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10del654A
e;
is
Ie
y,
)f
is
ill
er
a
:e
ph 5-16(50
.
1 e following
lAL
;
Invert
er
(see
and
adjust
I
indication,
ph
5-16) on
vn
to
I
MHz;
main
within
I
range
.
the
hat
the
the dc null
-t1E
of null
the value of
It
10Hz,
and
owly from 1
CY
RANGE
utput is flat
instrument.
-66
ese
5-16.
the
dc null
1
+/-t1E of
Model
654A
null. If it
is
not change
the value
of A4Cl
*
to
bring
the
654A
level
within
tolerance
(decrease
A4C
I
*
to
increase
the
output
level and
vice-versa).
c. Sweep the
654A
frequency
slowly
down to I
MHz
and observe
the dc
null
voltmeter indication which
should
remain
within
+/-t1E
of null.
If it does
not
repeat step b
of
this
paragraph but
select a value
for
A4C I
*
which allows the
flatness to
be met
across
the IMHz to 10MHz
frequency range.
d.
Check
the
654A
flatness
over
the 10Hz to
I
MH
z
ranges
as
before.
5-68. 135, 150 and 600 BAL
FLATNESS.
5-69.
Check the
flatness
for the balanced impedances by
performing
Paragraphs
5-IS, 5-19 and 5-20. There are
no
adjustments
to be made
for
these ranges
.
5-70. TROUBLESHOOTING THE 654A.
5-71.
This section contains information
and
procedures
designed to aid in
the process of isolating
malfunctions.
Troubleshooting
should
be undertaken
only after
it has
been determined
that
the malfun ction cannot be
corrected
by performing
the
adjustment
and
calibration procedures.
5·72. When
a malfunction
occurs first
ensure
that the
trouble
is not
caused
by
conditions
external
to the
umen!; th en
make
the front
panel checks
described in
Paragraph
5-74
be fore proceeding to the Troubleshooting
Tree.
5-73. The
Troubleshooting
Tree (Figure
5-IS)
illustrates
a
systematic
method
of loca
ting a faulty
circllit.
Additional
checks (including
Visual)
and
measuremen
ts will
be required
to isolate
the faulty
component.
5-74.
FRONT PANEL CHECKS.
a.
Check
that the LINE ON lamp is lit; if it
is
not
,
ch
eck
the
setting of the
I 15/230V
slide switch,
check the
fuse (FI) and
if
necessary
check
the
primary circuit
of
the power transformer (T
J
on
schematic
No.4
,
Figure
7-5)
.
b. In
this
procedure
the
654A will
be swept
across its
frequency range while the
following
points
are
monitored
:
A.
the COUNTER OUTPUT
B.
the 654A
meter indication
C.
the front panel
output
connectors.
By applying
the
observation made
to Table
5-5 it
should be possible
to
localize
any problems to
a
particular
area in the
instrument
(refer also
to
the
Block
Diagram,
Figure
7-1).
Section
V
I) Set the
654A controls as follows:
AMPLITUDE
........
....
fully clockwise
OUTPUT LEVEL
dBm . .
. . .
. .. .
....
+
10,0
IMPEDANCE
.............
.
. .
50UNBAL
2) Connect an oscilloscope or ac
voltmeter
,
through
a 50 ohm
feedthrough termination
,
to
the
654A
rear panel
COUNTER
OUTPUT.
3) Connect
an
oscilloscope
or
ac
voltmeter
,
through
a
50
ohm
feedthrough termination, to
the
front
panel
UNBAL out put connection.
4) Sweep
the
654A
FREQUENCY
dial
slowly
from
1 to
10
(for all
positions
of
the
FREQUENCY RANGE
switch)
while
observing
the three monitoring points
A,
Band
C.
5) Select
from
the
left hand
column of
Table
5-5
the
ABC
combination
which
corresponds
with
the
observations
made in
step 4).
The
center
col
umn
of
Table
5-5 gives
the most likely
trouble
area
for each
combination
and the right
hand
column indicates
the
next step to make
in
trou bleshooting.
5-75. TROUBLESHOOTING TREE.
5-76.
To use
the
tree
start
at
CD, read
stepCDof
Paragraph
5-77 and
make the required
check:
the next
step
then
depends upon whether the
first
check
was
a
PASS
or
FAIL.
Several
o
f the
FAIL
branches
split
into
sub-branches,
take
the sub-branch
which
best
fits
the
observations
made.
At
each
step of
the tree it is
important
to
read
the appropriate
step
o
f Paragraph
5-77 as
the
tree
itself
does not
give
sufficiently
detailed
information,
in
most cases, for
the
check
to be made. Refer
also
to the Block Diagram and
Schematics
of Section
VlI
when
using the troubleshooting
tree. If
yo
u
complete
the
tree
and
still
have failed
to
localize
the
problem area then refer to Paragraph
5-7S
for
additional information_
5·77.
This paragraph provides information for each
step of
the
tro
ubleshooting tree
.
- - - - - N O T E - - - - - -
Make the Front panel checks,
described
in
Paragraph
5-74,
if
you
have
not already
done so.
CD
Check
with
an oscilloscope
at
A2
Pin
4:
there
should be a
sine wave of
between
5.5V and
7V
POp.
Sweep
the
FREQUENCY
dial
from
I to 10
for all
positions
of
the range
switch.
If
the
signal
appears
,
even momentarily,
then the problem
is
probably
frequency
calibration.
5-19
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