QQ190 no video hardware analysis

I installed a Lemon-Rx LM0037 Rx to my QQ190 RTF and replaced the stock camera with a runcam Swift RR, but the image quality was very poor.

So I tried flying line-of-sight at close range, when suddenly the quad started freaking out. It flipped and rolled in a regular pattern until it hit the ground.

Fortunately it was not flying high at this moment and fell on soft grass – not even a prop was broken…

However, I cannot get any video signal any more (not even the OSD) – the best, I can get, is narrow stripes, but I’m not sure about the channel as I used auto-search and A7 seems to be the strongest signal…

Everything looks ok in betaflight and I can control the quad via my DX7.

How can I find out, what’s wrong? What kind of analysis is available (LEDs on the powercube stack, etc…)?

Pressing the Reset button for 10 seconds did not change anything…

Best regards, Peter