When I connect my MP566 to power, first everything seems normal. I have 223V between 0V and TP2, -5V between 0V and TP8. However, when connecting a 1 VAC sine wave to the input the LED stays off when turning P1 to Max (it stays off as well when turning P2 to Max). I constantly have 0VAC between 0V and TP4, only when moving P1 the value shortly rises, but breaks down to 0VAC immediately.

I already double checked all the solder joints, nothing seems wrong there... any ideas how to find the error?