Hey Thomo!
Those are very nice!
Before you remove the tweeters, try spinning the the tweeter level pot adjustments back and forth a lot to see if you can get a signal to the tweeters. You may find a sweet spot where it comes to life. A corroded pot is most likely the cause of your silent tweeters.
Remove the woofers and fiberglass to gain access to the pots. Pop the wire retainers, lift the tops off and inspect the pot wipers and contact disks. There’s a good chance you’ll see lots of green corrosion. If so, you’ll need to remove them for cleaning and inspection. I soak mine in a clear distilled vinegar and salt solution for an hour or so, then wash and rinse with soap and water. Inspect the disk surface condition for deep pitting and or actual material missing, very common. If there’s only minor pitting, sand smooth with a flexible sanding disk and a Dremel. Next is the pot wiper’s condition. Some are fine, others may have worn through with a small hole, others have the tip completely corroded away.
Let us know what you discover.
Glenn