Does it take the coin? Code 50 will go away after the door is closed, and after the next coin is played. If it takes the coins but the code 50 doesn't disappear, check the door switch inside the hinge.
The hopper will run if the previous play was a win, and will run until it either finds coins or kicks a tilt code (time delay to produce a coin in the hopper exit).
If the hopper is running, put coins in it, and let the machine dispense coins until the hopper stops. If it still doesn't stop, check the hopper coin detect switch or connector behind the hopper assembly.
Pressing the test switch four times gives you a 00004 on the display and will dispense 10 coins to test the switch and hopper.