Ed Lijewski wrote:Why would you infer that I wouldn't note first and return the potentiometer to its original setting? Doing that procedure has returned normal function to lazy/non operating tachs.
The reality is that neither you nor I know the scaling value of that potentiometer. If the scaling value is large then a tiny bit of variation from the pre-adjustment to post-adjusment position will make a big difference. You can mark it but you'll never get it back to exactly where it started from. Without having something to compare it to before and after you moved the potentiometer you really are guessing when you say it's operating correctly after moving the potentiometer around.
We're moving quickly into the arena of "how accurate is the stock tach, really" and "does the accuracy of the stock tach really matter?" If we're not worried about getting it back in exactly the place it started from (this is what is going to happen if you move it without anything to compare it to before and after you move it) and we don't know the scaling function of that potentiometer, then does it really matter if the tach is lazy or not? It's going to be wrong when it's lazy and it's going to be wrong after the potentiometer gets moved. You're breaking/denying the 0th Law of Thermodynamics if you say otherwise.
I think the bottom line is that if you have resoldered the board and the tach is still lazy, then try the potentiometer movement. Your tach sucked before you moved the potentiometer so if, after you moved it and then returned it to its original setting, it "looks right" but you don't know that it is right, then I guess you can feel better about the tach function. And that's the key here,
I think.
I know I like my car a little bit more with my functioning tach. The tach may still be lazy (for example, the tach might read 4500 rpm when the engine is turning 5000 rpm) but it really doesn't matter. If it mattered, I would remove that tach and put a real one in there.
