MCI Sony JH-110 (JH-24) Optical Tach Replacement

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mediatechnology
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Re: MCI Sony JH-110 (JH-24) Optical Tach Replacement

Post by mediatechnology » Mon May 15, 2017 7:56 pm

Guy -

Working backwards from the LM2907 schematic it looks like the tach motor was 5V @ 1000 RPM.
I seem to recall about 7V in full wind?

Servotek Type-A DC Tachometers https://www.marshbellofram.com/servo-te ... enerators/

The formula for the LM2907 is Vout = 12V * 1000pF * fin * R.
The LM2907 output is multiplied by two.

A 360 cpr codewheel (6 kHz at 1000 RPM) using 1000 pF (5%) and 39K works out to be about 5.6V at the final output.
A 500 cpr codewheel (8.33 kHz at 1000 RPM) using 1000 pF and 24.9K 1% provides almost exactly 5V.
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