1970 Camaro SS Tach

Have a tach in a 1970 camaro SS that isn't working.
We found the tach wire, and hooked it up, and it's hooked up correctly at the cluster harness, but the tach doesn't work.

We took the tach out of the cluter, and it has two wires (white and black) coming out of it, which goes to a small little circuit board type thing

is there any way to test this tach? do they usually go bad?

the engine is a 396 and it has HEI, I believe.

any help is appreciated.

THE tachs in the early cars are kinda known for their failure but you can use one out of a later model car which would probably work better with HEI (the 70 would have had a coil and points ) and if you are carefull you can switch the gage faces on 75-77 with the 70 the sweep is the same(I think ) someone correct me if im mistaken.. and the gage is set up for HEI after 75 ,otherwise why not get an aftermarket one they offer more features and are reliable .. unless you are restoring then I dont think its cost effective to repair it ..