Table of Contents
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Section
V
Model
5254C
a.
If
any reading
for
checks
1
thru
4 is
500
ohms,
there
is
a short circuit
in
the
mixer.
b.
If
checks
1
or
4
read
less
than
10K
the
diodes
are
defective.
c.
If
"infinity"
is
read
there
is
an open
circuit.
5-15.
VIDEO AMPLIFIER
ASSEMBLY
A5.
5-16.
A
faulty
video amplifier
circuit
can
usually be
detected by one
simple
check; short either
input,
base
of
A5Q1
or
A5Q2
to
ground and
the
amplifier should
oscillate
causing an increased
level indicator
meter
reading.
If
it
does
not
it
may
be
presumed
faulty.
Use
the
test
points
in
t
he
schematic diagram, Figure
8-6
and
the test points
and dc
voltages given
in
Troubleshooting
Aids,
Table
5-4.
5-17.
REPAIR
AND
REPLACEMENT.
5-18.
GENERAL.
5-19.
Paragraphs
5-20 through 5-35 are replacement
procedures
to
aid repair.
No
attempt should be
made
to
repair:
1)
the
Harmonic
Generator
A2;
2)
the
Har-
monic
Selector Cavity;
3)
the
Mixer
Assembly
A3, or
4)
the Filter
Assembly
A4.
These assemblies
should
be replaced as a
unit.
For
assistance contact
your
Hewlett-Packard
sales
and service
office.
5-20.
PRINTED
CIRCUIT
COMPONENT
REPLACEMENT.
5-21.
Component
lead holes
in
the
Model 5254C
cir-
cuit
boards have
plated walls
to
ensure good
electrical
contact
between conductors
on the opposite sides
of
the
board.
To
prevent
damage
to this
plating
and
to
the
replacement component,
apply heat sparingly and
work
carefully.
The
following
replacement procedure
is
recommended:
a.
Remove
defective
component.
b.
Melt
solder
in
component
lead
holes.
Use
clean
dry
soldering iron
to
remove
excess
solder.
Clean
holes with toothpick or
wooden
splinter.
Do
not
use
metal
tool for
cleaning as
this
may damage
through-
hole
plating.
c.
Bend
lead
of
replacement component
to the
cor-
rect
shape and
insert
component
leads
into
component
lead
holes.
Use
heat
and
solder sparingly, solder leads
in
place.
Heat
may
be applied
to
either side
of
board.
A
heat sink
(longnose
pliers,
commercial
heat -sink
tweezers,
etc)
should be
used
when
replacing transis-
tors
and diodes
in
order
to
prevent conduction
of
ex-
cessive heat
from
the
soldering iron
to
the
component.
d.
Through-hole
plating
breaks are
indicated
by
the
separation
from
the
board
of
the
round conductor pad
on
either side
of
the
board.
To
repair breaks,
press
conductor pads
against
board and
solder
replacement
component
lead
to
conductor pad on both sides
of
the
board.
5-22.
MULTIPLIER AMPLIFIER
ASSEMBLY
A1
.
5-23.
To remove
the
Multiplier
Amplifier
Assembly
A1
see
Figure
5-2 and
proceed
as
follows:
a.
Unscrew
the four
screws which
secure
left
side
plate
(MP7)
and
remove
left
side
plate.
b.
Unscrew
the four
screws which
secure
top
plate
(MP6)
and
remove
top
plate.
c.
Disconnect
the following
wires
from
Multiplier
Amplifier
Assembly A1
(see
Figure 8-2
):
From
red
P6(13)
violet
P6(15)
green
P6(50)
red
A5L14
violet
A5L15
d.
Disconnect black wire
to
meter from
ground
lug
on
MP14,
and
white
wire
to
meter from
capacitor
C3
and
MP14.
e.
Remove
screw
securing
aluminum
spacer
rod
(MP10)
to
plug-in guide
(MP9)
on
right side
of
instru-
ment.
Unscrew
spacer (MP10)
from
front panel.
f.
Remove
the
two screws
that
secure
amplifier
side plate
(MP12)
to
front panel.
g.
Remove
the
three
screws
that
mount machined
amplifier shield
(MP14)
and
slide shield to
rear and
out the right side to
clear
board
bracket
(MP13)from
Multiplier
Amplifier
Assembly
Al.
h.
Remove
the
two screws which secure
Multiplier
Amplifier
Assembly
to
Harmonic
Selector Cavity and
remove
assembly.
Note:
Harmonic
Generator As-
sembly
A2
is
mounted
to
bottom
of this
assembly.
i.
To
replace
this
assembly, reverse
the
procedure
used
in
steps a
through
h.
j.
All
replacement
Multiplier
Amplifier Assemblies
are adjusted
at
the
factory for
optimum
performance;
however,
if
a
general operation
check
is
desired, an
in-cabinet
performance
check
is
given
in
Table
5-4.
5-24.
HARMONIC
GENERATOR ASSEMBLY
A2.
5-25.
This
assembly
should be replaced as
a
unit
and
no attempt
made
to
repair
it.
To
remove
this
assembly
see
Figure 5-2 and proceed as
follows:
a.
Remove
Multiplier
Amplifier
Assembly
Al
as
described
in
Paragraph
5-22.
b.
Remove
the
two harmonic generator
mounting-
screws.
c.
Unsolder
capacitor
C25 from harmonic
genera-
tor
leads (see
Figure
8-2).
d.
Unsolder harmonic
generator leads
from As-
sembly Al
printed
circuit
board and
remove
harmonic
generator
(see
Figure
8-2).
e.
To
replace
this
assembly reverse
the
procedure
used
in
steps a
through
d.
5-2
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Table of Contents
Troubleshooting
