Not supposed to do it randomly. Only when a ball is kicked in to the battlefield. And then only when beam broken.

You have an issue somewhere check the wires under the battlefield are not pinched or frayed or shorting to eachother or ground.

Then check coil diodes and clean and test your flipper optos.

How it's supposed to behave 3:20 into vid.

Plunger doesn't fire randomly. And never should.
I would suspect a flaky (but partially working)opto on the battlefield.
You will never be able to tell during switch test.
As testing that way won't show vibration and voltage fluctuations that happen during gameplay. Because of other coils fireing, lamps, flashers etc.

Good luck.

If it does it with another PCB. 100% you have a short or more likely break in your wireing. Somewhere.

Check the insulation where the wires touch the battlefield. And any stray wires not tied into the harness that might be broken internally if flexed or vibrated and can't be visibly seen. (Like stray ones in pic)

I had that on my shadow causing some battlefield targets to work intermittent

Check all the opto control boards and optos (every opto in the machine) one bad opto can mess the whole switch matrix. Don't forget the sanctum opto. Check for bad connections or solider blobs as well. Or cold solider joints.

Check the coindoor interface board for solider blobs or cold solider.

And if you haven't already. Visibly inspect the wires coming off the battlefield coil. And DMM test or replace the diode on it. And if it was done before, is it on the right direction?

It's not as hard as it seems. Just a little time and patience and you will sort it out.

Good luck.
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