Working on a machine, customer replaced the speakers with some car speakers he had in his garage. After replacement he smelt burning, and noticed the bottom segments of players 3 & 4 weren't working.

After looking over the display board (D-11610) I couldn't find anything that seemed ruined. I then started testing the components and everything seemed to be ok on the display board - R14 tested within tolerances of a 10K resistor, U15 was putting out anywhere between -19 and -80 volts on each output pin per spec. Wiggled the jumper, nothing seemed to be wrong.

In frustration, I started looking over the board for anything obvious, and I found Q77 looked burnt at one of it's legs. Tracing it back, it looks like it goes back to a solenoid. So it seems unrelated.

Planning on replacing Q77, but I don't know how a set of speakers could lead to all of this, or what my next steps should be beyond replacing Q77. Needing some guidance here.

You guys were right, the Q77 wasn't toasted, it looks like whoever replaced it, didn't clean the board very well when they replaced it. So I cleaned it up.

And before I go into this, the display board is a D-11610, it's not the board schematic listed in the F-14 Tomcat Manual over at Internet Pinball Machine Database - Look up the Space Station machine for the display specific schematic.

After looking at the display board some more, I found a trace that was nearly burned apart, after re-attaching, has fixed nearly 90% of the problem. The top displays (players 1 & 2) are functional again. I didn't mention it but they were illegible and segments weren't even lighting up in entirety. But that has been fixed.

Still having issues with players 3 & 4, but what I've come to realize, it only happens in the first few minutes of operation. Eventually, the lower segments on players 3 & 4 will eventually stay lit consistently. I shot video of the behavior, when it does happen, it seems to only happen when player 3 is lit up, then players 3 & 4 bottom segments go out. Starting to suspect U9 (4050) may be the culprit. Maybe after some use it starts working. I can reflow as a first troubleshooting step, just wondering if I need to go ahead and replace it.

Video of the behavior:

Got it fixed. I went ahead and replaced U9 (4050 hex buffer) on a whim thinking it was needing time to warm up and was wearing out. After replacement, it started working perfectly.