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BX—21511/1C-21351R
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Contents
Safety Precautions
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Safety Precautions
General Guide Lines
1.
It is advisable to insert an isolation transformer in the AC
supply before servicing a hot chassis.
2.
When servicing, observe the original lead dress in the high
voltage circuits. If a short circuit is found, replace all parts
which have been overheated or damaged by the short
circuit.
3.
After servicing, see that all the protective devices such as
insulation barriers, insulation papers, shields and isolation
R—C combinations are correctly installed.
4.
When the receiver is not being used for a long period of
time, unplug the power cord from the AC outlet.
5.
Potentials as high as 26.4Kv kV are present when this
receiver is in operation. Operation of the receiver without
the rear cover involves the danger of a shock hazard from
the receiver power supply. Servicing should
not be
attempted
by anyone
who
is not familiar with the
precautions necessary when working .on high voltage
equipment. Always discharge the anode of the picture to
the chassis before handling the tube.
6.
After servicing make the following leakage current checks
to prevent the customer from being exposed to shock
hazards.
Leakage Current Cold Check
1.
Unplug
the AC cord andconnect ajumper between thetwo
prongs of the plug.
Turn on the receiver's power switch.
Measure the resistance value with an ohmmeter, between
the jumpered AC plug and each exposed metallic cabinet
part on the receiver,
such
as screw
heads,
aerials ,
connectors, control shafts etc. When the exposed metallic
part has a return path to the chassis the reading should be
between 4M Q and 20M Q. When the exposed metal does
not have a return path to the chassis the reading must be
infinite.
Leakage Current Hot Check
1.
Plug the AC cord directly into the AC outlet. Do not use an
isolation transformer for this check.
2.
Connect a 2k ohm 10W resistor in series with an exposed
metallic part on the receiver and an earth such as a water
pipe.
3.
Use an AC voltmeter with high impedance to measure the
potential across the resistor.
4.
Check each exposed Metallic partand check
the voltage at
each point.
5.
Reverse the AC plug at the outlet and repeat each of the
above measurements.
6.
The potential at any point should not exceed 1.4 Vrms. In
case ameasurementis outside the limits specified, there is
a possibility of a shock hazard, and the receiver should be
repaired and rechecked
before it is returned to the
customer.
HOT CHECK CIRCUIT
A.C. Voltmeter
Water Pipe
exposed
metallic parts
2K ohm 10W
Fig.1
X—Radiation Warning
1.
The potential sources of X—Radiation in TV sets are the
high voltage section and the picture tube.
2.
Whenusingapicture tube testjig
for service ensure thatthe
jig is capable of handling 28.0 kV(21S1 Series) and 23kV
(14S1 Series) without causing X— Radiation.
NOTE : itis important to use an accurate periodically calibrated
high voltage meter
2
1.
Set the brightness to minimum.
2.
Measure the high voltage. The meter should indicate:—
26.4Kv + 1.5 kV (2181 Series)
21.5Kv + 1.5 kV (1481 Series)
ifthe meterindicationis out oftolerance, immediate service
and correction is required to prevent the possibility of
premature component failure.
3.
To prevent an X—Radiation possibility, itis essential to use
the specified tube.
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