While playing last night, as the last of ball 2's multiballs drained the ball didn't end. Then, ball search.
All 4 balls were in the trough.

Poking around revealed many switches not registering. The entire switch matrix row 2 is out.
Tron Legacy-Switch Matrix-Pro, p49 (resized).PNG

A multimeter probing reveals nice continuity from the end of the line SW32 Bottom Bumper all the way up to J1P3 pin & the neighboring SMT reisstor on the CPU PCB, so no broken wiring to blame.
Tron Legacy-CPU Layout, p110 (resized).PNG

Probing a little further in, game power off, the measurements at the resistor test point, capacitor test point, & the closest leg of the transistor seem to match the same set of probed items on the Q1 row 1 set of components. So, assumption that R2, C2, & associated traces are OK.

Suspected culprit: Q2 transistor. Thankfully, it's thru-hole, so easy removal & replacement.
Tron Legacy Switch Matrix Transistor (resized).PNG
Is there a good way to test it, perhaps by probing J1P3 with logic probe? Should I be seeing ultrafast flickering at 5V on this pin? Or probe it & a neighboring pin & see if they resemble each other subjectively? My ancient multimeter probably won't be of any use here.

If Q2 is indeed the culprit, recommended to swap all of its neighbors when I swap Q2, under the assumption that they all might tend to go together based on being in a similar batch, similar usage, etc.? Or better to let these lie & address only as needed?

Thanks in advance for any help.

Yup. It was Q2. A new 2N3904 & all's well.

Edit: the good ol' logic probe pointed to the smoking gun. All 4 transistors were chattering on the top side, where they got their pulses from the little SMT chip above them. The 3 transistors on the 3 working rows were also chattering on the bottom side, where they fed into the head pins for the cable connector. Q2 was stuck high at 5V on the bottom side. Second time I've used my logic probe--what a great little tool.

Thank you, hoby1. Kind of you to post in my little "private" thread. :]

I figured I'd follow up for posterity & for the day when this happens to me again & I need to look it up.

Note to future self: $4.54 for 20 transistors = $0.227 to repair (wonder how many pennies I spent on solder & depreciation of my solder sucker?)
https://smile.amazon.com/gp/product/B008IFYEP6

Whoops, it happened again (sort of ).
All's not well in the grid on my Tron Pro.

1.
Last week, upon game start, the Recognizer bank continually went up & down. Suspected bad switches 52 (3-Bank Motor Down) and/or 53 (3-Bank Motor Up).
Further research revealed the 3 Recognizer 3-bank targets are also dead.

2.
Ah-ha! Must be 2N3904 transistor Q4 for switch matrix row 4, on pin J1-P5.
I'd had the same problem w/ row 2 in March 2017, fixed w/ a new transistor, so I still had 19 more transistors in stock.
See above.

3.
I replaced Q4, and the game behaves perfectly in switch self-test. The bank goes up & down & stops at the right spots just splendidly. The bank targets work. All other switches work. Pushing on other switches in the game, or bumping/shaking the cabinet & PF themselves do not register erroneous switch closures on the switches in row 4.

4.
BUUUTTTTT!!!!
Gameplay is wonky & irrational!!!
Watch this video: https://photos.app.goo.gl/E1Pek8rrDFVsDSxAA

a) 00m03s: When I push start a ball kicks into the shooter lane, it registers a hit on the Recognizer bank (insert glows & cool sound is played).
b) 00m16s: When I'm batting the ball around the PF or, in this case, when I think it's draining, it registers a ton of rapid-fire hits on the Recognizer targets & announces "Battle Rinzler for Disc War Multiball" & starts spinning up the identify disc.
c) 00m22s: When ball 2 starts, the disc is spinning & its 4 flashers are flashing, but the bank stays firmly up.

This behavior is very repeatable now that I fixed (or perhaps "fixed" row 4).

I can grasp some switch matrix (column?) or other shorting weirdness that would lead to erroneous phantom switch closures on the 3-bank target, but I don't know why the 3-bank isn't going down when it starts spinning the disc in preparation for Disc Multiball.

Help me. I don't want to stay stuck & have the Grid Bugs get me!

Thanks,
-Jason

Entered the grid last night to try to exterminate the grid bugs that are wonking up my recognizer & disc.

Found some interesting switch matrix behavior.
Does this sound like an issue w/ a switch diode, wiring, the switch matrix chip on the MPU, other?

There's some weird correlation between row 2 & row 4 of the switch matrix. If a switch in row 2 is closed, then the corresponding row 4 switch in the same column will also close. And vice versa.
Example: When Trough #4 at row 2 column 2 is closed, then Recognizer 3-Bank at row 4 column 2 is also closed.

This explains why my 3-bank was dropping instantly--the trough switches are in the same columns as the Recognizer 3-Bank switches & the 3-Bank Motor Up/Down switches.

In self-test, even the many unused switches in row 4 show as closed when their corresponding switches in row 2 are closed (Shooter Lane, Left Outlane, etc.). See attached 2.JPG (which shows 4 balls in trough, w/ 4 corresponding switches in row 2 also closed).
Exception #1: closing Trough Jam at row 2 column 6 does not make the unused switch #54 at row 4 column 6 close. I'm guessing because Trough Jam is an opto.
Exception #2: closing Left Ramp exit switch #37 at row 3 column 5 will also close switches #34, #35, & #36 (which are all on row 3).

Other observations:
- If the 3-bank is down & switch #52 is closed as it should be, all switches seem to behave except Trough 2 switch #20 (2 above on matrix) is stuck closed.
- If the 3-bank is up & switch #53 is closed as it should be, & if there is a ball closing Trough 2 switch #20, then switch #52 is also falsely closed, & the game thinks that the 3-bank up & the 3-bank switches are both closed, hence the odd bank behavior. See attached 1.JPG.

Phew!

Any help appreciated.
If not for me, then do it for my 6yo son, who's playing the heck out of my machines these days! :]

Thanks,
-Jason

1 (resized).JPG

2 (resized).JPG

The Grid (resized).JPG

Grid bug squashed!
Tron rebooted & operating nominally!

Not a loose switch.
Not a misaligned disc opto.
Not bad wiring.
Not a bad switch diode.

The.
Trough.
Opto.
PCB.

One of the consistent misbehaving switches (regardless of presence of balls in trough & regardless of 3-bank position) was that the Trough Jam switch was always closed.
Unplugging the trough opto PCB made everything else behave.
So, new trough opto Rx PCB from Pinball Life & all's well!

Thanks,
-Jason

Thanks, northvibe .

It was a bit of a puzzle, so I'm patting myself on the back for solving it.

As for attempting to repair the board itself, it hadn't even occurred to me. The replacement cost was low, so I didn't think to invest time in it.
I only went as far as wiggling the connector, which didn't help. *blush*

When I see surface mount stuff, I usually just shy away, even though yah, this PCB has several thru-hole components.

I kept the busted PCB & am happy to mail it out to anybody for free, rather than send it to the eWaste bin.

Thanks,
-Jason

Dear Past Jason,

This is Future Jason writing to tell you how awesome you are.

You'll never believe what happened a few nights ago! The wife takes the kids on a short trip, so PINBALL TIME!

During an awesome game (of course), when I earned another Quorra add-a-ball, Quorra didn't give me the ball.
Argh.

Testing revealed switch matrix row 2 was out.
Dang.

Welp, time to check out the manual on my computer.

Navigate to Google Drive\Games\Pinball\Tron Legacy, and...heeey, what's this folder named "Switch Matrix fix"?
It has some files from 4.5 years ago!

switch matrix fix-jasonbar is organized (resized).JPG

And it has a TXT file called "Tron switch matrix fix Pinside thread.txt"!
In that TXT file is a pinside thread URL.

Oh look!
This happened before!

I remember now!

Let's look in the pinball electronics box, in the board components bag...heeey, what's this baggie? It says:

PXL_20210813_045822793 (resized).jpg

Oh man, this will be cake!

Fixed!
(After a little confusion with wonky switch behavior b/c I forgot to trim the transistor legs after soldering, so they were shorting to the chassis plate, & any time a switch on row 2 closed, its entire column also closed--a problem that Distant Future Jason might make 4.5 years from now, so it's a good thing I'm writing it down here, even though it's wicked embarrassing...)

In summary, Past Jason, thank you for being so organized. You saved me lots of time & got my Tron back up & running rather quickly.
You're the greatest.

Sincerely,
Future Jason