2
20MR10
IMPORTANT SERVICE SAFETY PRECAUTION
Service work should be performed only by qualified service technicians who are thoroughly
familiar with all safety checks and the servicing guidelines which follow:
4A 125V
SER VICING OF HIGH VOLTAGE SYSTEM
AND PICTURE TUBE
When servicing the high voltage system,
remove the static charge by connecting a
10k ohm resistor in series with an insulated
wire (such as a test probe) between the pic-
ture tube ground and the anode lead. (AC
line cord should be disconnected from AC
outlet.)
1. Picture tube in this receiver employs integral
implosion protection.
2. Replace with tube of the same type number for
continued safety.
3. Do not lift
picture
tube
by the neck.
4. Handle the picture tube only when
wearing
shatterproof goggles and after discharging
the
high
voltage anode
completely
.
X-RADIATION AND HIGH VOLTAGE LIMITS
1. Be sure all service personnel are aware of
the
procedures and instructions covering X-radiation.
The only potential source of X-ray in current solid
state TV receivers is the
picture
tube. However, the
picture tube does not emit
measurable
X-Ray
radiation, if the high voltage is as specified in
the
"High Voltage Check" instructions.
It is only when high voltage is excessive that X-
radiation is capable of penetrating the shell of the
picture
tube
including
the lead in the glass material.
The important
precaution
is to keep the
high
voltage
below the
maximum
level specified.
2. It is essential that servicemen have available at all
times an accurate high voltage meter.
The calibration of this meter should be checked
periodically.
3. High
voltage should always be
kept
at the
rated
value
-no higher. Operation at higher voltages may
cause
a failure of the picture tube or high voltage circuitry
and; also,
under
certain conditions, may produce
radiation in exceeding of desirable levels.
4.
When the high voltage regulator is operating properly
there is no possibility of an X-radiation problem.
Every time a color chassis is serviced, the brightness
should be tested while
monitoring
the high
voltage
with a meter to be certain that the high voltage
does
not
exceed
the
specified
value
and
that
it
is
regulating
correctly.
5. Do not use a picture tube other than that specified
or make
unrecommended
circuit
modifications
to
the
high voltage circuitry.
6.
When
troubles hooting
and taking test
measurements
on a
receiver
with
excessive
high
voltage,
avoid being
unnecessarily close to the receiver.
Do
not
operate
the
receiver
longer
than
is
necessary
to locate the cause of
excessive
voltage.
WARNING
1. For continued safety, no
modification
of any circuit
should be attempted.
2. Disconnect AC power before servicing.
3. Semiconductor heat sinks are
potential
shock
hazards when the chassis is operating.
4. The chassis in this
receiver
has two
ground
systems
which are separated by
insulating
material.
The
non-
isolated (hot) ground system is for the B+
voltage
regulator
circuit
and
the
horizontal
output
circuit.
The
isolated
ground
system
is
for the low B+
DC
voltages
and the secondary
circuit
of
the
high
voltage
transformer
.
To prevent electrical shock use an
isolation
transformer between the line cord and power
receptacle, when servicing this chassis.
CAUTION: FOR CONTINUED
PROTECTION AGAINST A
RISK OF FIRE, REPLACE
ONLY WITH SAME TYPE 4A-
125V FUSE.
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