Wavetek 171 - Page 21

SECTION
V
TROUBLESHOOTING
6.1
FACTORY
REPAIR
Wavetek
maintains
a
factory repair
department
for those
customers
not
possessing
the necessary
personnel
or
test
equipment
to
maintain
the
instrument. If
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
TROUBLESHOOTING
CHART
Troubleshooting
charts
are
given
in figures
6-1
thru
6-4.
The
charts
do
not
cover every
possible trouble,
but will
be
an aid
in
systematically
isolating
faulty
components.
Figure 6-1.
Initial
Checks
Figure 6-2.
Generator
Mode
Checks
Sheet 1
Generator
Check
Sheet
2
Generator
Loop Check
Sheet
3 VCG Check
GCV
Check
TTL Check
Figure
6-3.
Power
Supply
Checks
Figure 6-4.
Synthesizer
Mode
Checks
Sheet
1
FA/ Check
Sheet
2
Synthesizer
Loop
Checks
Sheet
3 Synthesizer
Loop
Checks
Sheet
4 Frequency
Ranging
Check
Sheet
5 Generator
Phase
Lock
Loop
Check
Sheet
6 Reference
Selector
Check
6.3
TROUBLESHOOTING
INDIVIDUAL
COMPONENTS
6.3.1
Transistor
1.
A transistor
is
defective if
more
than one
volt
is
mea-
sured
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.
3. If
the
collector
and emitter voltages
are
the
same, but
tiie
base emitter voltage
is less than
500
mV
forward
voltage
(or
reversed
bias), 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
emitter
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
1.
A
diode is
defective if
there is
greater
than
one volt
(typically
0.7 volt) forward
voltage
across it
6.3.3
Operational
Amplifier
(e.g., UA741C,
LM318)
1.
The
“+"
and
"
inputs of
an
operational
amplifier
will have
less
than
15 mV voltage
difference
when
operating
under
normal
conditions.
2. If
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.
6.3.4
Capacitor
1.
Shorted
capacitors
have
zero
volts across
their termi-
nals.
2.
Opened
capacitor
can
be located
(but not always) by
using
a
good capacitor
connected
in
parallel
with the
capacitor
under
test and
observing the
resulting
effect.