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HP 120A - Sweep Generator; Maintenance; Introduction; Removing the Cabinet

HP 120A
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Sect.
IV
Page
1
SECTION
IV
MAINTENANCE
Adjustments
and
voltages
referred
to
in
this
maintenance
section
are
intended
for
maintenance
purposes
only
and
are
not
intended
to
be
in
terpreted
as
specifications.
4-1
INTRODUCTION
This
section
contains
instructions
for
adjusting
and
servicing
the
Model
120A
Oscilloscope,
Components
of
the
Model
120A
are
readily
accessible
by
remov
ing
the
instrument
from
the
cabinet.
All
tubes
and
transistors
are
removeable
from
above
the
chassis
while
other
individual
components
are
easily
reached
from
below
the
chassis.
Conventional
point-to-point
wiring
is
used
throughout
so
that
the
Model
120A
may
be
easily
repaired
with
only
the
minimum
of
tools.
Whenever
possible
standard,
readily
obtainable,
com
ponents
have
been
used.
Other
special
components
may
be
obtained
directly
from
the
Hewlett-Packard
Company.
When
ordering
directly
from
($)
be
sure
to
specify
model
and
serial
number
of
instrument
and
description
of
component
as
given
in
table
of
re
placeable
parts
together
with
the
stock
number.
In
general,
sections
in
the
Model
120A
will
be
found
behind
the
controls
for
that
section
on
the
front
panel.
The
power
supplies
are
in
the
rear;
the
low
voltage
on
top
of
the
chassis
and
the
high
voltage
in
the
shielded
box
underneath
and
the
transistor-regulated
filament
supply
on
the
upper
chassis
brace.
Controls
and
tubes
are
marked
on
the
chassis.
The
material
in
this
section
is
divided
according
to
circuit
func
tions,
each
section
having
a
complete
set
of
adjust
ment
instructions
and,
at
the
rear
of
the
manual,
a
schematic
and
a
voltage-resistance
diagram.
The
material
in
this
section
is
as
follows:
4-2
Removing
the
Cabinet.
4-3
Connecting
for
230-volt
Power
Lines.
4-4
Tube
Replacement.
4-5
Isolating
Troubles
to
Major
Sections.
4-6
Adjustment
Procedure.
4-7
Turn
On.
4-8
Power
Supplies.
4-9
Trigger
Generator.
4-10
Vertical
Amplifier.
4-11
Horizontal
Amplifier.
4-12
Sweep
Generator.
4-2
REMOVING
THE
CABINET
First,
remove
the
power
cord
from
the
wall
recepta
cle.
Remove
the
two
large
screws
at
the
rear
of
the
cabinet.
Do
not
remove
any
screws
from
the
front
panel.
Push
the
instrument
from
the
cabinet
by
push
ing
the
rear
of
the
chassis
through
the
power
cord
hatch
at
the
rear
of
the
instrument.
Now
slide
the
in
strument
from
the
cabinet
by
pulling
forward.
Pull
the
power
cord
through
hole
in
the
cabinet.
The
instrument
will
now
be
completely
free
for
servicing.
CAUTION
When
the
cabinet
is
removed,
dangerous
voltages
are
exposed.
Take
adequate
safety
precautions,
especially
when
working
around
the
CRT
terminals
and
power
supplies.
4-3
CONNECTING
FOR
230-VOLT
POWER
LINES
The
120A
is
normally
shipped
from
the
factory
with
the
dual
primary
of
the
power
transformer
windings
connected
in
parallel
for
use
on
115-volt
ac
lines,
un
less
otherwise
specified
on
the
order.
The
windings
can
easily
be
reconnected
in
series
for
use
on
230-
volt
power,
if
desired.
First
find
the
power
supply
input
terminal
strip
located
next
to
the
power
trans
former.
Notice
that
the
two
outer
terminals
on
each
side
are
jumpered
together,
connecting
the
windings
in
parallel.
Remove
these
jumpers
and
connect
an
in
sulated
jumper
between
the
second
and
fourth
termi
nals,
connecting
the
windings
in
series.
Do
not
at
tempt
to
use
this
instrument
on
any
voltage
direct

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