Something a bit different from the usual arcade repairs, recently I picked up a Street Fighter 2 pinball machine (my first pin). It was a wild ride fixing up that, but that's a writeup for another day. As the title states, the big problem at hand was that the table was not putting out any valid sound, there was buzzing but none of Guile's theme or whatnot.
So in Street Fighter 2, it utilized the Gottlieb System 3 boardset. This utilized two different sound boards, a large main sound board and a smaller auxiliary sound board. The main board was the one running the show, while the auxiliary sound board handled samples (such as voice I think). The main board itself can even be split up into two different sections, a Y section and a D section, each have their own RAM and ROM. Unfortunately I am not all to familiar with the inner workings here, I just know that one section does the talking with the Aux board and one just makes sound.
On to the troubleshooting! One thing to note is that when these boards boot up, they both make a beep noise to signify that both boards booted. They also each have LEDs to signal that they are both operating properly. In it's initial state, I would only hear one beep, meaning that not everything booted. I also noticed that the mainboard LED was stuck on and the aux board LED was stuck off. When I would start the game, it would just buzz at me, sounding like it was just resetting. The buzzing was also a good indicator that the sound amp was working, because otherwise I wouldn't hear anything out of the speakers. The way I attacked this issue was by running through Marco from Pinside's test ROMs. These are excellent tools for troubleshooting System 3 boardsets and were critical to fixing this. The test was always getting hung up during the RAM test for the Y section of the main sound board. After replacing it (it was just a 6116 RAM), both sound boards fired right up and I was hearing the game!
Now the game is running and has been a blast! Sorry there wasn't as much explanation with this repair, truth is that I don't really know a lot about these because I didn't have to deep dive into it, the test ROMs did all the work for me. There is an EXCELLENT video on how to use the test ROMs, I linked it to the bottom if you want to see the process in action. Funny enough, it was the same failed chip in the video as what I experienced.
Cool video on how to use the test program: