What usually happens is the respective "base" transistor leg in the transistor array (U3) goes open circuit which ultimately causes the final output transistor (Q9 here) to lock on.

Check the voltage at the base pin 3 of U3. If it's over 0.9 volts, U3 is suspect. When the base leg goes open circuit it usually reads near 5 volts which is bad.

What do you mean by "mV" reading? If you mean you're not getting a reading, an open circuit (bad solder/trace) to pin 8 will cause the same fault as above with Q10 (D.T #5) locking on.

BTW you can still get CA3081 devices on ebay, eg:
ebay.com link: itm

Probably time to go right through the solenoid driver board. Test all the driver transistors, diodes and CA3081 devices with your multi-meter. And look for any fractured solder joints around the pin headers that need to be touched up. Check the diode on the saucer (eject pocket) coil too - make sure the diode lead hasn't broken.

Check the solder connections on capacitor C26 because it might not be filtering the DC input properly. If you have an ESR meter, test the capacitor (after you've discharged it) and/or replace it.
Stern spec is 175 volts.
Ballys I set to 180-182 volts.

Stern displays can sometimes internally arc that reduces when you turn down the voltage. And some Stern displays gas out where turning down the voltage causes segments not to illuminate. So sometimes you have to compromise on the voltage.

Since you have working boards compare to those.
But most likely they're goners including the three transistors.

Are you getting diode readings across the three transistors like those from a working board?

What voltage are you measuring across resistor R55?
What voltages do you measure on each leg of R51?

Grab your oscilloscope. Be sure to set the probe to X10
Post a snapshot at TP2

BTW the centre leg of the trimmer pot looks awfully close to one of the other legs. Not sure if it' the angle of the pictures.

You only need J3 connected. The other connectors are solenoid related.

Resistor R55 sits across the base/emitter legs of transistor Q23. I'm kinda surprised the Q23 transistor isn't damaged with 4.6V across those legs. Can you adjust the output voltage on TP2 in a respectable range?

I just looked back at the thread and actually the first picture in post #16 shows the copper through hole VIA is missing at that capacitor leads solder pad hole.
Lucky Rikoshay got you to recheck the joint.

Hi Mark