Service manual

TACHOMETER
TACHOMETER/HOUR METER
The tachometerlhour meter used in propulsion engine instru-
ment panels contains two separate electrical circuits with a
common ground.
One circuit operates the hour meter and the
other the tachometer. The hour meter circuit operates on 12
volts alternator charging voltage supplied to the
(+) terminal
on the back
of the instrument.
The tachometer circuit operates on AC voltage 6-8 volts, fed
from one
of the diodes in the alternator and supplied to the
tachometer input terminal while the engine is running, and
the alternator producing battery charging voltage 13.0-14.8
volts
DC.
The following are procedures to follow when troubleshooting
a fault in either
of the two circuits in a tachometerlhour
meter.
Hour meter Inoperative
. Check for the proper DC voltage between (+) and (-)
terminals.
1. Voltage present - meter is defective - repair or replace.
2. Voltage not present - trace
(+) and (-) electrical con-
nections for fault. (Jump 12 volts DC to meter (+)
terminal to verify the operation.)
Tachometer Inoperative
Check for the proper AC voltage between tachometer input
terminal and (-) terminal with the engine running.
1. Voltage present - attempt adjusting meter through calibra-
tion access hole. No results, repair or replace meter.
2. AC voltage not present - check for proper alternator
DC
output voltage.
3. Check for AC voltage at tach terminal on alternator to
ground.
4. Check electrical connections from tachometer input
ter-
minal to alternator connection.
Tachometer Sticking
1. Check for proper AC voltage between "tach inp." terminal
and (-) terminal.
2. Check for good ground connection between meter (-)
ter-
minal and alternator.
3. Check that alternator is well grounded to engine block
at
alternator pivot bolt.
Tachometer Inaccurate
a. With a hand-held tach on the front of the crankshaft
pulley retaining nut or with a strobe-type tach, read the
front crankshaft pulley rpm at idle.
b. Adjust the tachometer with a small Phillips type
screw-
driver through the calibration access hole in the rear of
the tachometer. Zero the tach and bring it to the rpm
indicated by the strobe
or hand tach. (Verify the rpm at
idle and at high speed
3000-3600 rpm). (Adjust the tach
as needed.)
NOTE: Current model tachometers use a coarse adjustment
dial
to set the tachometer to the crankshaft pulley rpms. The
calibrating screw is then used for fine tuning.
COARSE
ADJUSTMENT
~~-II+1 TERMINAL
TACHOMETER INPUT
ClJRRENT TACHOMETER (AC VOLTAGE)
(-) GROUND 71
,TERMINAL,. LIGHT ~!
(+) TERMINAL
(-) GROUND
TERMINAL
TACHOMETER INPUT
(AC VOLTAGE)
EARLY MODEL TACHOMETER
Engines & Generators
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