The driver chips on the flex cables take LVDS signals and the timings needs to be correct. You won't be able to drive these "willy-nilly" - It's pretty complicated stuff. Also shining light onto the die will not do anything useful. You need to scan both horizontal and vertical for something to happen.

Thanks Per for the input. What more do you know about these driver chips - what do their outputs look like? At some point, something has to drive an (O)LED with + and -. Do you know how the LEDs are arranged - some sort of crossbar maybe? Where is the ultimate "driver", is it in these IC's or are there also transistors in the matrix?

There are 6 chips so does each one drive 1/6th of the  display?

So I've been taking a closer look at some of this today. It seems that the bare silicon chips attached to the flexi circuits are some sort of decoder/driver, and probably fan out even further to the thousands of LEDs on the front of the panel. It looks like there's a bussed digital interface to these chips that traverses the driver PCB's. So to make anything happen, I'm still at the level of a digital interface to poke data at the driver chips, and not at the "LED Matrix" level.

There aren't necessarily three subpixels per pixel. Some use more blue and/or red than green, due to efficiency and color rendition reasons. Maybe you (or someone) could find the data sheet for the panel.

Yeah the datasheet would be useful. Probably the Vdd and Vss voltages (relative to GND) would be the most useful numbers to be getting along with.