Quoted from wayout440:

I would go to the 7408 and gates before the coil drives and compare the signals at the inputs and outputs between a known good coil drive circuit and the bad one. You can use a logic probe, oscilloscope, or DMM to do this. Most of the time I just use a DMM set to DC volts. Put the game is test mode, and jot down the results while probing the signals, noting the states of the inputs and outputs at rest and look for the changes or spikes of a pulse to determine logic highs and lows. Once I know what is going on there, I could find out which direction th head next.
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Quoted from wayout440:

Just look for the pulses. Put in coil test, set your probes up to monitor a pin on a known good solenoid channel so you know what you are looking for, then move the probe to an equivalent pin on a defective channel to see what happens there when the MPU calls for that solenoid to be activated.

Quoted from wayout440:

Your voltmeter or digital multimeter doesn't have probes?....I don't understand.
SCR.s are for lamp circuits and transistors are for coil circuits. Fundamentally they are both used as switches in pinball, but the circuits have differences.
But you do understand the concept of divide and conquer troubleshhoting. If you are testing a device between the logic section and the drive circuit and the signal is not present, we look upstream into the "higher" logic. If the signals we desire are present, then we look downstream to examine the drive circuit.

Quoted from wayout440:

I would go to the 7408 and gates before the coil drives and compare the signals at the inputs and outputs between a known good coil drive circuit and the bad one. You can use a logic probe, oscilloscope, or DMM to do this. Most of the time I just use a DMM set to DC volts. Put the game is test mode, and jot down the results while probing the signals, noting the states of the inputs and outputs at rest and look for the changes or spikes of a pulse to determine logic highs and lows. Once I know what is going on there, I could find out which direction th head next.
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Quoted from frunch:

I think it's the other way around--inputs are at 12+13, output is at 11. Wayout can set the record straight for sure though.
If I'm not mistaken, the blanking signal holds one input 'high' (pin 13) while the other input (pin 12) gets switched 'high' from another chip, leading to a 'high' output (pin 11) from the 7408...