Update:
@nem mentioned that there was a pot on the original arcade cab that controlled the volume itself. I verified this on the test screen and it confirmed that the master volume is at 0.
View: https://youtu.be/nxNMKwvo3qk
Looks like I will need another pcb. Will update as soon as I receive one and confirm that is the issue.
I had the same problem with my setup and I was able to find a solution but it is very strange and requires you to sacrifice player 1 controls.
With the system set up and turned on, music will play if you hold left on player one joystick. It sounds strange but for my setup, with the P1 joystick constantly held to the left, the music will/would play. If you bridge the Back button with GND you can hear the music like usual.
2 problems arise from this though. If you try to go into the game audits menu or volume control menu it makes a strange sound like a constant skipping record of the boss battle music and it's loud. This and the fact you cant make any changes to the game (unless you disconnect those 2 pins first).
The second problem (more obvious one) is that you can't use player one.
If you press the start button, the ships will be constantly revolving. Because the back button needs to be held for music your ships with be in an infinite look of rotation and even if you start the game, your ship stays at the left side of the screen.
On the plus side. If you don't press the start button for player 1 and you keep the P1 joystick button grounded to left/back, you can play the game with music and the other 3 remaining ships. Not a total loss or 100% win but at least it will let you enjoy the game.
Hope that helps.
