HP 6296A - Page 38

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5-27
TROUBLE
ANALYSIS
5-28
General.
Before
attempting
to
trouble
shoot
this
instrument,
ensure
that
the
fault
is
with
the
instrument
and
not
with
an
associated
circuit.
The performance
test
(Paragraph 5-10)
enables
this
to
be
determined
without
having
to
remove the
in-
strument
from
the
cabinet.
5-29
Once
it
is
determined
that
the
power
supply
is
at
fault,
check
for
obvious
troubles
such
as
open
fuse,
a
defective
power
cable,
or
an
input
power
failure.
Next,
remove
the
top
and bottom
covers
(each
held
by
four
retaining
screws)
and
inspect
for
open
connections,
charred
components,
etc.
If
the
trouble
source
cannot
be
detected
by
visual
inspection,
follow
the
detailed
procedure
outlined
in
succeeding
paragraphs.
Once
the
de-
fective
component
has
been
located
(by
means
of
visual
inspection
or
trouble
analysis)
correct
it
and
re-conduct
the
performance
test.
If
a
compo-
nent
is
replaced,
refer
to
the
repair
and
replace-
ment
arxi
adjustment
and
calibration
paragraphs
in
this
section.
S-30
A good
understanding
of
the
principles
of
operation
is
a
helpful
aid
in
troubleshooting,
and
it
is
recommended
that
the
reader
review
Section
IV
of
the
manual
before
attempting
to
troubleshoot
the
unit
in
detail.
Once
the
principles
of
operation
are
understood,
logical
application
of
this
knowledge
used
in
conjunction
with
the
normal
voltage
readings
and
wavefcrms
shown
on
the
schematic
and
the
ad-
ditional
procedures
given
in
the
following
para-
graphs
should
suffice
to
isolate
a
fault
to a compo-
.-ient
or
small
group
of
components.
The component
location
diagram
at
the
rear
of
the
manual
can
be
consulted
to
determine
the
location
of
components
and
test
points.
The normal
voltages
shown
on
the
schematic
are
positioned
adjacent
to
the
applicable
test
points
(identified
by
encircled
numbers
on
the
schematic
and
component
location
diagram). Addi-
tional
test
procedures
that
will
aid
in
isolating
troubles
are
as
follows:
·a.
Reference
circuit
check
(Paragraph
5-31).
This
circuit
provides
critical
operating
voltages
fa
the
supply
and
faults
in
the
circuit
could
affect
the
overall
operation
in
many
ways.
This
circuit
should
be
checked
first,
before
proceeding
to
other
areas
of
the
unit.
b.
Series
regulator
and
preregulator
feedback
loop
checks
(Paragraph
5-32).
c.
Procedures
for
dealing
with
common
troubles
(Paragraph
S-33}.
5-31
Reference
Circuit.
a.
Make
an
ohmmeter
check
to
be
certain
that
neither
the
positive
nor
negative
output
termi-
nal
is
grounded.
b. Turn
front-panel
VOLTAGE
and
CURRENT
controls
fully
clockwise
(maximum).
c.
Turn
on
power
supply
(no
load
connected).
d.
Proceed
as
instructed
in
Table
5-2.
5-32
Series
Regulator
and
Prerequlator
Feedback
Circuits.
GenerallY>
malfunction
of
these
two
feed-
back
circuits
is
indicated
by high
or
lQw
(or
no)
output
voltage.
If
one
of
these
situations
occur,
disconnect
the
load
and
proceed
as
instructed
in
Table
5-3
or
5-4.
Preregulator
waveforms
are
in-
cluded
on
the
schematic
at
the
rear
of
the
manual.
5-33
Common
Troubles.
Table
5-6
lists
the
symptoms,
checks,
and
probable
causes
for
com-
mon
troubles.
S-34
REPAIR
AND
REPLACEMENT
5-35
Before
servicing
a
printed
wiring
board,
refer
to
Figure
5-10.
Section
VI
of
this
manual
contains
a
list
of
replaceable
parts.
Before
replacing
a
semiconductor
device,
refer
to
Table
5-7 which
lists
the
special
characteristics
of
selected
semi-
conductors.
If
the
device
to
be
replaced
is
not
listed
in
Table
5-7,
the
standard
manufacturers
part
number
listed
in
Section
VI
is
applicable.
After
replacing
a
semiconductor
device,
refer
to
Table
5-8
for
checks
and
adjustments
that
may be
necessary.
Table
5-2.
Reference
Circuit
Troubleshooting
Step
Meter
Meter
Normal
Common
Positive
Indication
If
Indication
Abnormal. Take
This
Action
1
+S
29
9.
4
%0.
4Vdc
Check
15. 4
volt
bias
or
VR600
2
28
+S
6. 2
+O.
3Vdc
Check
diode
VR601
3
+s
30
15. 4 +o.
5Vdc
Check
R605,
Q600
through
Q603, C600,
CR600
and
CR601 •
S-7