Use a voltmeter to check if there's 20V DC at the output plug of the charger.
If the charger is OK then perhaps the DC In jack is faulty.
Here's the hardware maintenance manual for the laptop.
Go to p.58 to view the procedure to remove the DC In cable. When it is out you can test if the jack is OK by using an Ohmmeter to prove continuity between the input and the output of the jack. Alternatively, if you just disconnect the jack cable from the motherboard and connect the charger to the jack's input you can check for voltage between the red and black wires of the cable on the jack's output.
If the DC-In jack is faulty it cannot be repaired, it has to be replaced.
There are two DC-In jacks available for your model and they are slightly different to each other.
The part numbers are 90205112 & 90205113.
Search for images of each part online by using the part number only to verify which one is used in your laptop and then order the part from the supplier that you suits you best