I was working on y medical ventilator, i have assembled everything and it was working than i delivered it to costumer, after 1 week my costumer called me and said that when he start calibrating o2 it says error may be o2 sensor not working. Than i got the ventilator back and i start trouble shooting i replaced the o2 sensor and same problem exist. It means there is a problem in a main board and i need to change the board. But the thing is that i really dont understand how could be board demage even i test and run the machine for 24 hours and the flow sensor is also ok. Can anybody tell me the reason what thing could demage the board and why only flow sensor.