95-23 Engine (N
2
) and Rotor Dual Tachometer
A. Description
CAUTION
Installation of electrical devices can affect accuracy and
reliability of electronic tachometers.
An electronic engine (N2) and rotor dual tachometer is standard. Engine tachometer
signal is provided by a transducer on the engine gearbox. Rotor tachometer signal is
provided by magnets on the main gearbox tail rotor driveline yoke. Each tachometer
is on a separate circuit with its own circuit breaker.
The tachometer bus receives power from the avionics bus or through the battery
relay bypass circuit as long as the main rotor gearbox has oil pressure. Therefore, the
tachometers will receive power through the bypass circuit whenever the rotors are
turning even if the avionics bus is not powered. The bypass circuit is disconnected
from the tachometer bus when the annunciator test button is depressed. Pressing
the test button while the helicopter is running will confirm that the tachometers are
receiving power from the avionics bus.
NOTE
Do not use magnetized tools.
CAUTION
Protect instrumentation using foam padding or equivalent.
Handle instruments like eggs.
B. Removal
1. Turn battery switch off and pull out TACHS N
2
(2 amp) and R (2 amp) circuit
breakers on circuit breaker panel.
2. Remove perimeter screws securing instrument face to console and pull face aft.
3. Remove screws securing console harness connector to F792-1 dual tachometer
and unplug connector.
4. Supporting instrument, remove screws securing tachometer to face, and remove
tachometer.
Page 95.8
Chapter 95 Instrument System APR 2019
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