Case backhoe: tach works, hr mtr doesn't

What is strange is that the hour meter is built in to the tach. I figured that if the tach is responding, it should be driving the hour meter as well. At least, that is how it works on my Ford 650 tach.

I have not yet looked to see if there is a separate connection for the hour meter- if so, that would steer me to an external source of the problem. If indeed the hours should be counting as the tach revs, then it must be a problem internal to the meter.

Any ideas here?
Thanks.

I am not famaliar with the 580 but Case 530 and lower nr series tractors are drag cup. The tach cable spins a permanent magnetic inside a cup that has a spindle attached with the pointer on the end. The cup deflects relative to the magnetic force generated by the speed of the tach cable and thus the sweep of the pointer across the gauge face. The hour counter is driven mechanically by the tach cable via a worm gear, an immediate spur gear and a small spur gear on the counter drum. If any of the 3 gears strip or not in driving contact, the tach will continue to display and but the counter will not change.

Joe