Sylvania LC420SS8 Service Manual page 53

Inverter Power CBA Bottom View
NOTE:
The voltage for parts in hot circuit is measured using
hot GND as a common terminal.
Because a hot chassis ground is present in the power
supply circuit, an isolation transformer must be used.
Also, in order to have the ability to increase the input
slowly,when troubleshooting this type power supply
circuit, a variable isolation transformer is required.
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BA81H0F01022-4