Topic: Problem with a SNES mod. Help!

I've recently finished, after some difficulties due to my lack of experience, a [b]50/60 Hz mod on a PAL Super Nintendo[b], because it was given to me with the region free mod (that is lifting a single pin) done, but for some reason it wasn't able to read any of the Japanese games I bought a couple years ago.

So after successfully modifying a Mega Drive I decided to try doing the same to the SNES, in order to see if it was the problem. It was way more difficult, but I managed to do the mod, which consists of a switch to toggle between 50 and 60 Hz (I wanted to be able to play both PAL and Japanese games) and the aforementioned lifted pin which doesn't have any cable attached. More experienced people than me told me it wasn't necessary to create a second switch, that being region free always was the situation I would want for my SNES. So I didn't do it.

I tried my games and they worked, but... 2 of them, a PAL International Superstar Soccer Deluxe that used to work and a Japanese Super Mario Kart that I bought in Japan without knowing whether it worked, can't boot properly.

Namely ISS shows a "wrong region" message if I put the switch on 60 Hz (which I shouldn't, because it's PAL) or starts to boot the Konami logo but suddenly stops. Super Mario Kart shows the Nintendo logo either way, but doesn't go further.

I've obviously cleaned the cartridge pins, even opened them to check for damaged tracks or further dirt, but it wasn't the case. They don't seem to have anything wrong. They just don't work. I've been told ISS is one of the problematic games, but SMK should be fine.

And they tell me to do the second switch just in case, but I can't see the use because at least SMK should work yet it doesn't.

Anyway, could anybody please give me some advice? It not being "do the Super-CIC mod" or "play emulated". Thanks.