HP 339A - Page 25

Model
339A
Section III
should
indicate
-3dBV±2dB.
Return
the
filter switch to
off
(out).
h.
Set
the
FREQUENCY
controls
for
a
frequency
of
80
kHz.
Readjust
the
level vernier
for a
meter
indication
of 0
dB
V
if
necessary.
i.
Set
the 80 kHz
filter
switch
on
(in).
The
meter
should
indicate
-3
dB
V
±
2 dB.
Return
the
filter
switch to off
(out).
3-56.
OPERATOR’S
MAINTENANCE.
3-57. Fuse
Replacement.
3-58.
The
ac line
fuse is
located on
the
rear pane! of the
instrument.
Before
checking or
replacing
the
fuse,
disconnect
the ac
line cord
from
the
instrument.
The fuse
used
in
the
Model 339A
is a
250 mA,
normal-blow fuse.
WARNING
|
'
For
continued
protection
against
fire
hazard,
replace only
with
the
same type and
rating
of
fuse
as specified
for
the
line
voltage being
used.
3-59.
Adjustment of
Meter Mechanical
Zero.
3-60.
The
meter
is
properly
zero-set
when the pointer
rests
over the
zero
calibration mark
with the
instrument
in its
normal
operating
environment and
turned off.
Zero-set the
meter as
follows to
obtain
maximum
accuracy
and
mechanical
stability:
a.
Turn
instrument
on
and
alow it to
operate
for
at
least
20
minutes to
let meter
movement reach
normal
operating
temperature.
b.
Turn
instrument off and
allow
30
seconds
for all
capacitors
to discharge.
c.
Rotate zero
adjustment
screw
clockwise
until
pointer is
left of zero and
moving
upscale.
d.
Continue
rotating screw
clockwise; stop
when
pointer is
exactly
at zero.
e.
When pointer
is exactly
over zero,
rotate
adjustment
screw
slightly
counterclockwise
to
relieve
tension on
pointer
suspension. If
pointer
moves off zero,
repeat Steps
c through e.
but make
counterclockwise
rotation less.
3-7
3-8