Volume control problem - Rio de Carnival pachislo

[EenieQWolverine]

I just acquired a 2005 Rio De Carnival pachislo with very low volume.
It does not have any volume potentiometers placed into the speaker wiring.
On a circuit board next to a 'Time Button', there is a 'Sound Button' that when pressed makes a short tone and then stops.
I can find no way to adjust the volume.
I have had plenty of machines that were too loud, but this is a new issue to me and any advice would be greatly appreciated.

[Wayne-Ooo]

6302_Super_Blackjack_Buttons_1.jpg

[EenieQWolverine]

Thanks!!! It couldn't be easier once you know the procedure. Thanks for saving me hours of aggravation!