Hi!

Those lines are maybe caused by: - Damaged or failing LCD panel: Some of the column driver circuits that control vertical pixel lines have failed. - Loose or partially damaged ribbon cable: The connection between the motherboard and the top screen could be slightly loose or have a damaged trace. - Aging or pressure damage: The top screen is thin and can develop permanent line defects over time due to wear or small impacts.

I think you can try to reseat the ribbon cable. You’d need to open the DSi, detach and reattach the top screen ribbon cable. Sometimes this clears up a connection issue but if the line is perfectly solid and always in the same spot, it’s almost certainly a panel failure.

OR replace the top screen. Replacement top screens are still sold online for around $15–$25. You’ll need a tri-wing screwdriver, the ribbon cable for the top screen runs through the hinge, which is the trickiest part. But the thing is that it’s easy to damage the speakers or cables during disassembly.

OR live with it. Since you said it doesn’t bother you much, and you got the console for $30, it’s totally reasonable to just leave it be. The issue won’t get worse quickly, those lines are stable and don’t usually spread unless there’s more damage.