Have the manual and training guide? If not:
https://elektrotanya.com/samsung_pn5.../download.html
It's a Zip file, and the training guide shows several panel problems and their cures. It also details the SMPS voltages and other voltages to check. That would be my first step.
When downloading the manual, wait until "processing" becomes "Get Manual" - and click on the "get manual" - choose download, and then open it with WinZip or another ZIP archive tool to get the manual(s) and training guide.
Hope this helps.