29A-80ST
29A-90ST
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:
WARNINGX-RADIATION AND HIGH VOLTAGE LIMITS
1. For continued safety, no modification of any circuit1. Be sure all service personnel are aware of the
should be attempted.procedures and instructions covering X-radiation. The
2. Disconnect AC power before servicing.only potential source of X-ray in current solid state
3. Semiconductor heat sinks are potential shockTV receivers is the picture tube. However, the picture
hazards when the chassis is operating.tube does not emit measurable X-Ray radiation, if
4. The chassis in this receiver has two ground systemsthe high voltage is as specified in the "High Voltage
which are separated by insulating material. The non-Check" instructions.
isolated (hot) ground system is for the +B voltageIt is only when high voltage is excessive that X-
regulator circuit and the horizontal output circuit. radiation is capable of penetrating the shell of theThe
isolated ground system is for the low +B DC voltagespicture tube including the lead in the glass material.
and the secondary circuit of the high voltageThe important precaution is to keep the high voltage
transformer.below the maximum level specified.
To prevent electrical shock use an isolation2. It is essential that servicemen have available at all
transformer between the line cord and powertimes an accurate high voltage meter.
receptacle, when servicing this chassis.The calibration of this meter should be checked
periodically.
SERVICING OF HIGH VOLTAGE SYSTEM3. High voltage should always be kept at the rated value
-no higher. Operation at higher voltages may cause
AND PICTURE TUBE
a failure of the picture tube or high voltage circuitry
When servicing the high voltage system,and;also, under certain conditions, may produce
radiation in exceeding of desirable levels.
remove the static charge by connecting a
4. When the high voltage regulator is operating properly
10k ohm resistor in series with an insulated
there is no possibility of an X-radiation problem. Every
wire (such as a test probe) between the pic-
time a colour chassis is serviced, the brightness
ture tube ground and the anode lead. (ACshould be tested while monitoring the high voltage
line cord should be disconnected from ACwith a meter to be certain that the high voltage does
not exceed the specified value and that it is regulating
outlet.)
correctly.
1. Picture tube in this receiver employs integral5. Do not use a picture tube other than that specified or
implosion protection.
make unrecommended circuit modifications to the
2. Replace with tube of the same type number for
high voltage circuitry.
continued safety.6. When trouble shooting and taking test measurements
3. Do not lift picture tube by the neck.
on a receiver with excessive high voltage, avoid being
4. Handle the picture tube only when wearing
unnecessarily close to the receiver.
shatterproof goggles and after discharging the highDo not operate the receiver longer than is necessary
voltage anode completely.
to locate the cause of excessive voltage.
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ACEC
SHARP
