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It is very possible that Lurch is correct and the spine is broken. The shutoff works on an overload principle. When the antenna bottoms up e breaker or down, the extra resistence trips the breaker and shuts it off. If the mast spind is broken, it never sees that rsistence.
It is possible to have some drive mechanism broken also but you should be able to remove the mast by removing the collar on top and pulling it out. If it pulls out, it's broken.