The past Monday I received my first Pi0. Today, I think I have burned

In my intention of displaying the composite video, I have soldered two pines to the TV and ground GPIO, just as the show here:
http://www.modmypi.com/blog/how-to-add- ... ry-pi-zero
What I did not know before plugging in everything, is that you mustn´t connect more than 3.3v to the GPIO.
This was the set up, following this steps:
1- Connect the gpio pines to the display.
2- Connect the 12v that the display needs for test if it shows the installed Retropie on the SD Card (at this point I think it has been when I have burned the Pi0).
3- Connect the power suply of the Pi0 (5v).


I assume that my mistake was the same as this one:
https://www.raspberrypi.org/forums/view ... 28&t=66319
Could maybe have also been a breakdown voltage for not putting tape to the cables?

You guys think it has been as I have said?
How do you connect the displays to the Pi0? I may have missed some indications?
Anyway, I have just ordered another Pi0, as you learn from your own mistakes, right?