Got an issue with my STTNG that has stumped me and stumped the repair tech I call in when I'm stumped. Long post...but I wanna give you all the details.

My drop target was not working well--wouldn't always drop when it should, and it turned out to have a piece broken off the reset assembly. I ordered a brand new, assembled drop target assembly from Pinball Life. I installed the assembly myself and, when I switched the game on, the right flippers engaged and blew F103. Figuring I might have done something wrong, I called in my expert.

He re-soldered all the connections, replaced the fuse, tested the solenoids, and replaced the 8-Driver Board with a new Rottendog board (in case I had blown transistors). Solenoids all test fine. Drop target up and down work. The switch functions as it should. The positioning of the target is flush with the playfield when down and doesn't catch.

Now, when starting a game, selecting Lock on ball launch locks the first ball. The target pops up as it should...but, when the next ball is auto-launched, the drop target tries to pop up a few more times, then drops. The next ball then locks. Repeat. Ball 3 locks. Multiball ensues.

Here's what we've tried so far:
* Checked the voltage on the UR 12 volt--just under 14 (about 13.6-13.9). I have a color DMD, but even with the DMD unplugged there's no significant change.

*Swapped the original 8-Driver Board back in. No effect. (I didn't blow transistors after all.)

* Checked all the optos. Found one trough opto out and replaced both trough opto boards with new ones. No effect (other than that all 7 trough switches now work).

* Fixed a sticky kicker in the Borg ship. No effect (other than that it doesn't stick anymore).

* For good measure, we even rebuilt the connectors at the bottom of the MPU board which showed some old acid damage (the MPU board itself was replaced with a Rottendog board with NVRAM).

The only other weird thing we've seen is that occasionally the Borg Lock opto (Switch 31) blinks in test when it shouldn't but it's infrequent, and wiggling the wires etc. doesn't trigger it. Tests fine when manually activated.

So, here we are. We're stumped. Any suggestions what to try next?

It doesn't seem to be a mechanical issue. Drop target up and down work fine in the solenoid test, and the switch is registering properly (solid in both open and closed) in the switch edge test. The down coil and switch on the drop target assembly are both brand new.

Here's precisely what happens:

* Game starts normally. I select Light Lock as launch bonus.

* Drop target gets a drop signal and goes down (or stays down if it's already down).

* Ball 1 launches and locks.

* Drop target goes up. (All good so far.)

* Ball is fed to the shooter lane.

* As the ball launches, the drop target "twitches" in place once (as if trying to raise again) then drops. The solenoid that drops the target then activates twice as if the target is trying to go down again.

* The second ball reaches the hole and locks.

* The drop target pops up.

* Sequence repeats. Third ball locks. Multiball.

What seems to be happening is that the drop target is getting a signal to drop the target again (multiple signals based on the multiple times the coil fires) when it shouldn't--as if it thinks lock is lit when it isn't.

All of the optos associated with ball lock have been replaced with new ones. There was a bad opto on the trough board, so I replaced those with new ones as well.

Not sure what to try next.

I tried that on the switch that was on the new assembly I installed. It tested fine and showed no phantom switching issues. Just to be safe, I replaced it and the diode with a new switch which also tests fine. The problem is still there.

The malfunction that prevents the game from playing properly is directly tied to the lock--both as described (when choosing Light Lock as the launch bonus) and when locking the ball during normal play. Once a ball has been locked--either in the Borg ship or in the more common fashion--Lock lights on its own as soon as the next ball is launched from the shooter, dropping the target as described.

I was testing other modes today as well and watching the behavior of the target. It always goes up when it needs to, but it pulses a few times when it gets to the up position (just as it pulses multiple times when the target drops).

bobukcat gave it a try. No false readings from any switches due to vibration.

Pin_Guy Lock is lighting as soon as the ball leaves the shooter lane switch (as the shooter fires it). Today as I was testing, I was getting a new symptom where, instead of the already-up drop target pulsed up as many as a half dozen times before dropping.

I kind of figured those two switches are the primary contributors to lock. Both of those switches test fine, and moving them, shaking them, etc. doesn't give me phantom readings in the edge test. Both of those switches are brand new--I replaced them both in the last week as part of my ongoing trouble shooting.

it's like the drop target up AND down are getting all kinds of crazy signals when Lock lights...and Lock is lighting for no apparent reason.

Pin_Guy, the next thing on my list of stuff to try is the switch matrix--I'm guessing that checking the switches and diodes in both Column 5 and Row 7 would be where to start. I do know the switch and diode on 68 are good (checked those), and the top drop target switch (57) and diode have been replaced with brand new ones. 58 has also been replaced recently--the lug that the playfield sits on when fully up was partially unscrewed when I first got the game, and that switch was getting repeatedly bashed. (That's rectified now.)

phishrace I actually did try a new ribbon cable and it didn't change anything. But I'm also going to check (and probably replace, for good measure) the IDC connector that goes to J4 on the 8-Driver since that's where drop up and drop down get power.

My game has a year-old Rottendog CPU board. The ASIC appears to be fine--no bent pins.

holminone The target isn't just falling on its own. It's falling as a result of the the drop target down solenoid knocking it down. In test, both up and down function normally, with zero problems. The height of the target is adjusted properly (flush with the playfield) and its not catching on the playfield as it goes up or down.

When you chose "Launch Probe" on ball launch, the target comes up and stays up, but there is other weirdness. It doesn't just pop up once...the up solenoid continues to fire repeatedly while the target is up until you fire the ball from the cannon, at which point it stays up and behaves normally.

There's something sending erroneous up and down signals to the drop target.

EDIT: Ah...I just re-read your second post. I was thrown off by the "blue solenoid" bit--mine's yellow. Yes...that's what's happening. The down-target solenoid is dropping the target.

Thanks for everyone's input. The problem is fixed! I documented the whole saga on my site: https://www.davesclassicarcade.com/tng-drop-target-saga

But, the TLDR version is that it turns out that the blade on the drop target switch on the replacement assembly I bought (as well as the one on I replaced that one with) was the culprit. On close examination over the weekend, I realized that the plate that pushes the drop target up was sometimes getting on top of the switch blade so that, when the plate dropped back down after pushing the target up, it was re-engaging the switch.

I compared the new switch to the one on the original assembly and the original blade was a good half inch longer than the one on the new switch--long enough to prevent that plate from getting past it! Replaced the blade on the new switch with the longer one from the old switch and the problem disappeared.

Thanks again for everyone working through this with me. It's insane that it was something so simple (yet hard to observe) at the heart of this three-week ordeal.

Pin_Guy Here's a pic of my original assembly. You can see how long the switch blade is here.

What was happening in my case was that the plate that pushes up the drop target was getting in front of the switch from time to time as it went up. It had just enough play to move sufficiently to drop down on the switch when it fell back down. I wish I had a pic of the new assembly as it was when I received it to confirm the length of the switch...but I'm certain it was shorter than this original. I'm also sure the clear plastic piece was right-side-up. I definitely would have noticed when soldering.

IMG_8213 (resized).jpg