b2 6000w

Hi,
I have an issue with a repair,
I been told the amp works pretty good at cold winter days and not very good at summertime.
The issue is that it after a while of playing it cuts into protect, then starts working again, to be in protect again, and it goes faster frequency after the first time.
its been checked by a man referred from b2 to repair, without finding any fault.
I just checking if any encounter this problem before.
I was suspecting the ntc resistors but i used a heat gun and multimeter and the resistance goes down with increased heat. both side seems to be alike.
Any ide where to start ?
psu board, comparator circuit ? or bad MOSFET that heats more then others ?
best regards
Niklas.
 

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