Where can i find general information about this antiquated intercom system???

I just moved my family into a big, two-story house with a NuTone Intercom system. The house is over 40 years old, and there is no telling how old this intercom system is. It doesn't work. I need to know where to find basic information about how it is hooked up, how it is powered, and how to trouble shoot this... Any help appreciated!

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