Dead Marantz Vintage speaker

Pull the cross over and check for buldging or leaking or popped capacitors. Also check for burnt resistors (although if it's reading correctly at the connectors I doubt that is your problem). Check the soldered areas where the components connect to the board as well, you may find something came loose. Also check where the speaker connections connect to the crossover board.

Other than that, I recommend popping over to Audiokarma.org and asking there because all the old pros live there and one of them can probably tell you what is wrong and how to fix it.

2nd that... pull that Xover and replace bad caps, had to do the same on 3 sets of vintage KLH. Partsexpress.com dayton caps work just fine for the money.