2. A thermal cutout
switch is incorporated in
this
unit. If the
instrument has been
working but has
just
stopped, it may
have overheated and
tripped the ther-
mal
cutout switch.
The thermal
cutout
switch will
reset
itself when the interior temperature
of the instru-
ment
drops
to a safe value. Possible causes
of over-
heating
are: resffiction
oI
air circulation and
high
ambient
temperature.
3. If the
line voltage is within specifred limits, and
one
of the regulated power
supply output
voltages
is
not
correct, check that particular regulator circuit.
Each
of the regulated supplies is fused separately.
These
fuses should be checked and replaced if neces-
sary with
a
new
fuse of the
proper
value.
Note.'
Always
check the regulated voltages starting
with
the
-50-volt
supply and ending
with the
+200-
volt supply.
When
the circuit
ailment has been confined to a
Particular
regulator, then one may
kouble.shoot
within this circuit
to locate the
defective
compo-
nent
(s). The description
of the circuit involved
may
prove
useful when diagnosing circuit ailments.
4, If none
of
the regulated voltages
are
correct, then
the
trouble probably resides in the
-5O-volt
regulated
supply
since this
voltage
serves as a reference level for
the
other
three
regulated circuits.
One cause
of insufficient output
voltage is low un-
regulated dc voltage
which
might be caused by an
open
or shorted rectifier
diode.
5. If there is excessive ripple on any of the
unregu-
lated supplies,
replace the
frlter capacitor (s).
5.5. TROUBTE SHOOTING
THE CRT CIRCUIT
The
intensity, focus, geometry, and calibration o[
the cathode-ray
tube
display depend
on
proper opera-
tion
of the
high-vottage supply. To isolate
this
trouble,
remove
the rear cover from the
Main Frame. Measure
the voltage
at Test Point TPZDOI
using caution. This
voltage reading should be between
-1350
volts and
-
1440 volts with
respect
to
ground.
If
necessary, ad-
just
the HV ADJ potentiometer
R2009R for proper
voltage.
Remove power and
measur€ the resistance of
the primary
and secondary
windings
of
high-voltage
transformer T2001. The resistance across
the primary
winding
should measure around 5 ohms.
Nleasure the
resistance
of the secondary winding
from the anode of
CR2052 to ground; it should measure
around 175
ohms.
Also, measure the voltages at other
points in the
circuit
for
which
typical values are
given on the high-
voltage
power supply schematic.
If all
of
these voltages
check
out correctly, then the
trouble may reside with
the cathode-ray tube itself which should be checked.
If the low-voltage power supply
is
operating
nor-
mally, but no spot
or
trace is visible on
the
screen,
then
the trouble
might be
a
defective cathode-ray tube,
a
defect in the CRT circuitry including the high-
mointenonce
qnd
recolibrotion-section
5
sory
is available
and
permits
the
plug-in unit to
be
operated
while
extended through
the front of
the
oscil
loscope.
7.
If
rouble is isolated
to one of
the plug-in
units,
refer
to the appropriate module manuals for
further
information. If
the trouble has been definitely
isolated
to the Main Frame
or
Indicator, then
proceed as
follows:
The first
step in rouble shooting the
Indicator Unit
is to measure
the
power supply voltages at
Test
Points TPl50l, TPl2Ol, TPll0l and TPlOOl
lo-
cated
on
the
Main Frame, If all of
the voltages are
not
as i4dicated, the rouble
is
in
the low-voltage
power
supply or the power source. To
check
these,
refer
to the subsequent
paragraph entitled "Trouble
Shooting
the
Power Supply." If all thqse
voltages are
proper,
the trouble resides in the
cathode-ray tube
circuit. In this instance,
refer to
the
paragraph
en-
titled "Trouble
Shooting
the Cathode-Ray
Tube
Circuit" in this Section of the manual,
5.5. TROUBTE SHOOTING
THE POWEN
SUPPIY
.
WARNING
WHEN THE COVERS ARE REMOVED
FROM
THE INSTRUMENT
FOR SERVICING, EX-
ERCISE
CAUTION WHILE
THE POWER IS
ON.
The lower-voltage busses are
potentially
more
dangerous than the cathode-ray
tube poten-
tial
because o[ the high-current capabilities
and
large filter
capacitors employed
in
these supplies.
When you
reach
into
the
instrirment with one
hand
while
it is
turned on,
do not grasp the
metal frame
with
the
other
hand. If
possible,
stand
on
an insulated floor and
use insulated
tools. It is advisable to ground the
third lead
in
rhe
power cord whenever the instrument
is
in use.
As an aid in uouble shooting
the
power supply,
refer
to the
{unctional block diagrams
Figures 3-l and
3-2, and to the
low-voltage power supply schematic.
L If
the
insrument fails to operate,
includinB the
pilot
light,
checl
the source of
power and
determine
that the power cord is firmly in place. Then
check
fuses located
at the
rear
of
the instrument.
(See
Figure
5-2.)
Nor€.'
Disconnect the power cord when working
on
the
uanslormer Tl00l and associated
circuits.
If the fuse is blown, replace it with one ol
the
proper
value
and
reconnect the line cord. If the new
fuse
blows,
immediately
check
the power transformer
for
shorted primary
or
secondary
windings. Shorted
rectifiers
i! the secondary
circuit will also blow the
line
fuse Fl0l. Check for an operr
primary winding
of Tl00l if the line-fuse
is good.
5-3