Panasonic CT-20R6E Service Manual page 2

Special components are used in this television set which are important for safety. These parts are identified on the
schematic diagram by the symbol
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.
General Guidelines
An Isolation Transformer should always be used during
the servicing of a receiver 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 Receiver 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 Receiver. Use only manufacturer's
recommended rating for fuses, circuits breakers, etc.
High potentials are present when this Receiver is
operating. Operation of the Receiver 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.
Avoid prolonged exposure at close range to unshielded
areas of the picture tube to prevent exposure to
X-ray radiation.
The Test Picture Tube used for servicing the chassis at
the bench should incorporate safety glass and
magnetic shielding. The safety glass provide shielding
for the tube viewing area against X-ray radiation as
well as implosion. The magnetic shield limits the X-ray
radiation around the bell of the picture tube in addition
to the restricting magnetic effects. When using a
picture tube test jig for service, ensure that the jig is
capable of handling
X-ray radiation.
Before returning a serviced receiver 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.
Measure the resistance between the jumpered AC plug
and expose metallic parts such as screwheads,
antenna terminals, control shafts, etc.
Important Safety Notice
and printed in BOLD TYPE on the replacement part list. It is essential that
Safety Precautions
35kV without causing
If the exposed metallic part has a return path to the
chassis, the reading should be between 240kΩ and
5.2MΩ. If the exposed metallic part does not have a
return path to the chassis, the reading should be
infinite.
Leakage Current Hot Check
Plug the AC cord directly into the AC outlet. Do not use
an isolation transformer during the check.
Connect a 1.5kΩ 10 watt resistor in parallel with a
0.15µF capacitor between an 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 exposed metallic parts.
Verify that 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 Receiver must be
repaired and rechecked before it is returned to the
customer.
AC VOLTMETER
TO
INSTRUMENT'S
EXPOSED METAL
PARTS
X-ray Radiation
WARNING: The potential source of X-ray radiation in the
TV set are the High Voltage section and the picture tube.
Refer to X-RAY PROTECTON CIRCUIT CHECK in
Service Notes in this manual to confirm HHS Voltage.
High Voltage (CRT Anode)
Confirm Anode voltage is within limits:
Set the BRIGHTNESS, PICTURE, SHARPNESS and
COLOR to minimum (To obtain a dark image). Measure
High Voltage. It should be:
26.60±1.25kV for CT-20R6E/CE, CT-20G6E/DE,
and 27.70±1.25kV for CT-2016SE,
CT-2006SE, CT-20D11E/DE
If the upper limit is out of tolerance, immediate service
and correction is required.
Note: It is important to use an accurate, calibrated
high voltage meter.
- 2 -
(Fig. 1)
COLD
WATER
PIPE
(GROUND)
0.15µF
1500Ω,10 W
Figure 1. Hot Check Circuit
.