in the repair process.
We moved to the motherboard schematic, specifically to the RAM power circuit, and we analyzed this circuit and looked at the input voltages and the most important signals necessary for this circuit to work.
After that, we measured these voltages on the IC managing this circuit to find them present and intact. By measuring the impedance on the coil of this circuit, we obtained a very low impedance (10 ohms), and this is conclusive evidence of a major defect in this circuit.
To confirm the reason for this circuit not working, we measured the circuit output using an oscilloscope and noticed that no voltage appeared even for a fraction of a second!
This prompted us to replace the IC.
After replacing the IC, we repeated the inspection and measurement process to find that the impedance was also low and the device did not work with a difference in the drawn current, and the RAM voltage also appeared incorrectly!! Here we moved to suspect that the cause of the failure is either in the processor or the RAM integrated into the motherboard because this circuit is responsible for feeding the RAM and the memory controller inside the processor (we proved this through the board view)
Then we decided to inject voltage into the output of this circuit in order to confirm the cause of the failure, and while welding the injection wire, we noticed a defect in the upper MOSFET of this circuit!
The damage to the upper MOSFET is evidence of the main voltage crossing into the circuit, and therefore there is a high probability of damage to the RAM as well as the processor due to this defect
To make sure, we decided to cancel the RAM integrated with the motherboard in order to limit the possibilities
Before starting the process of canceling the integrated RAM, we also replaced the IC for this circuit for reasons that were mentioned in detail in the video
After replacing the damaged MOSFET as well as the IC for the second time and conducting a circuit check, we noticed the appearance of all the efforts and the circuit working in a stable and normal manner, but the motherboard did not work with a noticeable increase in the current draw from the power supply, but this current is a constant current indicating that the motherboard stopped at a certain stage and did not pass it!
We then cancelled the built-in RAM using the diagram and repeated the testing process, but unfortunately the motherboard did not work either, as it also drew a constant current, indicating that it stopped at a certain stage!
Here we have finished the first part of the video on the repair process of this motherboard. We hope that you will interact with your comments and see you about this malfunction and what are the reasons that led to the board not working.
We hope you enjoy and useful viewing.
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