First I have a 4x20 VFD in an enclosure and probably everyone knows that twang kind of sound you hear if you set a VFD down with a small knock. If I lift the enclosure just on one edge perhaps 5mm to 10mm and let it drop on my desk, I'll hear it and also you can see some of the display vibrate if it is on.
I decided to test a display that is not in the enclosure to see if it would exhibit the same behavior, so I connected it to a pcb, and gave it a few small knocks. I know these are made of glass so the knocks were very very light, more like taps really. The one outside the enclosure began to die! It started fading in the center, kept fading, and eventually was completely faded. I was surprised as I would have thought these things would be more durable.
I called the manufacturer and they were super and are sending me a replacement, but he told me that he doesn't think it is a loss of vacuum based on the color of the dot in the corner of the display. He said it would turn white if the vacuum is lost. If it isn't a loss of vacuum, could the shock have caused an overcurrent situation on the main pcb that is part of the problem? He mentioned the fuse, but the fuse is still closed and it still draws 300mA when the factory test screen is supposed to be on.
Any thoughts on what I might look at first for fun to see what I can figure out? Perhaps the circuit that generates the higher voltage to drive the glass?