@Takata
Wonder on basis of chklsts you provided whether, whatever the cause (small explosion not excluded), fltcrew as per prescribed drills did shed the AC BUS1 by shutting down GEN1, while the GEN2 driven electrical system was compromised, and may have hampered transfer to AC ESS FEED. May well explain the transponder going down too around 02:30, like everything electrical on board, including ability to communicate or to get transponder setting 7700 effectively through.
In addition, this is of course still to be confirmed, if I understood it well from the Greek defence ministers' report, the manoeuvres of MS804 (90° left, followed by 360° right, rapidly descending) took place between 02:27 and 02:29. Never mind the FR24 report that A/C maintained heading and altitude until 02:30, which is likely to be based on extrapolation.
Regards