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Laptop not powering up. What are the expected voltages on the power rails?

HP Recommended
HP Notebook-15-ac107na
Microsoft Windows 10 (64-bit)

The power jack joins the motherboard at a connector marked PJP1.  There are eight pins of which seven are connected.

Starting from conductor nearest the video connector marked JLVDS1 on the mother board the first two conductors are colour coded red, these show a steady 19.55 volts when the computer is connected to the mains.  The next two conductors are colour coded black and contect to ground. The fifth pin is not connected.  The next conductor (sixth) is colour coded brown and shows a steady 19.5 Volts.  The seventh coductor is colour coded yellow and  shows a steady 0.7 Volts.  The eight and last conductor is colour coded white and shows a steady 3.2 Volts.

None of the voltages change when the power on button is pressed.  Does anybody know what the correct voltages should be on these pins and what change (if any) there should be when the power on button is pressed?

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