Quasar LP816 Service Manual - Important Safety Notice

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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