I've got an old ( 5yrs) pair of recently obtained ATC SCM7 speakers.
Something sounded wrong from the off, and I think I've isolated it as a
faulty tweeter. One is distinctly louder than the other, and I can't
reliably differentiate the LF units, which seem much the same.

I've reached this conclusion by just connecting up the HF or LF
connectors on the speaker terminal panel. Swapped across
channels/sources/amps to rule out other issues.

Anyway, and assuming this test is reasonable, what might the problem
most likely be? Tweeter or crossover? And sourcing ATC units? Anything
like the Dynaudio closed shop of recent experience? I will contact them
at some point . . .

And another thing. I was doing some testing using a Windows XP laptop as
source - useful as I can use the software balance control in the native
sound mixer app. But how are you supposed to centre it? Seems very easy
to have it a click or two off centre.

Rob