simple 555 pwm generator problem

[m.m.m]

Hi everybody, I wanted to make a simple pwm generator with the 555 IC.I tried this schematic on the breadboard:
http://www.dprg.org/tutorials/2005-11a/
but the output is constant 12v and the pin 7 voltage is about 6v constant. what have I put wrong?
thanks.

edit:
there are also some schematics that use the pin 3 as input for the mosfet and connect pin7 to the potentiometer, which one should I use?

[m.m.m]

solved, It turned out that two of my 555s have been damaged and don't work. used a 7555 and worked great.