Allen, TX
Quoted from RebootMac:Hey guys,
So I acquired I bit of a beater High speed for the Barcade here in town, After giving up on the MPU and ordering a nice shiny new one from Rottendog I began to realize the Background sounds are always on. No matter what I put into settings such as attract sound or turning the pot on the inside of the cabinet the background buzz music sound is always there. Always on and always the same volume. The voice and sound are affected by the volume pot. But background is not. 12v out of the power supply and logic lines are testing clean. 4.99 on 5v outlet. My manual is missing the last quarter of pages I believe as the back cover is missing and I cannot find the background sound board schematic. If anyone has any clues or thoughts let me know!
Thanks!
You can grab a PDF of the manual on the IPDB page: https://www.ipdb.org/search.pl?any=high+speed&search=Search+Database&searchtype=quick#1176
That's odd that the background audio isn't affected by the volume pot. Just to make sure, you are talking about inside the cab, on the left? Don't want to assume someone hasn't FrankenWired™ the thing 
Unfortunately, I don't have anything concrete to give you on why it's happening, but folks like GRUMPY probably have some ideas.
Side note: The humming can be significantly diminished if you ensure all of the boards have screws in the appropriate spots. Used to be real apparent on mine, but now is barely noticeable.
Dunakeszi
