axton c408 protect mode

Hello,
I have faulty Axton c408 amp and I need some help. One channel dead, on high current (car battery), PSU mosfets Q43;Q42 (FPQ50N06) burning. I figure out problem is not PSU. Without rear transistors Q211/Q213 and Q210/Q212 bad channel stops burning PSU Q43/Q42 mosfets. Now voltage +-35Volts ok. But channel still faulty anyway. So I did try figure out why this channel eat to much current. I did check all transistors seems they are ok no shorts. I have desolder Q216 and amp come in protect mode. Now I am getting none voltage on PSU at all. Okay I did solder back this Q216 and protect mode gone. But after 2-3 minutes testing faulty channel, protect mode comes again. Anyway there is no voltage on this channel because -+35v traces cut off. So now I believe something wrong with digital section wont turn on amp at all, protection mode. There is few chips NJM2068 (IC22A) and KA7500BD (IC21) they control this. Could some one explain how this section works? I have pdf these chips, I am confuse... Could some one spend few minutes and help me...
 

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