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Annax flipdot display reverse engineering

I bought a flipdot display a few years ago and finally decided to open it up and figure out how it works!

I'm certainly not the first person to play around with these modules. Someone else got their hands on the same Annax flipdot panels ZM16C30) that my display has, figured out how the panels are wired, and built their own control board for them. Here, I'll focus more on the original control board.

There are several parts, which I will publish and extend over time (for now, the first two parts are available):

The front side of the display unit. A flip-dot matrix display shows the text "Würzburg" in green text on black background, with some stuck pixels. All in a black metal box with two silver carrying handles. The front of the control PCB. On the edges there are four 40-pin connectors for ribbon cables and an army of driver ICs arranged around them. On the top edge there are a bunch of industrial-looking power and/or bus data connectors. Otherwise, the board is dominated by a 100-pin Siemens C509 MCU in the center, a power area with a large heatsink, and a bunch of other components described later in the text. The back of the control PCB, looking slightly less messy than the front, with a few shift register ICs all over the place. A combined view of the front and back side overlayed, aligned, with the front appearing red and the back appearing blue. Visually, it is unclear if this makes it easier or harder to trace the connections between the components. The inside cabling of the display unit, with the control PCB, the back side of the flipdot panels, and cabling. There are several 40-pin ribbon cables stacked on top of each other going from the control PCB to the panels. Some cables are connected to multiple panels. On top, there is a bundle of green wires running to the modules, and a few other cables that lead to the outside connector. Focus on the back of a flipdot panel. There is a large number of solder joints for the dot matrix. One can also see that each panel has two 40-pin ribbon connectors and a single green wire running to them. On the panel PCB, there are only very few electronic components.