Hi,
Okay, does this power supply use a mechanical switch for On/Off.
PL811 is the two pin (red) socket used for this connection. If so, the switch is normally SHORT circuit when OFF, and OPEN circuit when switched ON, and there won't be any 5V standby voltage until it is switched on.
If it doesn't use this, there should 325v on the main smoother capacitor, all the time the set is plugged in, if not, check your AC input, bridge rectifier, etc.
Regards,
John