GPIO outputs not changing on specific GPIO ports

Question

I'm using a Rpi B rev2 and I'm having problems changing the output of ports 2,3,4,5,6 (BCM). All the other ports work perfectly. I searched for documentation and I see the only thing that sets these apart is that they have a default HIGH pull resistor activated. (source: https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf)

Whatever I do (cleanup, define a DOWN pull resistor), I can't get it to change. Can somebody clarify this behavior?

PS: I use python rpi.gpio on a Archlinux Arm distro

EDIT: As per request; the code

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(4,GPIO.OUT) #per example pin 4
GPIO.output(4,1)

The voltage on the pin 4 is a 0.8V, when I change it to 0, still the same. On all other +- 20 ports this works.

UPDATE: Due to tests I ran with hooking up a mosfet, I broke a couple of GPIO pins, Joan (see above) his tool is a great way of testing your GPIO pins. Credits to him

Answer 1

GPIO 5 and GPIO 6 are not brought out to the expansion header on a PiB Rev.2. How are you testing their value?

GPIO 2, 3, and 4 are connected to expansion header pins 3, 5, and 7 respectively.

How are you testing their value?

GPIO 2 and 3 have hard wired 1k8 pull-ups to 3V3. GPIO 4 has a weak internal pull-up to 3V3 enabled at power-up.

You can use http://abyz.me.uk/rpi/pigpio/faq.html#Have_I_fried_my_GPIO to check your GPIO.