BGW 750B early, middle or late?

[kb2umj]

First post here:

Is there a way of telling when a 750B output module was made? I'd like to get a clue as to when mine was made. I'm an owner of a 750B that has a buzz. Scoped the output and found a 60mv .1ms wide negative pulse every 8ms or so on both channels. Shunting the inputs drops it to <5mv. Just guessing, and that's all....... does anyone think it could come from the led vu circuit?

Is there any way of getting a schematic after finding out the "rev"?

Thanks in advance.

Michael