@Alessio2001, I ran into this same problem on my last Arcade conversion. The issue ended up being on the CRT side. You should have a control board with 6-8 knobs. Mine was a small square one, but they can be different. This controls the image on the CRT. You can use this to change the Vertical Hold (height), Horizontal Hold (width), and contrast, and some have R/G/B knobs. One of those, when you change it in one direction, made my image duplicate, flicker, and rotate on the screen. When I turned it in the opposite direction, it solidified into a single image rotating from top to bottom. Eventually, it would slow down and stop in the middle of the screen.