NAD T748 PROTECT

[Lynyrd]

Hello.
NAD T748 V1 Amplifier.

Turns on and immediately turns off after 3 seconds.Only NAD T748 on display.

Please let me know how protect mode works on this amp?
it's very difficult access to power transistors and before that, I would like to understand what signal comes on MCU in order to turn it off.
Where should voltage be measured?

REGARDS
SM
https://www.manualslib.com/manual/2171370/Nad-T748.html

 

[Lynyrd]

I have +12v on pin 21(protect) after power on.

 

[Lynyrd]

Its ok,it was 2 power transistors dead on left front channel.
I cut the legs,and Amplifier power on fine.
Thank you