Heathkit IM-16 - Troubleshooting; General Troubleshooting Information

rotation, first
turn the lmob
all
the
way
in
one
direction
(until
the
three
balls in
the
rear
of
the
control
stop
turning). Then
attach
a
small
piece
of
tape to the
knob and turn the
knob five
revolutions in the
opposite
directionandremove
the tape.
(
)
Check the
position
of
the meterpointer,If
it
does
not rest directly
over
the
"0"
marks at
the
left end
of
the
scales,
turn the
meter
zeto
screw with a
small screwdriver. The
meter
zero
screw should
only
be adjusted
during
the
calibration of
the instrument.
(
)
Plug
the
probe
phone
plug
into the
input
jack,
and turn the
probe
switch
to DC.
Clip
the
common test
lead
to the
probe
tip.
(
)
Connect
the
line
cord
plug
to an
AC
outlet.
(120
volt if
you
wired
the Voltmeter
for
120
volt
operation,
or
240
volt if wired
f.cjr 240
volt
operation.)
(
)
Turn
the POWER
switchtoLINE.Themeter
pointer
should deflect
off-scale
to
the
left.
(
)
Very
slowly turn the BIAS
adjustment
until
the
meter indicates
"0".
(
)
Turn
the
ZERO
ADJUST
controlfullyclock-
wise.
The
meter should
indicate
approxi-
mately
15
on the
black
50 scale.
(
)
Turn
the ZERO
ADJUST
control
counter-
clockwise
until the
meter indicates
zero.
Then
change
the FUNCTION
switch
to
DC-,
and
continue
to
turn the ZEP'O
ADJUST
control
until fully
counterclockwise.
The
meter
should
again indicate
approximately
15 on
the
black 50 scale.
(
)
Return
the ZERO ADJUST
control to the
center
of
its
rotation where
the meter
indicates
zero. Set this
control
carefully
so
the
meter
remains atzerowhilechanging
the FUNCTION
switch back and
forth
be-
tween
DC-
and DC+.
DC CALIBRATION
The DC
calibration
of
theVoltmetercanbemade
with
a fresh
(unused)
C-cell
battery.
However,
if a highly
accurate voltmeter or
a dependable
.5
volt
referencevoltage is available, calibration
accuracy may
be
improved.
A
fresh C-cell
battery
should measure
1.55 volts.
The
red
dot
at the
right-hand
endofthe
15
scale
indicates this
1.55 volts when
the VOLTS
range
switch
is
in the
1.5
position.
Perform
the
following
steps to
calibrate the DC
scale with
a fresh C-cell
battery. You may
use the
ohms
battery for these
steps.
(
)
Turn
the VOLTS
range switchto
1.5, andthe
FUNCTION
switch
to DC+.
Zero
the
meter
with the
ZEPIO
ADJUST
control.
(
)
Touch
the
common test
lead to the negative
end, and the
probe
tip to the
positive
end
of
the C-cell
battery.
(
)
Carefully
adjust the DC Calcontroluntilthe
meter
pointer
rests
over
the
red
dot
at the
right
of
the 15
scale.
_
DC
calibration
is now
complete.
If
you
have an-
other
accurate
voltmeter
or
reference
voltage,
you
may wish to
check
the DC
calibration by
comparison.
AC
CALIBRATION
An
AC
voltage
source
and another
AC
voltmeter
are
required for accurate
AC
calibration. How-
ever, the
AC
line voltage may
be used for nom-
inal accuracy,
as described
in
the
following
steps.
(
)
Turn the FUNCTION
switch to
AC,
and the
test
probe
switch
to the
AC
position.
(
)
Set the VOLTS
range
switch
to
150
if
your
Voltmeter
was wired
for 120 volt operation
(500
if
wired
for
240 volt
operation).
CAUTION: Use
extreme
care
when
measuring
line voltages.
Personal
shock
or
instrument
damage
could result from
carelessness,
NOTE: The
common
test
lead will connect
one
side of
the
power
source directly
to the
sub-
panel
in the
Voltmeter. Be
sure
to
connect
the
eommon
test
lead
to the
ground
side
of
the
volt-
age source. Use a screwdriver withaninsulated
handle
to
make
AC Cal
adjustments
on
the sub-
panel.