Probably a bad ac power adapter. Have you checked the output voltages
with your dmm on the power adapter plug yet?

If that is good, then the only repair you could make would be to make
sure the power plug on the motherboard is still good and does not have
cracked solder connections.

You won't get a schematic for a laptop motherboard at any price. The
replacement part is the entire motherboard.

A very experienced technician may be able to determine the extent of
the power supply failures on the motherboard, but likely won't be able
to repair anything beyond the most simple as the parts and schematic
are not available.