Circuit Troubleshooting - Tektronix 545A Instruction Manual

Maintenance
—
Type
545A
Fig.
5-10. Converting the
power
transformer from
105-125
volt
operation
to
210-250
volt
operation.
operating condition.
If
the trouble
is still
apparent,
it
is
almost a
certainty that the oscilloscope
is
at
fault.
However,
should the trouble
appear
to
have been
corrected by
re-
placing the
plug-in unit,
the trouble
most
likely
lies
within
the original plug-in
unit
and
not with the oscilloscope.
Tube
failure
is
the
most prevalent cause
of circuit failure.
For
this
reason, the
first
step
in
troubleshooting
any
circuit
in
the instrument
is
to
check
for
defective tubes, preferably
by
direct substitution.
Do
not
depend
on tube
testers to
adequately
indicate the
suitability
of a tube
for
certain
positions within the instrument.
The
criterion for usability
of a tube
is
whether
or not
it
works
satisfactorily
in
the
instrument.
Be sure
to return
all
good
tubes
to their sockets;
if
this
procedure
is
followed
less
recalibration of the
instru-
ment
will
be required upon completion
of the servicing.
When
replacing
any
tube
in
the instrument,
check
first
to
see
that
components
through which
the tube
draws
current
have
not
been damaged. Shorted tubes
will
sometimes over-
load
and damage
plate-load
and
cathode
resistors.
These
damaged components
can generally
be
located by a
visual
inspection of the wiring.
If
no
damaged
components
are
apparent,
and
if
tube replacement does
not restore
opera-
tion,
it
will
be necessary
to
make
measurements
or
other
checks within the
circuit
to
locate the trouble.
The
component number
of
each
resistor,
inductor, capaci-
tor,
vacuum
tube, control
and
switch
is
shown
on
the
cir-
cuit
diagrams.
The following chart
lists
the
component num-
bers associated with
each
circuit:
All
numbers
less
than 100 Time-Base Trigger
100
series
Time-Base Generator
200
series
Time-Base Generator
B
300
series
Horizontal Amplifier
400
series
Delay
Pickoff
600
series
and
700
series
Low-Voltage
Power
Supply
800
series
CRT
Circuits
and
High-
Voltage
and Square-Wave
Calibrator
1000, 1100,
1200
series
.
Vertical Amplifier
1300
series
Delay
Line
Switch wafers
shown on
the
schematic diagrams are
coded
to
indicate the position of the
wafer on
the actual
switches.
The
number
portion of the
code
refers to
the
wafer number
on the switch assembly.
Wafers
are
num-
bered from
the front of the switch
to
the
rear.
The
letters
F
and
R indicate whether
the front or the rear of the
wafer
is
used
to
perform
the particular switching
function.
Photo-
graphic
details of these switches are
shown
on
the
same
fold-out
page
as
the
corresponding schematic diagram.
These photographs are provided
as
parts location guides.
CIRCUIT
TROUBLESHOOTING
Although
the
Type 545A
is
a
complex
instrument,
it
can
be thought
of
as consisting of eight
main
circuits,
in
addi-
tion
to the Calibrator
circuit.
These are
the:
1.
Low-Voltage
Power
Supply.
2.
CRT
Circuit
and High-Voltage
Power
Supply.
5-5