Obviously, this example fault present output stage circuit. Voltage measurement field output block IC401 each foot, without exception, observe the IC welding feet around is full of rosin, estimate has been changed, doubt IC401 virtual welding, will IC401 feet rosin to remove excess rewelding again, commissioning is invalid. And will open a foot IC401 peripheral components one by one, welding test no abnormalities, concludes that the IC performance is bad, after the new change of commissioning, the fault is still. Fine voltage measuring IC401 each foot again, found 7 feet voltage fault have a small decline in volatility, the feet as power supply, by a small resistances R411 access, measuring R411 25 v into the terminal voltage is stable, doubt R411 bad performance. Remove the inspection, was found near the board side has a scorched black spots, measuring the resistance value is 1.5 Ω, only 0.3 Ω, will R411 change new commissioning, troubleshooting.nvqservice manual download site