dear adafruit and others, it looks like i have the same problem that mentioned in this thread.
first test OK, second OK (55.6V) , third failed, the tube does not light up. I checked the voltage on the Q3 transistor (without the tube): collector, emitter 4.7V seems OK. base 0V, wrong(?). I resoldered the Q3 transistors legs, and double checked the soldering. I checked the voltage on the microcontrollers pin that connects to the base, and it is also 0V.
Thanks for helping in advance.
PS: The PCB was maybe hurt where the red circle is, during the cut of the soldered end.