Panasonic PV-4601 A Service Manual page 116

Fig. E3
Cautions:
Use an Isolation Transformer (Variable)
Because a Hot Chassis Ground is present in the Switched Mode Power Supply
Circuit, an Isolation Transformer must be used. Also, in order to have the ability to
increase the input voltage slowly, when troubleshooting this type of Power Supply
Circuit, a variable Isolation Transformer is required.
116