Service manual

TACHOMETER
TACHOMETER/HOURMETER
The tachometerlhourmeter used in propulsion engine instru-
ment panels contains two separate electrical circuits with a
common ground.
One circuit operates the hourmeter and the
other the tachometer. The hourmeter 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 tachometerlhourmeter.
Hourmeter Inoperative
Check for the proper DC voltage between (+) and (-)
terminals.
a. Voltage present - meter is defective - repair or replace.
b. 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.
a. Voltage present - attempt adjusting meter through cali-
bration access hole. No results, repair or replace meter.
b. AC voltage not present - check for proper alternator
DC output voltage.
c. Check for AC voltage at tach terminal on alternator to
ground.
d. Check electrical connections from tachometer input
terminal to alternator connection.
Tachometer Sticking
a. Check for properAC voltage between "tach inp." ter-
minal and (-) terminal.
b. Check for good ground connection between meter (-)
terminal and alternator.
c. 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. Set the engine with a hand
or strobe tach
at 1S00-1800 rpm.
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 set
by the strobe
or hand tach. (Verify the rpm at idle and
at high speed
2S00-3000 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
~0IZ'l..,--(+) TERMINAL
EARLY MODEL TACHOMETER
TACHOMETER INPUT
(AC VOLTAGE)
. CALIBRATION
(-) GROUND
,TERMINAL
TACHOMETER INPUT
(AC VOLTAGE)
EARLY MODEL TACHOMETER
Engines & Generators
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