TU-PTA100E - Panasonic TV Service Manual (repair manual). Page 3

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An 

isolation transformer should always be used during the servicing of a receiver-decoder whose chassis is not isolated from 

the AC power line.  Use a transformer of adequate power rating to protect the technician from accidents resulting in personal 
injury from electrical shocks.  It will also protect the receiver-decoder from being damaged by accidental shorting that may occur 
during servicing.

When servicing, observe the original lead dress.  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-decoder.  Use only manufacturer’s recommended rating for fuses, circuits breakers, etc.

High potentials are present when this receiver-decoder is operating.  Operation of the receiver-decoder without the cover intro-
duces danger for electrical shock.  Servicing should not be performed by anyone who is not thoroughly familiar with the neces-
sary precautions when servicing high-voltage equipment.

Before returning a serviced receiver-decoder 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.

Unplug the AC cord and connect a jumper between the two plug prongs.

Measure the resistance between the jumpered AC plug and exposed metallic parts such as screwheads, antenna terminals, con-
trol shafts etc.  If the exposed metallic part has a return path to the chassis, the reading should be between 240 k

 and 5.2 M

.  

If the exposed metallic part does not have a return path to the chassis, the reading should be infinite.

Plug the AC cord directly into the AC outlet.  Do not use an isolation transformer during the check.

Connect a 1.5 k

, 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 expose metallic parts.

Verify that any potential does not exceed 0.75 Vrms.  A leakage current tester (such as a Simpson Model 299, Sencore Model 
PR57 or equivalent) may be used in the above procedure, in which case any current measured must not exceed 0.50 mA.  If any 
measurement is out of the specified limits, there is a possibility of a shock hazard and the receiver-decoder must be repaired and 
rechecked before it is returned to the customer.

Figure 1 : Hot Check Circuit

AC VOLTMETER

0.15

m

F

1500

W

, 10W

TO    INSTRUMENT'S

EXPOOSED   METAL

PARTS

COLD

WATER

PIPE

(GROUND)

Special components are used in this receiver-decoder which are important for safety.  These components are identi-
fied on the schematic diagram and on the replacement part list by the symbol

.  It is essential that these critical parts

are replaced with the manufacturer’s specified replacement part to prevent shock, fire or other hazards.  Do not mod-
ify the original design without the manufacturer’s permission.