After troubleshooting found open R11 10 ohm resistor on power supply board.
Problem solved by component replacement.
Technical pluses – simplicity , perfect components management on all boards, extremely high output power per channel in range 180- 250 W , good heath sink management, ability to use it as commercial unit for big audience like stadiums, schools and more, easy to set up, good attention to rectifier section and DC voltage quality .
Technical minuses – connections between power board and big filter capacitors relying on bolts only ( oxidation sensitive unit ), sensitive for AC 117v input voltage, no real protection circuit inside, high frequency response in reality is low ( on frequency 10-19 kHz), missing ability to control gain and volume on front panel , high demands for quality speakers, speaker wires and input audio signal . All modules inside and power transformer not shielded. Zero attention to AC line interference .