HP 5254C - ASSEMBLY REPLACEMENT

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