Quote:
Originally Posted by ghlkal
My tach is also way off (maybe not 2K at idle, but not close to being accurate)
I had read that ~300K ohms was needed. Paul's suggestion of a pot is a good one. Thanks for the procedure too, Paul
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Yes, I studied that too, and determined the deteriorating resistor in the pack was not removed, thus left to continue to affect the calibration again as it continues to change;
sorta like painting over rust!
Clipping the leads on the offending resistor pack removes at least that resistor from ever affecting the calibration again. As for the discrepancy between the 300k reference and the 140-220k (this procedure) is because resistors
in parallel result in less resistance across them than the lowest value. The combination of the failing resistor and an arbitrary value like 300k Ω could result in exactly the value needed...or miss, depending on what the true value should be.
Rt = 1/((1/r1)+(1/r2)...) where (parallel) Resistance total can be determined for different variables of two or many parallel resistor values.
Example: a 300k in parallel with another 300k would result = 1/((1/300)+(1/300)) = 150k R(total)
This little formula and possibly adding resistors in series can be used to hone in on the exact value needed.
P.