Dell Mini 10v backlight PWM investigation

My Dell Mini 10v netbook has an LED backlight, with PWM brightness control at about 200Hz. I find the flicker very annoying, and I'm not the only person who's annoyed by PWM flicker. I've previously done some tests with an LED and a 555 timer and I can see LED flicker up to about 10kHz when I move my eyes quickly. The backlight flicker isn't visible with the brightness set to maximum, but that wastes power so I disassembled the Mini 10v to see if it's possible to modify it to fix the problem.

The Mini 10v is not easy to disassemble. The service manual available from Dell's webpage gives only brief instructions. Most parts are held together with plastic clips which require a lot of force to open.

The keyboard module removed:

Keyboard module removed

The palm rest removed:

Palm rest removed

The palm rest bracket removed:

Palm rest bracket removed

This was especially difficult, and I accidentally broke the plastic holding one of the threaded inserts. Parts of the plastic went flying and I couldn't find them, so repair will be difficult, but I suspect it will hold together well enough even with one of the screws missing.

Accidental damage to palm rest bracket

There are two sets of wires going to the screen. The wires on the left are the wireless antenna, so everything else goes through the 40 pin LVDS connector:

LVDS cable to screen

There doesn't appear to be any standard for these connectors, so I powered the machine on and probed individual pins. The screen defaults to medium brightness even with no hard disk installed, so I searched for a PWM signal.

Powered up for testing

I found a 3.3V PWM signal on pin 7:

200Hz PWM signal on pin 7

I disassembled the screen to check if it would be easier to tap into the signal at that end, but the connector is very small and there's no obvious point on the board to modify. The wire is wrapped in a shielding mesh tube and looks somewhat fragile so I don't want to modify the wire either.

LVDS connector in screen module

This leaves the LVDS connector on the main board as the best point for modification. I'll need to break the connection to the pad on pin 7 somehow and route it to an MCU and then feed a new higher frequency PWM signal back to the pin. There's an 11V supply on another pin I can use for power. I'm not sure the best way to go about this. It might be easiest to desolder the whole connector and drill through it to break the connection.

LVDS connector on main board

I'll think about this and continue later if I think of a good solution.

blogroll