This is probably a red herring but mine failed doing an SWR sweep after cutting a new 40m EFHW. I was feeling lazy and instead of getting the NanoVNA out and calibrating it to tune it up, I just used the QMX. The antenna was grounded but didn't have a common mode choke and I heard the chatter in my computer speakers when it was sweeping. Wouldn't receive after that despite a 1.1:1 SWR. But after an adventure in surface mount de-soldering to replace IC402, adding the diode, and putting on a proper choke everything is working great. I had done a number of sweeps in the weeks prior to this, but it was always after having the antenna already dialed in with the VNA. Could just be coincidence, but I've not read anything about what people were doing when theirs failed, so just throwing this out there to see if it helps.
