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Could you please provide a little more details as to what the device is (make and model) and what you have done to date to troubleshoot.
Are you seeing the vertical lines appear on all channels or just terrestrial or a given HDMI source, for example when you press the menu button do you still see the vertical lines.
This is the simplest way to determine if its the control board or the LCD panel itself.
The most likely cause is interference, I would start by unplugging both ends of an HDMI cable, then plug it into a spare HDMI port and then plug it into the device again but using a route where it is away from other wires and power sources.
If this doesnt work, we need to rule out a software issue.
If after restart the fault is still present, then its likely this is a hardware fault and require professional diagnostics. Please let me know how you get on with the HDMI cable and factory reset, and if need be if this doesnt resolve your issue, provide me with your postcode and I can recommend a firm who can repair the hardware fault.
I will hand this over to another expert as I am limited to what more I can suggest remotely.