1 Safety Precautions
An isolation transformer should always be used during the servicing ofa 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
When servicing, observe the original lead dress. Replace all damaged parts (also parts that show signs ofoverheating.)
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 ofthe receiver-decoder without the 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.
Before returninga 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.
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 exposed metallic parts such as screwheads, antenna terminals, control
shafts etc. Ifthe exposed metallic part has a return path to the chassis, the reading should be between 240 kW and 5.2 MW. Ifthe
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 1.5 kW, 10 watt resistor in parallel with a 0.15 mF 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. Ifany
measurement is out ofthe specified limits, there is a possibility ofa shock hazard and the receiver-decoder must be repaired and
rechecked before it is returned to the customer.
Figure 1: Hot Check Circuit