I did a pin repair housecall on a T2 the other day. The board had extensive trace damage from leaky batteries. No problem to repair that.

The machine still had some issues. Row 1 ground short, and two balls would shoot into the shooter lane.

The ground short was easy. SOmehow the slam tilt was shorting against the lock mechanism. Bent that back into shape.

I pull out the balls from the trough. I got four of them in my hand. I look down at the sticker for how many balls are supposed to be in the machine. I ask the owner to come over. I ask him how many balls do I have in my hand. He responds, A man isn't supposed to ask another man that question. We had a laugh. I showed him the sticker. Ball problem solved. Three installed back into machine.
He had no idea how an extra ball got there or how long it had been that way. He said he had machine for 20 years.

I looked at all the switches in the row. Machine told me switch in that row was shorted to ground ( just not which switch). I just started at first switch. Slam tilt. Saw it was bent out and resting on lock mech. As soon as i pulled it away, The ground short went away in the switch test... I then knew it was x marked the spot. LOL.
Usually problems are not that easy. The board was a bitch to repair though. I think 7 or 8 traces damaged by acid.