[1]
First step would be to de-solder the existing LED (labeled "D9" on PCB silk screen for P150SM) which you can see circled in yellow in the photo below.This whole process can be done without dissembling the laptop, you should only need to remove the speaker grill.
[2]
Here you will have two options when soldering your new LED, you can solder it to the pads (D9) that you removed the original LED from. However I recommend soldering the new LED to the un-populated pads (D4) to the right of the Original LED simply because it is easier. Solder 2 wires about 2-4cm long to the D4 pads marked in Red and Purple in the photo from step 1. Solder your LED to the other end of the wires you soldered to the pads so that you can place the LED directly under the power button. Take note that the pad circled in Red is the LED anode (+) and the pad circled in purple is the cathode (-) If you are not sure what sides of the LED are which you can simply test it by touching it to the pads before soldering, if it is the wrong way it simply will not light up.
[3]
Now you will want to place the LED where the original one was as shown in the picture below. You may want to tape it down with electrical tape, also make sure there is no exposed wires that could short on anything.
[4] Optional
If your speaker grill does not fit because you have used a larger LED you can sand down the light guide on the underside of the speaker grill until it no longer touches the LED when snapped into place. If you used a very bright LED like mine you may want to dim it down by adding strips of paper underneath the power button, I used 4 layers to get the brightness seen in the first photo.
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