Quoted from Pin_Guy:

Sounds like a staging problem. Remove the glass and then REMOVE all of the balls from the machine, make sure you have 6; with the coin door open go into switch edge test, then drop 1 ball into each of the three VUKs and make sure they all reported in switch edge. Put the remaining 3 in the trough, again make sure they are all reporting correctly. Your switch edge test should show switched 36, 37, 41, 64, 65, and 66 OPEN; if not fix it so it does.
If the matrix looks correct, exit test and close the door; you should be able to start a game without it trying to stage balls.

Quoted from dsuperbee:

One of your diverter coils isnt firing. The transistor and or predrive transistor in the extra drive board burnt up, most likely because your tie back back wire broke off. Search the group. Very common issue, and tons of info on it.

Quoted from dsuperbee:

One of your diverter coils isnt firing. The transistor and or predrive transistor in the extra drive board burnt up, most likely because your tie back back wire broke off. Search the group. Very common issue, and tons of info on it.

Quoted from dsuperbee:

It won't fire at all. Check the latest in that was posted. Sorry I couldn't respond faster. 1st day of school from home. Juggling a 5 year old on zoom, his 3 year old brother and this

Quoted from dsuperbee:

It won't fire at all. Check the latest in that was posted. Sorry I couldn't respond faster. 1st day of school from home. Juggling a 5 year old on zoom, his 3 year old brother and this

Quoted from dsuperbee:

If they all fire then its a switch, or the diverter arm needs adjustment.
Raise playfield, and do coil test. You will see if the arm needs work.

Quoted from bobukcat:

So if you take all the balls out of the game, drop one down each vuk output, put three in the trough then turn on the game what does it do?

Quoted from Pin_Guy:

awww shucks

Quoted from Pin_Guy:

I never said to do that.
I said to do this:

VUKs are Vertical Up Kickers; these are the mechanisms the balls come out of on top of the playfield...I wanted you to drop the balls in those
Please visit the STTNG owners forum https://pinside.com/pinball/forum/forum/clubs-members-only ... you can find lots of information on ball staging issue there.

Quoted from Pin_Guy:

Sounds like a staging problem. Remove the glass and then REMOVE all of the balls from the machine, make sure you have 6; with the coin door open go into switch edge test, then drop 1 ball into each of the three VUKs and make sure they all reported in switch edge. Put the remaining 3 in the trough, again make sure they are all reporting correctly. Your switch edge test should show switched 36, 37, 41, 64, 65, and 66 OPEN; if not fix it so it does.
If the matrix looks correct, exit test and close the door; you should be able to start a game without it trying to stage balls.

Quoted from bobukcat:

And they open and close properly when I ball is placed in them / rolled through them? None of them are stuck closed or open?

Quoted from slochar:

What about the trough switches - are they are registering correctly. The logic in the game looks at the # of balls there and regardless of what it sees or doesn't see in the VUKs it tries to load them. For instance, you have the VUKs all loaded fine, but if the game thinks there's more than 3 balls in the trough, it's going to launch and fire one up for staging, causing an additional ball to be removed from a vuk, starting the same cycle all over again.

Quoted from Pin_Guy:

If you wouldn't mind, can you remove all of the balls and post a picture of the switch matrix with all of the balls removed from the game?

Quoted from drinkduffbeers:

I’ve currently got the exact same symptoms . On investigation looks like an easy fix for me as found the diverter arm had sheared
[quoted image][quoted image]

Quoted from donjagra:

If it launches a fourth ball before releasing one from the vuk, then you know it's your trough opto boards.
Do you still have the original trough boards? Those things are crap, best sttng mod you can do is replace the transmitter board.

Quoted from Tallon:

Did you check the stack opto in each VUK to see if one was out. That would cause the game to continually clear the VUK and then launch a new ball to reload then it read 4 balls in the trough?

Quoted from DumbAss:

I have some boards that can help you with the differential diagnosis if you think it's an electrical problem (i.e. not a mechanical problem with your diverters or engagement of the diverters).
These boards isolate the optos in your machine by using the optos on the test board. It will exercise your 16-opto board switch state logic detection.
[quoted image]
I also have boards that will help test your optos in the machine. The three small boards work together to provide indicators that the optos in your machine are actually working independently from the 16-opto board switch state logic detection.
Also shown at the top left is a complete replacement board that incorporates the indicators.
[quoted image]
If you're interested you can PM me. I don't know if they will definitively give you an answer because I don't know what's causing your problem but the information gathered may help you in one direction or another.
The post @ https://pinside.com/pinball/forum/topic/dumbass-test-and-reproduction-pcbs/page/4#post-5858635 will give you more details on their use if you're interested in more information.