I have an unusual problem with my Star Trip - the sounds work correctly as far as I can tell but about 1 minute after powering on whether I start a game or not, there is a whine that kicks in. See the quick video I made, a little after a minute you can hear it.

The Star Trip used the SSU-1 so there is some logic on the MPU board but since the sounds appear to be happening at the right times I am at a loss. I figured before I start randomly replacing things on the sound board I would post and see if someone had any ideas.

https://photos.smugmug.com/PublicPics/i-fnwbFg8/0/8a0605c1/640/StarTripSoundProblems-640.mp4

Fortunately I was able to fix the problem.

For future searchers, the Star Trip uses the SSU-1 sound board. It is driven by 4 transistors on the solenoid board. I had thought my sound was working correctly but in listening to a couple of YouTube videos of gameplay, I could tell my sound wasn't all there. The self-test for the solenoids also runs the sound test and with it I was able to identify that chime "C" was not working. Using Viperrwk's amazing research I was able to identify the specific transistor.

I wasn't sure if that was the whole problem but it looked like it needed to be replaced anyway, so I replaced it on the board and all my sound problems (both the missing sounds and the weird buzz) went away!

https://pinside.com/pinball/forum/topic/game-plan-mpu-repair-a-shotgun-guide-w-pix/page/2#post-2050904