T5 Tachometer

Can someone explain the inner workings of the Digital tach on these things?

And when they fail but yet everything else is working is the root of this evil within the Curcuit board itself?

And is there a source of these boards if one was to need one? In the USA preferably but not picky…

And anyone got a scouce of these Nakasil coated barrels yet? I saw one earlier post looking around for one. I think I know where pistons are but would love to lay a barrel into stock due to the rareness of them and my dam typical luck!