Tach on KZ550A

Im almost done getting my KZ in great running shape. But I can't seem to get the tach working. I ordered a new cable thinking it was that. The tach goes up to only about 2-3k. It's like the square drive is slipping on either end of the cable. Or the tach insides are shot. Is there a quick way to narrow it down? Are the tachs rebuild-able if it is in fact the mechanics in the gauge.

Thanks!!

Contact www.z1enterprises.com They have a speedometer and Tach service they send instruments to for repair. The company does only certain years of tach/speedometers.