Updating your Pi

source

sudo apt-get update sudo apt-get upgrade sudo apt-get dist-upgrade sudo apt-get install raspberrypi-ui-mods

HDMI not working

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The Pi outputs a relatively weak HDMI signal. Some devices may not immediately notice the Pi's HDMI or may not do the negotiation. Setting the hdmi_force_hotplug=1 makes sure the Pi believes the monitor/TV is really there. You might also need to set config_hdmi_boost=4 or even higher (up to 9) if your display needs a stronger signal. If the display is a computer monitor, use hdmi_group=1 and if it is an older TV, try hdmi_group=2. Do not set hdmi_safe=1 as that overrides many of the previous options. Using a shorter or better quality HDMI cable might help. Make sure your Pi's power supply delivers 1A and not 500mA. If you see a problem with the red colour - either absent, or interference - then try a boost. However it might simply be that the display requires a stronger signal than the Pi can give.

Reset root passwd

In cmdline.txt, add the following at the end of the line: init=/bin/sh

Reboot.

passwd pi

Reboot. Remove the previously added part in cmdline.txt (i.e., revert to the original).

Reboot once again.

I2C

http://www.raspberrypi-spy.co.uk/2014/11/enabling-the-i2c-interface-on-the-raspberry-pi/

http://www.raspberrypi-spy.co.uk/2013/07/how-to-use-a-mcp23017-i2c-port-expander-with-the-raspberry-pi-part-1/

Troubleshooting

First stop for help: http://elinux.org/R-Pi_Troubleshooting