I got one IR53H420 electronic ballast IC, but still no idea why last time everything went up in smoke. This is the schematic from datasheet and it is pretty simple. I noticed that LC resonant circuit connecting which is connected to lamp filaments was not in the same frequency as the ballasts output. And jet that could not be cause of burnt IC because this it can operate in preheat mode in which the output frequency is lower or higher than lamps LC circuit and it is not supposed to blow up.

While I was figuring out the problem I also gave a paint job to old scanners case and also drilled holes in the lid for 7-segment display and buttons.