Ok. So I replaced the damaged DHT22 and wired a separate 0v for the 5v electronics. I tested without venting cycle as this was when pop happened. It functioned apart from no humidity reading from front sensor (reads 1.0 constantly), must have been damaged when other melted, temperature appeared in line with new sensor. I tried venting cycle and immediately servo was struggling so I switched off. The 5v supply is supposed to be 800mA and it is powering two DHT22, the relay module and the servo. I looked into peak power for sg90 and thought I’d be ok with 800mA supply. I had a spare power module so decided to wire it in at the terminal block on the farm, powering just the servo (connected 0v to other 0v from control box). Tested it and servo worked fine at speed.
I’m guessing it’s one of two things. Either the supply module isn’t sufficient for servo and other bits together or the wire I’ve used to connect control box to farm isn’t up to the job and is limiting the current supplied.
Whatever it is, the new setup seems ok for now.