Sony Trinitron PVM-1271Q Service Manual page 3

SAFETY CHECK-OUT
PVM-12710\
After correcting the original service
problem,
perform the following safety checks before releasing
the set to the
customer:
1
.
Check
the area of your
repair for
unsoldered or
poorly-soldered connections.
Check
the entire
board
surface for solder splashes
and
bridges.
2.
Check
the interboard wiring
to
ensure that
no
wires
are
"pinched"
or contact
high-wattage
resistors.
3.
Check
that
all
control knobs,
shields,
covers,
ground
straps,
and
mounting hardware have
been
replaced.
Be
absolutely certain that
you
have
replaced
all
the insulators.
4.
Look
for
unauthorized replacement
parts, par-
ticularly transistors, that
were
installed
during
a
previous
repair.
Point
them
out
to
the
customer
and
recommend
their
replacement.
5.
Look
for parts which,
though
functioning,
show
obvious
signs
of deterioration. Point
them out
to
the customer and
recommend
their replace-
ment.
6.
Check
the
line
cord
for
cracks
and
abrasion.
Recommend
the
replacement
of
any such
line
cord to the customer.
7.
Check
the condition of
the
monopole
antenna
(if
any).
Make
sure the end
is
not
broken
off,
and has
the
plastic
cap on
it.
Point out the danger of
impalement on
a
broken antenna
to
the
customer, and
recommend
the
antenna's
replacement.
8.
Check
the
B+
and
HV
to see
they
are at
the
values specified.
Make
sure
your instruments
are accurate; be suspicious of
your
HV
meter
if
sets
always have low
HV.
9.
Check
the antenna terminals,
metal
trim,
"metallized"
knobs, screws,
and
all
other
exposed metal
parts for
AC
leakage.
Check
leakage
as described
below.
To Exposed Meta!
Parts
on
Set
0.1 5
pF
AC
voltmeter
10.75 V)
Earth
Ground
\Fig.
A. Using an
AC
voltmeter
to
check
AC
leakage.
LEAKAGE
TEST
The
AC
leakage from any exposed metal
part to
earth
ground and from
all
exposed metal
parts to any
exposed metal
part having
a
return
to chassis,
must
not
exceed
0.5
mA
(500 microampers). Leakage
current can be measured by any one
of three
methods.
1
.
A
commercial
leakage
tester,
such
as
the
Simpson 229
or
RCA
WT-540A.
Follow
the
manufacturers'
instructions to use these
instru-
ments.
2.
A
battery-operated
AC
milliammeter. The
Data
Precision 245
digital
multimeter
is
suitable for
this
job.
3.
Measuring
the voltage
drop
across
a resistor
by
means
of
a
VOM
or battery-operated AC'volt-
meter.
The
"limit" indication
is
0.75 V,
so
analog meters must have
an accurate low-
voltage
scale.
The Simpson 250
and
Sanwa
SH-63Trd
are
examples
of
a
passive
VOM
that
is
suitable.
Nearly
all
battery operated
digital
multimeters
that
have
a
2V AC
range
are
suitable.
(See
Fig.
A)
HOW
TO
FIND
A
GOOD
EARTH GROUND
A
cold-water pipe
is
guaranteed
earth ground; the
cover-plate retaining screw
on most
AC
outlet
boxes
is
also
at
earth ground.
If
the retaining screw
is
to
be
used
as
your earth-^ound,
verify that
it is
at
ground
by measuring
the resistance
between
it
and
a cold-
water pipe with an ohmmeter. The
reading should be
zero
ohms.
If
a
cold-water pipe
is
not
accessible,
connect
a
60—100
watts trouble
light (not a
neon
lamp) between
the hot
side
of the receptacle and
the
retaining screw.
Try both
slots, if
necessary,
to locate
the hot
side
of the
line,
the
lamp
should
light at
normal
brilliance
if
the
screw
is
at
ground
potential.
(See
Fig. B)
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