Quoted from Manny65:If the ball search doesn't kick the ball out, then I'd say that the VUK is not firing to kick the ball up to the cannon. Go into Solenoid Test and check that the VUK coils work. Also the optos under the PF quite often have issues (eg cold solder joints) however the ball search would typically find the missing ball if this were the issue - worthwhile going into switch test mode and verify all your switches especially in the trough, VUKs and subway all work.
Quoted from oradke:Check (or better replace) the optos in the cannon and all the wiring. The wires in the cannon are a well known weak point of STTNG.
Quoted from bobukcat:When this happens is there a ball in the VUK to be kicked out to the cannon in question?
Quoted from Redwizard000:My machine does the same thing sometimes. The left hand cannon won't load, usually after locking a Borg multiball ball.
My problem is a cracked coil that runs a diverter under the play field. Balls get stuck there sometimes and the machine gets a little confused and starts behaving erratically (I think the computer attempts to compensate for stuff like that, hence the odd behavior?). You could check for something like that as well. While my cracked coil certainly does need to be replaced (time pending...) It does *mostly* work.
Quoted from Pin_Guy:Congratulation captain!
Sounds like an opto issue, very common in a 25+ year old game and can be caused by bad solder joints, wire connections, or failed parts. Some simple diagnostics will be needed to figure out what's going on. The simplest thing is to remove all the balls from the game and take a snapshot of you switch test screen , all 23 optos in the game should read as closed, if they don't you need to fix whatever ones don't before looking at anything else.
In the image below all highlighted switches in columns 3, 4, and 6 are optos and should read as closed switches. SW24 is a diode on the coin door interface that acts as test switch and should always read as closed.
[quoted image]
Thank you all for the suggestions! It helped me find the issue 
All of the opto's are working correctly and cleaned it all to be sure.
Coils and diverters are also working correctly.
So was pulling my hair out as I just couldn't find the cause.
But today, I was able to go into the service menu in time, just after the issue happened again.
I checked the Switch Test and I saw "Under R. Gun Sw.2" was closed and "Under R. Gun Sw.1" was open, that was strange.
So I assume the balls are getting stuck in the Through below the right cannon/gun!
And it was indeed so when I lifted the playfield, there were two balls in that through (popper bracket A-17887).
There is a metal plate inside that through, just before the plunger, where the ball will hang if the ball doesn't have enough speed to go to the plunger.
I'm not sure how to fix this, as the inside is really hard to reach:
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Do I need to replace the through or is there maybe an easier solution?
xingothx Awesome project!!!
Utrecht
Sanford, NC
