Swapping the tweeters, between cabinets, will tell you if
it's the crossover. Applying a full range signal to a
tweeter(even at low volume), without the crossover blocking
mids and lows, greatly increases the chances of damaging a
working driver. If only the tweeter is not functioning;
it's obviously not the amp. If you find that the tweeter is
working; the components to look for and inspect(in the
crossover) should be a Hovland MusiCap and a couple Vishay
resistors(though there were later, upgraded, iterations).
If you need to replace the tweeter; search, "Dynaudio
Esotar," and include the numbers, found on yours.