I have successfully modified the new version of the power supply to support brightness adjustment.
I don't speak german, but through babelfish, this thread has been helpful to me. I thought I'd return the favour by explaining how I did the mod on the new power supply / CCFL controller.
The Adj -line connects to two pins on the LX6501 via 10K/10K resistor dividers: BRT_A and BRT_D. On this particular design, adjusting BRT_A, which should adjust the linear current to the lamps, leads to the chip reaching some error condition which makes it shut down. However, BRT_D does work. It adjusts the brightness by pulse width modulation.
To complete the mod, you need to separate BRT_A (pin 9 of the LX6501) from the Adj-line and connect it to the 5V rail as it was before. The Adj -line should only reach the BRT_D pin.
There are three resistors on the yellow side of the PCB, titled R201 R202 and R206. They are all next to a jumper bridge called JP214. R202 is the one leading to BRT_A and should be unsoldered from the end that is closer to JP214 and the large heatsinks.
After unsoldering that end of the resistor, you should take a piece of wire and solder one end of that to the loose end of the R202 resistor and the other end to 5V. I used the same spot where I had previously removed the R153 bridge from.
Now the BRT_A is connected just as it would have been before the mod and only the BRT_D, connected through R201, is adjusted via the potentiometer and the backlight is fully adjustable. If it's not clear yet, yes, you do need to complete the previous mod as well. This is just in addition to that. And for the record, I currently use a 2.2Kohm pot plus a 470 ohm resistor on the 5V side for that. Far from optimal, but is one working configuration.
So far I have noticed that the PWM adjustment is audibly noisy. There's a srrzzsszszsrrszt sound coming from the monitor power supply whenever the brightness is turned down. This is normal with PWM, but could conceivably put a greater stress on some of the cheap components inside the power supply, possibly leading to early death of some capacitor some time in the future. The noise is not particularly bothersome, but could be annoying in a really quiet room when not listening to music or movies.
Also, I have noticed some small artifacts on the screen every now and then. It could be that I just reconnected something a bit loosely when putting the screen back together, or the PWM could be creating enough electronic noise on the supply voltage to sometimes mess something up with the TFT controller circuits.
YMMV and do everything at your own risk!
Enjoy!
- Arto
