Service
Model 182C
8-38.
Troubleshooting the low voltage
$upply isfacilitated
by removing the power supply from the oscilloscope. This
will provide access to the power transformer, rectifiers
and
filters.
Removing
the
module also disconnects the
power supply from all other circuits of the oscilloscope,
thus confining the troubleshooting effort to the
low
voltage supply. The procedure for removing the
power
supply module is explained later in this section of the
manual.
Lethal
voltages
are
exposed when the
power supply module is operated
out-
side the oscilloscope mainframe.
8-39.
The
low
voltage power module
can be powered
from the oscilloscope mainframe
by using the Model
10133A Service Extender. This provides line voltage
power
to
the module while continuing to control it by
the front-panel power LINE switch. The extender does
not
connect dc operating power to the oscilloscope main-
frame.
This
permits
troubleshooting the low voltage
supplies with no
external
circuit loads.
8-40.
The
-rlOOV supply should be checked first,
since
all other supplies use it as
a reference. Unregulated oper-
ation
of all of the other supplies may be
the result of
a
defective +100V supply. Use
the convenient test points to
monitor the regulated output
of
a supply.
If the
-MOOV
supply is
defective, verify operation of the reference supply
which
is
regulated by the 9-volt zener diode.
8-41.
HIGH VOLTAGE POWER SUPPLY AND
REGULATOR.
WARNING
^
Lethal voltages are exposed when the
oscilloscope is turned on
with the high
voltage
power
supply cover removed.
8-42. High-voltage
power supply problems
are usually
in-
dicated by no display,
a display that is too bright,
an
arcing
sound, slow trace shift or hlooming
or sudden shifts in
display intensity.
Regulator problems may
result in no
high-voltage
or excessive high-voltage.
8-43. If
only one high voltage
output is missing, check
the appropriate rectifier and filter
circuit. If high
voltage
is present but not properly
adjustable, refer
to the high
voltage troubleshooting
tables (Tables 8-7
and 8-8).
The CRT post accelerator
lead may
have a high
voltage present even if the
instrument
has been turned off for
a
long time. Ground
both CRT and H.V.
Multiplier
connections to discharge.
The
CRT post
accelerator
lead may
have a high voltage present even if the
instrument
has been turned
off
for a
long time. Ground both CRT and H.V.
Multiplier connections to discharge.
8-44.
If no high voltage is
present, check
the
high
voltage
oscillator circuitry. The oscillator supply voltage,
unregulated
-I-27V.
is fused by
F3
on the Regulator
assembly. The oscillator frequency isapproximately40KHz.
With the High Voltage
Multiplier
output
disconnected,
(by
disconnecting the CRT post-accelerator lead}, the
oscillator
frequency
should
increase
to
approximately
50
kHz.
8-45.
The CRT cathode
and grid high voltage leads can be
disconnected
by
removing
the
CRT socket. This will
further
isolate the
trouble. If
it is determined
that the
H.V.
Multiplier
is
faulty,
it
must be replaced
as a complete
unit, since
it is a sealed
assembly.
8-46.
DISASSEMBLY
INFORMATION.
8-47. If it is necessary to remove an assembly for
servicing
or replacement,
the following
information
will provide
guidance
in accomplishing
this
in a manner to
prevent
damage
and facilitate removal
and replacement.
8-48.
The instrument
has been designed
to readily
permit
disassembly tor
component
removal, troubleshooting
or
replacement.
Each module
is a plug-in
type, and may
be
removed
without unsoldering
any connections.
Single or
multi-contact
connectors are
used throughout for signal,
control
and operating
power connections.
»49. COVER REMOVAL.
8-50.
The instrument has
a
two-piece
cover. Remove
the
covers as follows:
a. Ensure that LINE ptower switch is OFF and dis-
connect power plug from line power source.
b. Set
oscilloscope
on
rear
end.
c.
Release the
3
quarter-turn fasteners
located on each
side
of the instrument. The cover retainers will be
com
pletely
free. Figure
8-2
shows the location
of
the
fasteners.
d. Loosen 2
captive screws
located on
handle ends.
e.
Remove top cover
by
expanding slightly and pulling
away from instrument.
f.
Remove bottom
cover
by
extending tilt stand,
expanding arrd
pulling away from instrument.
g.
Return instrument
to horizontal position and remove
rear
access cover by releasing single quarter
turn
fastener.
8-4
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