Sharp 50NP4 Service Manual page 2

Service work should be performed only by qualified service technicians who are throughly familiar with all
safety checks and the servicing guidelines which follow:
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 shcok hazards when
the chassis is operating.
4. The chassis in this receiver has two ground systems which are
separated by insulating material.
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 receptable, when servicing
this chassis.
CAUTION: FOR CONTINUED
PROTECTION AGAINST A
F
RISK OF FIRE, REPLACE
ONLY WITH SAME TYPE 4A-
4A 125V
125V FUSE.
SERVICING 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 picture
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.
IMPORTANT SERVICE SAFETY PRECAUTION
The non-isolated (hot)
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 ÒHigh
Voltage CheckÓ instructions.
It is only when high voltage is excessive that X-radiation is
capable of penetrating the shell of the picture tuve including
the lead in the glass material. The important precaution is to
keep the high voltage below the maximum level specified.
2. Is 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 volate circuity 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 trouble shooting and taking test measurements on a
receiver with excessive
unnecessarily close to the receiver.
Do not operate the receiver longer than is necessary to locate
the cause of excessive voltage.
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high voltage, avoid being