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6.1
INTRODUCTION
This section
is
organized
as
follows:
Circuit
Board
Access
Basic Techniques
Troubleshooting
I
ndividual
Components
Troubleshooting
Guide
(Refer
to
paragraph
5.2
for
required
test
equipment.)
NOTE
Wavetek
maintains
a factory
repair department
for
those customers
not
possessing
the
necessarY
personnel
or
test equipment
to
maintain
the
instrument.
lf
an instrument
is
returned
to
the
factory
for
calibration
or
repair,
a
detailed
description
of
the
specific
problem should
be
attached
to minimize
turnaround
time.
6.2
CIRCUIT
BOARD
ACCESS
Turn the
instrument over,
remove
the
four
screws
in
the
bottom
cover
and
remove
the
bottom
cover.
For
sweep
board and XCG board
access,
remove
the
four
screws hold
ing
the
main
board
to
its
long standoffs, place
the
instrument
right
side
up and carefully
remove
the
top
cover.
6.3
BASIC TECHNIOUES
Troubleshooting requires no
special
technique. Listed
below
are
a few
reminders
of
basic electronic
fault
isolation.
1.
Check
control
settings
carefully.
Many times
a
seem-
ingly malfunction
is
an
incorrect
control
setting, or
a
knob that
has loosened
on
its
shaft.
2.
Check associated
equipment
connections. Make
sure
that
all
connections
are
securely
connected
to
the
correct connector.
Perform the
calibration
procedure. Many out-of-speci-
fication
indications
can
be corrected
by
performing
specific
cal
ibration
procedu
res.
SECTION
TROUBLESHOOTING
Visually
check
the interior
of
the
instrument.
Look
for
such indications
as
broken wires, charred compo'
nents,
and
loose
leads.
6.4
TROUBLESHOOTING
INDIVIDUAL
COMPONENTS
6.4.1
Transistor
A
transistor
is
defective
if
more
than
one
volt
is
measured
across
its
base
emitter
junction
in
the
forward
direction.
A
transistor when
used as
a
switch may
have a
few
volts
reverse bias voltage.
lf
the
collector
and
emitter
voltages
are
the
same,
but
the
base
emitter voltage
is
less
than
500 mV
forward
voltage
(or
reversed bias),
the transistor
is
defective.
A
transistor
is
defective
if
its
base
current
is larger
than
10%
of
its emitter
current
(calculate currents
f
rom voltage
across
the
base
and
emitter
series resistors).
6.4.2
Diode
A
diode
is
defective
if
there
is
greater
than
1
volt
(typically
0.7
volt)
forward
voltage across
it
(except
Zener
and LED).
6.4.3
Operational
Amplifier
The
"+"
and
tt-"
inputs
of
an operational amplifier will
have
less
than
15 mV
voltage
difference when
operating
under normal conditions.
lf
the output
voltage stays
at
maximum positive,
its
"+"
input
voltage
should be more positive
than
its
"-"
input
voltage,
or
vice
versa; otherwise,
the
operational amplifier
is
defective.
6.4.4
FET Transistor
No
gate
current should be drawn
by the
gate
of
an
FET
transistor.
lf
so,
the transistor
is
defective.
The
gate-to-source
voltage is always
reverse biased
under
a
normal operating
condition;
e.g.,
the
source
voltage
is more
positive than
the
gate
voltage
tor
2N5485, and
the
source
6-1
4.
3.
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