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Service Manual
Important Safety Notice
Special components are used in this projection television which are important for safety. These components are
identified on the schematic diagram by the symbol
and printed in BOLD TYPE on the replacement part list. It is
essential that these critical parts are replaced with the manufacturer’s specified replacement part to prevent x-ray
radiation, shock, fire or other hazards. Do not modify the original design without the manufacturer’s permission.
Safety Precautions
General Guidelines
An
isolation transformer
should always be used
during the servicing of a PTV whose chassis is not
isolated from AC power line. Use a transformer of
adequate power rating as this protects the technician
from accidents resulting in personal injury from
electrical shocks. It will also protect the PTV from being
damaged by accidental shorting that may occur
during servicing.
When servicing, observe the original lead dress,
especially in the high voltage circuit. Replace all
damaged parts (also parts that show signs of
overheating.)
Always replace protective devices, such as
fishpaper, isolation resistors and capacitors, and
shields after servicing the PTV. Use only
manufacturer’s recommended rating for fuses, circuits
breakers, etc.
High potentials, as high as 32kV, are present when this
PTV is operating. Operation of the PTV without the rear
cover introduces danger for electrical shock. Servicing
should not be performed by anyone who is not
thoroughly familiar with the necessary precautions
when servicing high-voltage equipment.
Extreme care should be practiced when handling the
picture tube
. Rough handling may cause it to implode
due to atmospheric pressure. (14.7 lbs. per sq. in.). Do
not nick or scratch the glass or subject it to any undue
pressure. When handling, use safety goggles and
heavy gloves for protection. Discharge the picture
tube by shorting the anode to chassis ground (not to
the cabinet or to other mounting hardware). When
discharging connect cold ground (i.e. DAG ground
lead) to the anode with a well insulated wire or use a
grounding probe.
X-ray Precautions
The front area (between the projection tube and the
lens) is enclosed by a metal box to ensure positive
safety during normal and abnormal conditions when
checking and repairing. To fully ensure safety, the
following precautions must be observed.
1.
Do not remove the lens or metal box.
2.
Make sure to turn the power OFF when the lens is
removed or when checking the cleanliness of the
lens.
3.
Do not remove the lens or metal box to check the
projection tube for operation by watching it directly.
Use a mirror or paper to view the image.
Before returning a serviced PTV to the owner, the
service technician must thoroughly test the unit to
ensure that is completely safe to operate. Do not use a
line isolation transformer when testing.
Leakage Current Cold Check
Unplug the AC cord and connect a jumper between the
two plug prongs. Press the POWER switch ON.
Measure the resistance between the jumpered AC plug
and expose metallic parts such as screw heads,
antenna terminals, control shafts, etc. If the exposed
metallic part has a return path to the chassis, the
reading should be between 240k
Ω
and 5.2M
Ω.
If the
exposed metallic part does not have a return path to
the chassis, the reading should be infinite.
Leakage Current Hot Check
(See Figure 1)
Plug the AC cord directly into the AC outlet. Do not use
an isolation transformer during the check.
Connect a 1.5k
Ω
10 watt resistor in parallel with a
0.15
µ
F capacitor between and exposed metallic part
and ground. Use earth ground, for example a
water pipe.
Using a DVM with a 1000 ohms/volt sensitivity or
higher, measure the AC potential across the resistor.
Repeat the procedure and measure the voltage
present with all other expose metallic parts.
Verify any potential does not exceed 0.75 volt RMS. A
leakage current tester (such a Simpson Model 229,
Sencore Model PR57 or equivalent) may be used in
the above procedure, in which case any current
measure must not exceed 1/2 milliamp. If any
measurement is out of the specified limits, there is a
possibility of a shock hazard and the PTV must be
repaired and rechecked before it is returned to
the customer.
Insulation Test
Connect an insulation tester between an exposed
metallic part and AC line.
Apply 1080VAC/60Hz for 1 second. Confirm that the
current measurement is 0.5mA ~ 2.0mA. Repeat test
with other metallic exposed parts.
X-ray Radiation
WARNING: The potential source of X-ray radiation in the
PTV is in the high voltage section and the picture tube.
Note: It is important to use an accurate, calibrated
high voltage meter.
Set brightness, picture, sharpness and color
controls to Minimum.
Measure the High Voltage. The high should be 31.5kV
± 1.0kV. If the upper limit is out of tolerance, immediate
service and correction is required to insure safe
operation and to prevent the possibility of premature
component failure.
0.15
µ
F
Figure 1. Hot Check Circuit
COLD
WATER
PIPE
(GROUND)
TO INSTRUMENT’S
EXPOSED METAL
PARTS
1500
Ω
,10W
AC VOLTMETER
