Samsung qn55q6 went pop, no picture, replaced power board, now lines

If something went pop, that sounds like some sort of catastrophic failure. If it was a noticeable POP, usually that's the sort of damage you would be able to see. Did the original power supply board have any components that looked like they had failed?

The other thing to keep in mind is that if it was the power supply board that was the initial cause of the issue, those sorts of things can take other components out with them depending on the exact nature of the failure. So even if the power supply was the initial issue, it may have damaged the system board on the way out.

It sounds like you're getting different results than before you replaced the Power supply board, and I am not intimately familiar with TV repair, but this still seems like more than just a cable issue.