I assumed the monitor uses CCFL lighting due to its thickness, but perhaps it is just as well to be sure. I found a user manual, but the type of lighting does not seem to be stated there, which in itself suggests it is not LED. I found a service manual for the S2309Wc but not the S2309Wb and this seems to confirm that it is indeed using CCFL, but from the below I have reason to believe that there has been considerable revision between the 'b' and the 'c' version, as the board layouts do not match what I have. It would seem unlikely that the lighting technology will have changed from LED back to CCFL though.
I did identify the on/off signal from the logic board to the main board, and can confirm that this goes high when the On switch is pressed, and it stays high. I am also seeing the DIM line (labelled BRT_AD on the circuit board) go high with two alternating going low square pulses, one long, on short, at regular intervals. They come on at power on for several seconds, stop for a couple of seconds, then resume again continuously.
Page 57 has a diagram to follow in the event that there is no back light, but here it gets confusing. I checked the power at R802 - it was almost exactly 5.00v. The diagram states that it should be 13v. After the resistor and at the chip pin it is almost exactly 3.33v. IC801 pin 13 is also supposed to be 13v. I get 0v. So I looked back at the circuit. R802 should be between the power rail and Q801, not at IC801. Pin 12 of Q801 is VCC, but on this board it leads back to a capacitor. I decided to follow the circuit back from the On/Off signal pin. Instead of passing via a 10k resistor to Q801, which turns on Q802, which in turn supplies power to the IC turning it on, the line leads to a 4.7k resistor which then goes directly to pin 10 of IC801. So it seems the layout is different and perhaps a different IC part has been used in this version. Perhaps this explains why Q801 and Q802 cannot be found. So clearly the board layout did not match the circuit diagram. Evidently I need a circuit for the 'b' version, but so far, I have not found it.
While I was at it, I did check the temperature of various semiconductors - including IC801 - with a temperature probe. Nothing seems to be running more than a degree or two above the ambient room temperature, except perhaps regulators, which run a little, but not much hotter than this.
Since the 'On' signal seems to be present and the 4.7k resistor is OK, this would seem to point to IC801 as the source of the problem, although I firt need to figure out whether there is actually a 13v line on this board, because I am not seeing 13v anywhere. There should be 13v on one of the pins of the connector that runs between the two boards. I only see 5v and 3.3v lines and again, the pins are not in the order that they are shown in the service manual.