RPM gauge just quit

Hi all,i have a 78 kz650,was riding yesterday everything was fine,got home,ate,went back out to ride again,and realized the rpm gauge quit working.Everything else is good.Ive checked all connections,everything seems pretty secure.Any help on this matter,before i go ripping into stuff i'm not supposed to.
Thank you

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Good Luck!

My 77 KZ650 likes to "Sleep In"when it comes to the Tach, maybe the girl thing.Thats what happens when you refer your bike as "SHE A GOOD BIKE". After it starts it takes about 4 seconds before it starts to show rpms. I would take off the cable housing at the engine and spin the inner cable with my fingers and watch the needle in the tach to see if it moves, Broken cable possible,needs lubed or inner gauge problem .