Troubleshooting; Factory Repair; Troubleshooting Tables; Troubleshooting Individual Components - Wavetek 188 Instruction Manual

SECTION
U
TROUBLESHOOTING
6.1
FACTORY
REPAIR
Waveiek
maintains a
factory reoair
department
for
those
customers
not
possessing the necessary
per-
sonnel
or
test
equipment
to maintain the instrument.
If
an
instrument
is
returned
to
the
factory
for
alignment
or
repair,
a
detailed description
of the
specific prob-
lem
should be
attached
to
minimize turnaround time
6.2
TROUBLESHOOTING TABLES
Table
6-1
gives an
index
of the
troubleshooting
tables
by
indications of
common
problems The
tables
do not
cover every
possible
trouble, but.
when
used
in
con-
junction
with
circuit descriptions
and
schematics,
will
be an
aid
in
systematically
isolating faulty
components
6.3
TROUBLESHOOTING
INDIVIDUAL
COMPONENTS
6.3.1 Transistor
1
A
transistor is defective
if
more
than one
volt
is
measured
across
its
base-emitter junction
In
the
forward
direction.
2.
A
transistor
when
used as a switch may
have
a
few
volts
reverse bias voltage across base-
emitter junction
3.
if
the collector and
emitter voltages are the
same,
but the base
emitter voltage
is
less
than
500
mV
forward voltage
(or
reversed Was),
the
transistor
is
defective
4.
A
transistor
is
defective
if
its
base
current
is
larger
than 10
%
of
its
emitter current
(calculate
currents
from
voltage across
the base and
emit-
ter
series
resistors).
5. In
a
transistor differential pair (common
emitter
stages), either
their base voltages are the
same
in
normal
operating
condition,
or the
one
with
less
forward
voltage across
its
base
emitter
junction should be
off
(no
collector current);
otherwise,
one
of the transistors
is defective
6.3.2 Diode
A
diode (except a zener)
is
defective
if
there
is
greater
than one
volt
(typically
0.7
volt)
forward
voltage
across
it.
6.3.3 Operational Amplifier
1.
The
"
+
•• and
Inputs of
an
operational
amplifier
will
have
less
than 15
mV
voltage
dif-
ference when
operating under
normal
conditions.
2
When
the
output
of
the amplifier
Is
connoctod
to
the
"
- "
input (voltage follower
connection), the
output should be
the
same
voitago
as
the
"
+
"
input voltage;
otherwise, the operational ampli-
fier is defective
3
If
the
output voltage stays
at
maximum
positive,
the
"
+
"
input
voltage should bo moro
positive
than the
" -
"
input
voitago. or vice versa; other-
wise. the operational
amplifier
Is
defective.
6.3.4
FET
Translator
1
No
gate current
should be drawn
by
the
gate
of
an
FET
transistor.
If
so.
the transistor
is
defective
2
The
gate-to-source voltage
is
always revorse
biased under a normal operating
condition;
e g
.
the
source voltage
Is
more
positive than the
gate voltage
tor
2N5485.
and
the
source
voltage
is
more
negative than gate voltage
for
a 2N5462.
Otherwise, the FET
is
defective.
3
If
the
device supplying gate
voltage
to
an FET
saturates, the
FET has
too large a Vgs
(pinch
off)
for the Circuit and
should be
replaced
6.3.5
Capacitor
1
.
Shorted
capacitors
have zero
volts
across
their
terminals.
6-1