Panasonic CT-27SL13MUG, Service Manual, Page: 3 / 149

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 wellinsulated 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 shieldlimits 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 50kV without causing
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 A.C. 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. If the exposed metallic part has a returnpath to the
chassis, the reading should be between 240k and 5.2M . 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 1.5k 10 watt resistor in parallel with a 0.15 F 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 0.5 milliamp. Ifany 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.
Hot check circuit
3