John, it may be the fuse. Check it before you spend a lot of money and time.
From the SWR owner's manual:
The tweeter protection circuit for SWR Professional Series speaker enclosures includes a size 3AG, 3 amp, 250 volt, fast-blo fuse. Do not replace this with a fuse of a higher rating as it will void your warranty. A sudden burst of feedback or a heavily clipped waveform can cause the fuse to open, resulting in loss of output from the tweeter.
