Hi, I would like to share my experience...
So, I came across with common problem - no 50V on PSU 40-PF0750-PWD1G
L6566B was burned. Between pin 7 and GND were short circuit. I replaced L6566B with a new one, but it gave me nothing. However, it started if I touched pin 16 with multimeter probe. Obviously the protection is triggered.
If we look at the L6566B datasheet, we will see that to deactivate the protection (AC_OK), is enough to exceed 0.450 volts.
In my case, I have had 0.632 volts. This is enough at the first glance. But on the oscillogram on pin 16, I observed noise pulses an amplitude lower than 0.450 volts.
I guess the problem is in reducing the voltage of the PFC where I have 376 volts. The JBL PARTYBOX datasheet indicates that 390V plus/minus 4.5 percent is acceptable. In my case, 376 volts is in permissible limit.
Despite compliance with the parameters of the lower level, due to a decrease in the quality factor of the quenching capacitors, we have protection triggered.
My solution:
I replaced capacitors C32 and C36 with better ones.
I slightly changed the divider (R69,R78,R80/R87) to get a confident excess of the protection threshold. I set 1.1 volts.
There is another option to increase the PFC to 390 volts, but I left this option for you
))
I attached a scheme where I measured important voltages.
Good luck.
So, I came across with common problem - no 50V on PSU 40-PF0750-PWD1G
L6566B was burned. Between pin 7 and GND were short circuit. I replaced L6566B with a new one, but it gave me nothing. However, it started if I touched pin 16 with multimeter probe. Obviously the protection is triggered.
If we look at the L6566B datasheet, we will see that to deactivate the protection (AC_OK), is enough to exceed 0.450 volts.
In my case, I have had 0.632 volts. This is enough at the first glance. But on the oscillogram on pin 16, I observed noise pulses an amplitude lower than 0.450 volts.
I guess the problem is in reducing the voltage of the PFC where I have 376 volts. The JBL PARTYBOX datasheet indicates that 390V plus/minus 4.5 percent is acceptable. In my case, 376 volts is in permissible limit.
Despite compliance with the parameters of the lower level, due to a decrease in the quality factor of the quenching capacitors, we have protection triggered.
My solution:
I replaced capacitors C32 and C36 with better ones.
I slightly changed the divider (R69,R78,R80/R87) to get a confident excess of the protection threshold. I set 1.1 volts.
There is another option to increase the PFC to 390 volts, but I left this option for you
))I attached a scheme where I measured important voltages.
Good luck.
what did we say about hoarding too much stuff and depriving others of them?! *cough* socialism *cough* lol! 
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