Automobiles are NOT the cleanest environment in town. Is it possible
that dirt has entered the movement? Is it a highly sealed movement? I
sort of doubt that being an in expensive auto product. Does it have a
removable lamp on the meter where dirt could get in? Ira.
On 8/16/2021 3:53 PM,
Thanks guys, that pretty much lines up, with what I was thinking...Sadly,
since it seems to be frequency based, I don't see a failure mode that
would duplicate the problem I'm having other than the meter itself.
It's odd as the problem first showed up when the sense wire, connected to
the
I think bunge.pip described it pretty accurately. (Charge pump / voltage
doubler - tomato / tomahto) In this case the doubler actually generates a
voltage that's negative with respect to ground, which is why the meter
polarity is "backwards". All the circuitry to the left of the module is
It's a charge pump. VR1 fixes the pulse amplitude so the tach is not
sensitive to battery voltage. C2 determines the charge per pulse and the
meter averages the current because it cannot follow the pulses fast enough.
R6 calibrates it.
I suggest putting a 'scope on it and follow the pulses from
I hope I can be forgiven for this.. ;) I had a TIA in February and my head
still isn't working quite right..
Going to have to work on my OLD (1962) GM tachometer. It will only go up to
3,000rrpms, then stop. It really doesn't 'look' like the meter movement
sticks at that point, though I guess
