Hope everyone is staying well and have taken the opportunity to get vaccinated when they can. One of the most asked questions we get is Why do my coils activate out of sequence in self-test and game play or some activate several times and others don't. Let me first go through the schematic side of this question.
There are 8 signal lines that come off the J4 connector on the MPU board. Four of the lines are binary address outputs for the momentary solenoids and operate solenoids 1-14 and 16. The other four signal lines are for the continuous solenoids 15, 17-19, and are just individual outputs.
MPU Board Schematic:
Solenoid Driver Board Schematic:
J4 MPU Connector Pins:
Let’s say you want to fire Solenoid Q5. In binary that would be 0101 as you can see in the chart above. That means J4 pins 1 and 3 would need to be high and pins 2 and 4 would need to be low. Now think what would happen if one of those lines was not making a good connection because of a dirty pin or a broken wire. Using the same solenoid #5 example, let’s assume pin 2 has a broken wire. The MPU board thinks it is sending a command to turn on Solenoid #5, but the SDB is getting 0111. You might be asking if the wire is broken why is Pin 2 high. The pins are tied high on the SDB so the solenoid circuit will take this as a high because it can’t be held low. And that means solenoid Q7 will pop instead of Q5.
One other thing about this - lots of times I will have customers say they have done a continuity test on the pins, and everything looks good. Two things with that, one is shoving a probe into the connector is not a good test. This might help make the connection and the other thing is having continuity doesn't mean the wire can handle current. There might be just one strand of wire connected to the pin in the connector which will show continuity but will never be able to handle current. So just replacing the pins in these connectors sometimes just needs to be done so you know things are right.
The last thing to mention is the continuous solenoids, Q15, Q17-19. Q15 is the Flipper Relay and Q19 is the Coin lockout. Q17 and 18 will be different on all games and sometimes not even used. And again, you can see how a broken wire will cause them to be on.