Quoted from Djshakes:Having a couple issues. Sometimes when left Cannon is loaded ball completely jumps the wire form.
Things to check:
1: Make sure the play field slope isn't too steep and that it's level side to side.
2: Measure the coil resistance, this coil should be an AE-800 and measure 4.2 ohms (you never know if someone removed a few layers of windings or installed the wrong coil. I found one like this in my machine, the tech made it stronger by removing coil winding rather than fixing the actual problem
3: Check that the popper housing is tightly secured to the playfield
Quoted from Djshakes:I may have to pull subway and clean all the optos. However, all worked properly in single switch test.
Fortunately you wont have to do this, you can remove all three pairs of optos without removing the subway. If you think it would be easier, you can remove the entire subway wiring harness fairly easily, there is one coil connector and one switch connector; if you do this, the only spot you will have difficulty is the coil wires, probably easiest to just remove the coil brackets and pull the harness with the two coils attached.
Subway (resized).jpg
The ball search you describe shouldn't occur with just a failed/intermittent subway opto alone, as the ball should be seen by optos in the VUK that its fed to, the problem you are describing sounds more like a VUK opto problem. A good check to do is to remove all the balls from the game, with no balls installed, all 23 of the optical switches should read closed, if one doesn't its not working.
Another good check you can do for the VUK's is to load 4 balls, one at a time, into any of the subway holes while monitoring your switch edge test. Since the subway coils will be de-energised all the balls will lead to the Left lock, this VUK has four optos and you should see them sequentially close as the balls pass by the optos, then read open where each ball is sitting. So after loading all 4 balls, switches 35, 41, 42, and 43 should have all changed from closed to open.
A working STTNG matrix with no balls installed should look like image below, the light green switches may or may not be closed depending on the drop target position and the if the coin door is open, but you are primarily concerned with status of the optical switches in columns 3, 4, and 6.
STTNG Switch Matrix-no balls (resized).jpg