Hi Stan and Ludwig, thanks for the help! I think now I know what happened.
?
b) as I think Ludwig suggests, the BS170s had suffered some damage, and finally broke, sending a 12V over-voltage into IC503 outputs, frying it.
I believe this was indeed what happened:
?
1. I did attempt SSB calibration from the on-device menu a few times although I stopped them promptly. Even though, BS170s were somewhat damaged due to the fact that I didn't install LPF for 160M. The SSB calibration initiated from the on-device menu always starts from the lowest band and it doesn't honor the TX disable setting (I validated it on my QMX HB).
?
2. The 40W Anker charger is innocent. It failed to fully power on QMX+ probably because at that time IC503 had been damaged already which in turn caused a short in the 12V rail via BS170s. The 40W charger was just protecting itself from over-current.
?
3. Switching to other power sources made things worse because it allowed ever higher current to pass through... I guess the reason why running the diagnosis terminal app would crash the controller is because it would disable the PA voltage which would cause an abrupt stop of the high current in the 12V rail which would in turn cause a high induced voltage (probably due to L502?) to trigger the protection in 3.3V SMPS somehow?
?
This morning I tested my QMX HB with that 40W Anker and it was completely normal. After that, guess what, I made another stupid mistake...
But in receive, the TX signal into IC503 is off, so the BS170s never get turned on, never conduct current. ?At least if IC503 isn't broken
Then I tried to power on my QMX+ with that 40W Anker to see if it would work. It did power on fully, but this time I connected the USB-C meter in-line and I immediately noticed the input power was 14W in RX. What happened? ?Well I replaced all the BS170s yesterday, but IC503 was not there so the gates were floating. After the initialization, the firmware would turn on the PA voltage even for RX which fried half of the BS170s in seconds...
?
Sigh, I've learned so many lessons from my mistakes this weekend... One suggestion to Hans, maybe a self recovery 2A fuse could be added to the 12V rail?
?
Thanks again to Stan and Ludwig!
?
73 N6HAN
?
