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HP 654A - 5-75. Troubleshooting Tree

HP 654A
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Section
V
Model
654A
EXAMPLE:
Suppose
that,
in
step
a
of
this
paragraph,
the
amplitude
is
found
to
be
too
high
for
one
of
the
impedances;
then
set
the
654A
AMPLITUDE
control
for
an
ac
voltmeter
indication
below
0.707V
rms,
and
vice
versa.
c.
Repeat
the
steps
of
this
paragraph
as
necessary
to
ensure
that
the
level
is
correct
for
all
impedances.
5
62.
BALANCE
ADJUSTMENTS.
5-63.
135
BAL.
a.
Perform
steps
a
and
b
of
the
Balance
Check
of
Paragraph
5-30.
b.
Set
the
654A
frequency
to
10MHz
and
adjust
A2C32 (
High
Freq.
Balance)
for
optimum
balance
(lowest
indication
on
the ac
voltmeter.)
c.
Set
the
654A
frequency
to
5MHz;
the
ac
voltmeter
indication
should
be
below
11.6mV
rms
indicating
a
balance
of
greater
than
40dB.
If
it
is
not
then
select
a
value
for
A2C21*
or
A2C36* (
but
not
both)
to
give
the
required
balance
at
5MHz.
(Typically,
balance
of
at
least
46dB,
5.8mV
rms,
can
be
achieved).
NOTE
There
is
no
way
of
predetermining
which
side
of
the
balanced
amplifier
is
unbalanced
or
what
value
of
capacitance
is
required;
A2C21*
or
A2C36*
must
be
selected
by
trial
and
error.
Select
the
lowest
value
of
capacitance
possible.
d.
Perform
steps
c
and
d
of
Paragraph
5-30 (
135
BAL
CHECK)
to
ensure
that
limits
are
met
at
all
frequencies
of
the
654A.
5-64.
150
AND
600
BAL
CHECK.
a.
Perform
the
checks
of
Paragraphs
5-31
through
5-34
to
ensure
that
balance
is
within
specifications
for
the
150
ohm
and
600
ohm
impedances.
b.
If
it is
not,
repeat
the
procedure
of
Paragraph
5-63
but
slightly
degrade
the
balance
for
the
135
ohm
impedance (
be
careful
to
remain
within
the
requirements
of
40dB
from
1MHz
to
5MHz
and
50dB
from
10Hz
to
1MHz)
then
repeat
step
a
of
this
paragraph (
5-64)
until
balance
specifications
are
met
for
all
three
impedances.
NOTE
This
situation
is
not
likely
to
arise;
however,
if
it
does,
then
it is
recommended
that
careful
notes
be
made
during
the
procedure
as
there
is
no
way,
other
than
by
trial
and
error,
of
determining
if
the
135
ohm
balance
is
being
degraded
in
a
direction
which
will
improve
the
balance
for
the
other
impedances,
or
if
it
is
being
degraded
in
a
direction
which
will
worsen
the
balance
for
the
other
impedances.
5-65.
LEVEL
FLATNESS
ADJUSTMENTS.
5-66.
75
UNBAL
FLATNESS.
a.
Perform
steps
a
through
e
of
Paragraph
5-16 (
50
UNBAL
FLATNESS
CHECK)
with
the
following
exceptions:
in
step
a.
Set
IMPEDANCE
to
75
UNBAL;
in
step
b.
Use
the
75
ohm
thermal
converter (
see
Table
5-3).
b.
Set the
654A
frequency
to
10MHz
and
adjust
A2C43 (
Frequency
Response)
for
null
indication,
+/-AE (
calculated
in
step
a
of Paragraph
5-16)
on
the
dc
null
voltmeter.
c.
Sweep
the
654A
frequency
slowly
down
to
1MHz;
the
null
voltmeter
indication
should
remain
within
+/-àE
of
null
over
the
whole
frequency
range.
NOTE
It
may
be
necessary
to
slightly
offset
the
adjustment
of
A2C43
at
10MHz
so
that
the
flatness
is
within
tolerance
across
the
X1M
range.
d.
Set
the
654A
frequency
to
10Hz;
if
the
dc
null
voltmeter
indication
is
not
within +/-
àE
of
null
change
the
value
of
A2C40*. (
Increase
the
value
of
A2C40*
if
the
654A
level
is
too
low
at
10Hz,
and
vice-versa.)
e.
Sweep
the
654A
FREQUENCY
dial
slowly
from
1
to
10
for
all
settings
of
the
FREQUENCY
RANGE
switch
to
ensure
that
the
75
ohm
output
is
flat
over
the
entire
frequency
range
of
the
instrument.
5-67.
50
UNBAL
FLATNESS.
NOTE
The
adjustments
of
Paragraph
5-66
should
be
completed
before
making
these
adjustments.
a.
Perform
steps
a
through
e
of
Paragraph
5-16.
b.
Set the
654A
frequency
to
10MHz;
the
dc
null
voltmeter
indication
should
be
within +/-
àE
of
5-18

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