Quoted from StratDoc:
How do you know what the correct voltages should be at the different pins and locations?
The part of the Solenoid Driver schematic I've highlighted above is essentially replicated for all solenoids.
See the below diagram for indicative voltages when the machine is powered on and idle.
The banded side of diode CR14 (right leg shown in the diagram below) where you measured 1.28V is connected to the "base" pin of transistor Q14. Consider transistors base pin like an input pin.
When the game is idle, the base pin of those Q driver transistors should have near zero volts meaning they're switched off resulting in their solenoids not being activated.
When those Q driver transistors have around 1.2V on the base pin, that switches them on and activates the respective solenoid.
None of the Q driver transistors driving momentary solenoids should have a constant 1.2V on the base pin.
Momentary solenoids are selected to activate for only a very brief time - typically 0.3 - 0.4 seconds.
Q driver transistors driving Continuous coils on the other hand can and do have constant 1.2V on the base pin when they switch on things like flipper enable relays, coin lockout coils, playfield gates, etc. The specific Q transistors wired for continuous coils are Q15, Q17, Q18 and Q19 which are listed on the top right of the SDB schematic.