I worked on a Berzerk last weekend that put out only three beeps, but the problem turned out _not_ to be the BSC but a bad RAM on the VFB board.
Do you see anything on the screen when it boots ? The machine I worked on showed 2 screens of garbage and then one screen with figures that represent RAM chips.
All of the chips were "black" inside except for one which was indicated "white".
The manual says that these are the RAMS on the VFB board. You will have to turn the image on the screen COUNTERclockwise 90 degrees "in your mind" to see what RAM is failing.
In my case, the on-screen one was top-right, so in reality it was the top-left chip on the board. Replaced that one with a known working RAM from another VFB board and presto: 8 beeps and a fully running game !
Lesson learned: 3 beeps doesn't always mean that the BSC is the cause....