Angry Birds uses a solenoid to shoot the ball at the screen, if after coining the game up the computer does not see the ball hit the screen after a predetermined amount of time the game will display an error stating that the ball did not reach the screen.
The shooter mechanism is comprised of 3 main components a optic which tells the game the ball has been loaded in the shooter, an optic that reads the position of the plunger handle, and a solenoid to fire the ball.
The ball loaded optic is an infrared optic located in the bottom of the ball cup. The computer uses this optic for 2 functions 1st to stop the elevator from bringing balls up to the shooter if one is loaded and 2nd to tell that there is a ball ready to be fired, if this optic is not blocked the solenoid will not fire. The optic is a 12vdc device, at the four pin connector the orange wire is +12vdc, the black wire is ground, and the grey/orange wire will be 12vdc when the optic is clear and 0vdc when the optic is blocked (referenced to ground). (Please note early games used a micro switch in this position)
The plunger sensor reads the input from the customer pulling the handle back to tell the solenoid that it is time to fire the ball. The plunger sensor has a 3 pin connector the orange wire will be +12vdc, the black wire will ground, and the grey/violet wire is the signal line which will be 5vdc when the sensor is open and 0vdc when the sensor is blocked (when referenced to ground). The sensor signal line must go below 1vdc for the CPU to recognize the change!
The solenoid which fires the ball is powered by a solenoid firing board (ICE part number AB2010X) which outputs 90vdc to the solenoid to launch the ball. A good solenoid will approximately read 3.8-4.0 ohms and that can be read between the purple and black wires. The duration the firing board is active is very short so you will not be able to read the output voltage using a multi meter.
Please see the document below for further information regarding the firing board and methods of testing the shooter mechanism.