Sega Master System mods (AV-out, 50/60Hz, language switch)

This video shows how to add AV-out on an original Master System as well as switches for 50/60Hz and english/japanese language. The language switch affects only a handful of games. Out of my collection only "Wonder Boy" and "Wonder Boy in Monsterland" showed any difference when using the switch. "Alex Kidd: The Lost Stars" displayed the Sega Mark III logo but nothing else seemed to change.