service manual is available here
https://elektrotanya.com/lg_pf1000u-na_chassis_fm52b_sm.pdf/download.html
Not sure it will help you.
There is a chart on pg 18. About as far as you will probably get is to eliminate the adapter as the problem. Hopefully, that is what it is, because it would be easy.
If not, you would have to follow the schematic to locate a bad part. The chart only goes to assemblies, which would be a pricy repair.