UE32D4000 Samsung TV: off-color upper third after while?

Hey all,

wanted to see if any of you perhaps have an idea on what’s wrong with my TV - it’s an older Samsung model and after being on for a while, the upper third stars flickering and eventually sets to be off-color, with a heavy green tint. Everything else functions normally and it’s exactly a third of the screen. What’s weird is that this was completely gone after the TV was off for 3-4 weeks and I thought it was gone completely, but it appeared again and now happens after 20-30 min of the TV being on. So I’m thining

• Broken graphics chip? Need to replace the whole board? Overheating? But why was it okay for weeks after being off for a month?
• Bad flex cable? But then why only after 30 min?
• I assume it’s not a panel problem it only happens after 30 min?

It’s regardless of input, too. Hope some of you have an idea. Many thanks!