I'd check all the optos on the subway and anywhere else you find them. Your game doesn't know where some of the balls are.

LTG : )

Congratulations on acquiring such an iconic game!

I would check all of these in switch edge test to find out what optos (TX and RX) are fully working, and which ones are not. If you remove all the balls, you will know their status right away since every optical switch should read closed; if one or more show open, focus your efforts there.

If i remember correctly i had similar issues when i got the one i had. It turned out to be issues with the diverter coils, i believe one or both were locked on. Check pinballninja's website i believe he has a couple of fixes regarding this issues.

STTNG can be a funky beast. When i had similar issues, I got lucky that they went away after re-seating all the connectors on the boards and cables. If you havent already done that, it's a good thing to check. My issues started after a move, which likely caused somehing to work loose.

And do all the basic voltage checks at the test points on the power board. Search for how to do this. It only takes a few minutes once you know how to do it. It's common to have bad capacitors and bridge rectifiers. Low voltage on the circuit that supplies power to the opto switches can cause some strange problems.

Eject all the balls in the service menu. Then load 6 balls into the machine. If the machine loads the subway balls then it's not and opto issue. If it's seems to be an opto issue try ref lowing the solder joints on the trough opto board(transmitter most likely failure). For the cannons check the optos in switch test and make sure the home switches are adjusted properly.

I also had a fatigue failure on the 3 amp fuse that powers the optos. That was really tough to find because the fuse looked good in the circuit and out of the circuit. It wasn't until I just replaced the fuse that the final issues I had went away.

What Lloyd said.

For your cannon issue, the opto's in the cannon load are not reading the ball not being there. There are only a few things that could be causing this. Either the Rx or TX is dirty or needs to be replaced. There is a break in the cannon harness wires. There is an issue on the 16 opto PCB that is on the under side of the playfield. I would start by cleaning the the optos, then inspect the wiring to the optos, then do a continuity test from the optos to the wiring harness connector. If none of these fix your issue, you likely have an issue on the 16 opto PCB. The most common failure I have seen on this is the LM339. Before replacing the LM339 for this opto, check and make sure you don't have a connector issue on that board.

Since you seem to have a multitude of optical issues, can you post a picture of the switch edge test display with all the balls removed so that we can see what optos, appear to be working?

It seems Column 3, which all are optos, is completely missing.

Could be a CPU board problem, reseat the J207 connector and check the Green-Orange wire at J207:3.

Also there seem to be a problem with the Left return lane Eddy sensor, it is stuck closed. Though this is probably unrelated to your opto problems.

Also reseat J5 on the 16 opto board, the green/orange wire from the CPU board goes to pin 10 of this connector.

The CPU board is in the lower right corner of the backbox, J207 will be on the bottom of the board and is clearly labeled.
MPU J207 (resized).jpg

More than likely you can adjust this to get it working, just turn the alignment potentiometer until the LED on the eddy board turns off.
Eddy (resized).jpg

In a nut shell it is able to sense when a metal object passes in close proximity to it. Williams used these for both inlanes in STTNG. The LED on this module should be off, and then light when it senses the ball.

Great you're getting some progress, though J206 and J207 are compatible and carry exactly the same pins, but perhaps there's a dodgy contact with J206.

And also, you'll find the Backbox Board layout on page 2-2 in the STTNG manual. If you haven't already - armed your self - with this manual, its' available here:

http://mirror2.ipdb.org/files/2357/Williams_1993_Star_Trek_The_Next_Generation_Operations_Manual_with_OCR.pdf

Since this is your very first DMD game, you may not fully understand what you are looking at on the switch edge test screen. The image on your DMD is showing you what the status of your switch matrix is. Every switch is represented by a single dot, and every switch that reads as closed, is shown as a square with a dark dot. By comparing this image with the Switch matrix from your game manual, and knowing that all optical switches should read closed unless blocked, we were able to determine the column 3 failure.

Attached is what your switch matrix will normally look like after ejecting all the balls. Note, Top Drop Target switch 57 may or may not be closed depending on it's switch position; it should read closed if in the down position.

STTNG Switch Matrix-no balls (resized).jpg

Also please note that column 9 will not show up on your edge test screen, you must test these switches under the cannon test menu if you suspect a problem.

To find out in what direction to search, you can perform a simple test on the CPU-board to check if column 3 is still working here.
If this test triggers switch #31, the problem has to be found in harness or the opto-board below playfield.

-Go into switch test T.1
-keep coindoor open, (no hi-power needed for coils now).
-unplug J206, J207, J208, J209, J212
-make a connection between J212-3 and J212-4, for example with a small screwdriver.

Does that trigger switch #31 (on release) ?

picture:
cpu #31 J212-3+4.jpg

Can you plug into J206 or J207 then? Mine was plugged into J206. I thought maybe that was my problem with my 5 switches, but I tried J207 and no change. Is one correct?

0B25226B-D033-4D6B-8734-6C29345CD804 (resized).jpeg

It doesn't matter which you use, J206 and J207 are connected to each other, see the WPC Schematic Manual, the CPU-page, or you can even see the traces on the board going straight between those two connectors. It's the same with J208 and J209.