It may happens that upon switching from HDMI cable to SCART, your PS3 console no longer display images. This may be due to the fact that your console is unable recognize the SCART connection automatically.
The solution is to reset the display settings of your console (PS3 Slim, Fat, Ultra Slim).
Turn off your PS3 and connect it your your TV using the SCART cable.
Hold down the Power button for a couple of seconds until you hear a 2nd beep.