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Safety Precautions
General Guidelines
1.
It is advisable to insert an isolation transformer in the AC
power line before servicing a hot chassis.
power line before servicing a hot chassis.
2.
When servicing, observe the original lead dress, espe-
cially the lead dress in the high voltage circuits. If a
short circuit is found, replace all parts which have been
overheated or damaged by the short circuit.
cially the lead dress in the high voltage circuits. If a
short circuit is found, replace all parts which have been
overheated or damaged by the short circuit.
3.
After servicing, see to it that all the protective devices
such as insulation barriers, insulation papers, shields,
and isolation R-C combinations, are properly installed.
such as insulation barriers, insulation papers, shields,
and isolation R-C combinations, are properly installed.
4.
Before switching the power on, measure the resistance
between B+ line and cold side chassis ground. Connect
the “-” side of an ohmmeter to the B+ line, and the “+”
side to chassis ground. Each line must have more resis-
tance value than the specified one as follows:
between B+ line and cold side chassis ground. Connect
the “-” side of an ohmmeter to the B+ line, and the “+”
side to chassis ground. Each line must have more resis-
tance value than the specified one as follows:
5.
When the set is not used for a long period of time,
unplug the AC power cord plug from the AC line outlet.
unplug the AC power cord plug from the AC line outlet.
6.
High voltage points, as high as 33 ± 1.0 kV, are present
when the set is in operation. Operating the set without
the rear cover involves in a dangerous electrical shock
from the set power supply. Servicing must not be
attempted by anyone who is not thoroughly familiar with
the necessary precautions when working on high volt-
age equipment. Always discharge the anode of the pic-
ture tube to chassis ground before handling the picture
tube.
when the set is in operation. Operating the set without
the rear cover involves in a dangerous electrical shock
from the set power supply. Servicing must not be
attempted by anyone who is not thoroughly familiar with
the necessary precautions when working on high volt-
age equipment. Always discharge the anode of the pic-
ture tube to chassis ground before handling the picture
tube.
7.
After servicing, make the following leakage current
checks to prevent the customer from dangerous electri-
cal shock.
checks to prevent the customer from dangerous electri-
cal shock.
Leakage Current Cold Check
1.
Unplug the AC power cord and short between the two
prongs of the AC plug with a jumper wire.
prongs of the AC plug with a jumper wire.
2.
Set the power switch of this set to ON position.
3.
Measure the resistance value with an ohmmeter
between the shorted AC plug and each exposed metallic
part of the set cabinet such as screwheads, connectors,
and control shafts. When the exposed metallic part has
a return path to the chassis, the reading should be more
than 1 M
between the shorted AC plug and each exposed metallic
part of the set cabinet such as screwheads, connectors,
and control shafts. When the exposed metallic part has
a return path to the chassis, the reading should be more
than 1 M
.
When the exposed metal part does not have a return
path to the chassis, the reading must be infinity.
path to the chassis, the reading must be infinity.
Leakage Current Hot Check (See Fig.1)
1.
Plug the AC power cord directly into the AC line outlet.
Do not use an isolation transformer for this check.
Do not use an isolation transformer for this check.
2.
Connect a 1.5k
, 10W resistor, in parallel with a 0.15µF
capacitor between each exposed metallic part of the set
and an earth ground such as a water pipe.
and an earth ground such as a water pipe.
3.
Use a high impedance AC voltage meter to measure the
voltage across the resistor.
voltage across the resistor.
4.
Measure the voltage at each exposed metallic part.
5.
Reverse the AC plug inserting direction at the AC line
outlet and repeat each of the above measurements.
outlet and repeat each of the above measurements.
6.
The voltage at any point must be less than 0.75Vrms.
7.
A leakage current tester (Symptom Model 229 or the
equivalent) may be used to make the hot checks. In this
case, the current must be less than 500µA.
equivalent) may be used to make the hot checks. In this
case, the current must be less than 500µA.
8.
If the reading is more than the above value, the set must
be repaired and rechecked before it is returned to the
customer because of a possibility of an electrical shock.
be repaired and rechecked before it is returned to the
customer because of a possibility of an electrical shock.
X-Radiation
Warning:
1.
The potential sources of X-Radiation in the monitor set
are the high voltage section and picture tube.
are the high voltage section and picture tube.
2.
When using a picture tube test jig for service, make sure
that jig is capable of handling 32.5kV without causing X-
Radiation.
that jig is capable of handling 32.5kV without causing X-
Radiation.
3.
For continued X-radiation protection, in case that at least
one of the components listed below is replaced, follow
the adjustment procedure of the high voltage circuit.
Precise adjustment is necessary for R720 to protect X-
Radiation. Refer to “High Voltage and X-Radiation Pro-
tective Circuit Adjustment section”.
one of the components listed below is replaced, follow
the adjustment procedure of the high voltage circuit.
Precise adjustment is necessary for R720 to protect X-
Radiation. Refer to “High Voltage and X-Radiation Pro-
tective Circuit Adjustment section”.
T551, IC457, IC5508, D512, R520, R521, R522, R809,
R810, R5568, C481, C528, RL001
R810, R5568, C481, C528, RL001
B+ line
Minimum Resistance
220V(TPD7)
10k
144V(TPD17)
10k
23V(TPD25,33)
3k
15V(TPD20)
5k
12V(TPD23)
50k
Hot-Check Circuit
Fig. 1
AC Voltmeter
To
Instrument’s
Exposed
Metallic Parts
Instrument’s
Exposed
Metallic Parts
1.5k
, 10W
0.15
µ
F
Water Pipe
( Earth )
( Earth )
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