The QN90C is a high-end Neo QLED set where repairs can be worthwhile if the failure is confined to electronics rather than the panel/backlight system. Power supply or HDMI board repairs may be economical relative to the purchase price, especially early in ownership.
Replacement becomes more compelling if the issue involves uniformity defects, widespread dimming-zone artifacts that indicate backlight driver trouble, or persistent panel faults like lines or large dead areas, because those can be costly and sometimes recur. Given the premium price, it's important to confirm warranty status and whether the TV has seen power surges; repeated power events can damage multiple boards.
If the TV is older and needs both backlight-related work and a main board, the combined quote can cross the threshold quickly, tipping toward replacement.