My galaxy is flickering and black screens when locked

Hi, I have Galaxy S5 and I am facing the same exact problem. The screen starts to flicker and then the screen goes black. After this you cannot see anything but the phone works just fine. It performs normally even though you cannot see anything. I am currently posting this answer from the same Galaxy S5 :D the problem still exists but you can still use the phone but you need a lot of patience using it.

So, here is what I suggest you try. The following instructions sure sound real strange but it is 100% working for me. If your phone's screen turn's on anytime the make sure that you change the "screen timeout" to 10 mins (go to Settings -> Display -> screen timeout).

Now change you screen brightness so that "Auto" is not checked and make sure that your screen brightness is always kept above 50%. Sometimes of the screen starts to flicker randomly just keep bumping up the brightness little untill the flickering stops.

(This is optional but very useful) If possible, download host for Samsung app (by TeamViewer) on to you device and TeamViewer on your PC or Laptop and create a free account and add the phone to your device list. This will help you to use your device and access it from your PC.

Here comes the strange step.

If your phone screen goes black and is not turning on. Try heating the screen (please do not place your device in microwave or oven or some thing like that) you can use a hair dryer or protable room heater (with a fan) or even your car vents at full heat. Car vents method takes a bit longer but other take from 3 mins to 6 mins at max and this is how I use my phone.

I am really surprised to stumble upon this heating to make it work thing and so I recently ordered a ifixit tool kit to try some thing I think might fix this issue. Hope I can fix it.

Cheers