Just checking, but did you repin the cables going to the rectifier board?

I didn't mean to sound like a di__, but in the past I was misguided in troubleshooting because I had assumed the person had changed out the connector and pins on both sides of the connection.

Like Frunch asked, what are the voltage readings? You should be seeing 43 volts on one side of the solenoids. Per Altek manual, a flashing Q19 means the associated coil is shorted or open. Since you don't have any coin door lights, and Q19 is the coin lockout relay, look at the connector for the coin door and make sure its good. I don't know what the Altek board would do if the lockout relay is disconnected. If disconnected, use a jumper to connect it, power on, and see if that takes care of Q19 flashing.

Let us know.

Use a meter to check the resistance of the coil - you will have to remove one side of the diode to get a good reading. While you have the meter in hand, and before checking the coil, measure the voltages per Frunch's request.

That’s good. We know the issue is not at the rectifier board.

Did you check the voltages at the coils? You should have around 43 volts.

It’s possible you have a connector issue on the Altek board. Do the connector pins to J4 and J3 look good?

Another thing to try is a jumper wire, one side connected to the ground braid at the bottom of the head, and briefly tap the metal tab on the components at the bottom of the SDB. A solenoid should activate with each one. I don’t have a schematic in front of me, if you have one, you can see which transistor is associated with which solenoid. If the solenoid doesn’t operate, then we can go down another path.

It sounds like the coil or the diode for the coin lockout relay is bad. Since this is home use, that should not be a problem leaving it disconnected.

It sounds like you have a connector issue - the usual suspect is J4 on the MPU. Reseat that and see whether that clears up the issues. Beyond that, I'm not sure where to go from here.