CONTROL
PANEL
TROUBLESHOOTING
TACHOMETER/HOURMETER
The
tachometer!hounneter 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.
Use
the following procedures when troubleshooting a fault in
either
of
the
two
circuits
in
a tachometer/hourmeter.
Hounneter
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 the
(-)
terminal with the engine running.
1.
Voltage present - attempt adjusting the meter through the
calibration access hole.
If
no results, repair or replace the
meter.
2.
AC
voltage not present - check for proper alternator
DC
output voltage.
3.
Check for
AC
voltage at the tach terminal on the alterna-
tor to ground.
4.
Check the electrical connections from the tachometer
input terminal to the alternator connection.
Tachometer
Sticking
1. Check for proper
AC
voltage between the tachometer
input terminal and the
(-)
terminal.
2.
Check
f~r
a good ground connection between the meter
(--)
terminal and the alternator.
3.
Check that the alternator is well grounded to the engine
block at the alternator pivot bolt.
Tachometer
Inaccurate
1. With a hand-held tach
on
the front
of
the crankshaft pul-
ley retaining nut
or
with a strobe-type tach, read the front
crankshaft pulley rpm.
Set the engine with a hand
or
strobe tach at
1500-1800
rpm.
2. Adjust the
tachometer- with a small Phillips
type
screw-
driver through the calibration acess 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
2500-3000
rpm). (Adjust the tach
as
needed.)
COARSE
ADJUSTMENT
CURRENT
TACHOMETER
EARLY
MODEL
TACHOMETER
EARLY
MODEL
TACHOMETER
(-)
GROUND
(-)
GROUND
TERMINAL
TACHOMETER
INPUT
(AC
VOLTAGE)
Engines & Generators
51
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