This is from the website link I gave you above:
Coins Won't pay out (flashing 0 on the right Digit of the Meter Display):
1. Check to make sure that there are no coins jammed in the coin disk of the hopper and that the disk can be rotated freely about 1/8 of an inch (or more). The electronics to control the hopper are located on the interface board and will require repairs. The hopper also has a circuit board. Rarely, this board goes bad. If the hopper won't run, you get a flashing zero on the display along with the tilt light. The flashing zero meaning that zero coins were paid. This problem could be related to bad connections on the plug and jack assemblies on the hopper or the reel mechanism. To restart payout, press the hopper reset button and close the door (activating the switch on the top hinge of the door). After 3-4 seconds, the hopper should activate. See the above paragraph for clearing the tilt and restarting the payout! Also, see 'Battery Issues' to disable the tilt code retention.
Clearing the flashing Zero on the Right Digit of the display:
If the hopper runs, then pressing the hopper reset button and closing the door (activating the switch connected to the top hinge), should clear the flashing zero and allow the hopper to run. If the flashing zero stops for a few seconds, then comes back, it's because the hopper won't run or the hopper switch is failing to signal the coins going out. Also, see 'Battery Issues' to disable the tilt code retention.
Continuity test for the coin out switch of the hopper:
Testing for continuity using an ohm meter. 0 volts is either the negative end of the battery or the black with red trace wire on the coin in switch (easy to get to). The 'coin out' input resistor on the 'slot controller' board is R10. With the machine off, if you are measuring the resistance between 0volts and the end of the resistor that goes to the edge connector (circuit board gold pins), the resistance should go low (about 1 to 100 ohms) when the coin out switch is activated. If the resistance goes low, you have good continuity in the machine harness and connectors and the problem is the slot controller board. If the resistance does not go low, you have a problem with connections in the system (usually the rear connectors of the reel assembly).
Testing with a volt meter (power on):
R10 should have about 3.5 to 4.0 volts on it with the coin out switch open (either end of the resistor). If the resistor has 5 volts, the opto coupler (ILQ-74) is shorted and will need replacing.