TACHOMETER
TROUBLESHOOTING
TACHOMETER/HOURMETER
The tachometerlhounneter used
in
propulsion engine
instru~
ment panels contains two separate electrical circuits with a
common ground.
One
circuit operates the hounneter and the
other the tachometer.
The
hounneter 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
Yolts,
fed
from one
of
the diodes
in
the alternator and supplied to the
"tach iop." terminal while the engine
is
running, and the
alternator producing battery charging voltage
13.0 - 14.8
volt, DC.
The following are procedures
to
follow when troubleshooting
a fault
in
either
of
the two circuits
in
a tachometerlhounneter.
Hourmeter
Inoperative
Check for the proper
DC
voltage between (+) and (-) termi-
nals.
a.
Voltage present - meter
is
defective - repair or replace.
b.
Voltage not present - trace (+) and (-) electrical connec-
tions for fault. (Jump
12
volts DC to meter (+) terminal to
verify the operation.)
Tachometer
Inoperative
a.
Voltage present - attempt adjusting meter through cali-
bration access hole. No results, repair or replace meter.
h.
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 "tach inp." terminal to
alternator connection.
Tachometer
Sticking
a.
Check for proper AC voltage between "tach inp." tenninal
and (-) terminal.
h.
Check for good ground connection between meter (-) ter-
minal and alternator.
C.
Check
that alternator
is
well grounded to engine block at
alternator pivot bolt.
Calibration
a.
With a hand-held tach
on
the front
of
the crankshaft pul-
ley retaining nut
or
using a
strohe
type lach, read the front
crankshaft pulley rpm.
b.
Adjust the
tachometer
with a sma\! Phillips type screw-
driver through the calibration
access
hole
in
the rear
of
the
tachometer.
Zero
the tach
and
bring
it
to
rpm scI by
using
a strobe
or
hand tach (verify rpm at idle and at high
speed
1500 - 2500 -
3000
rpm). Adjust the tach as needed.
NOTE:
Current modellachometers use a coarse adjustment
dial to set the tachometer
[0
the crankshaft pulley
rpms_
The
calibrating screw is
[hen
used for fine luning.
LIGHT
TACH
INP
CALIBRATE
EARLY
MODEL
TACHOMETERS
(-)
TERMINAL
1-)
TERMINAL
~~
COARSE
AOJIJST"ENT--f:jj~
1-)
TERMINAL
CURRENT
TACHOMETER
~"ZlIt----I+)
TERMINAL
FINE
CAI.lBR'ATING.-~~~:"~
INP
29
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