I fixed this one (replaced inverter board) a year or two ago. Now the backlight is intermittent. On examination, D22, near the video connector on the motherboard, appears to be toast. It's, of course, an sm device with no visual clue of it's value.
The four terminals on the inverter are: Pin 1: Ground Pin 2: +3.3 volts Pin 3: The variable leg (1.8 volts backlight off, 2.8 volts on) Pin 4: +19 volts
Metering reveals that one end of D22 is connected to ground, the other to Pin 3 on the inverter (through the video flex cable). Touching D22 turns the backlight on, even though one end appears to be nearly burnt away. Shorting Pin 2 to Pin 3 has the same effect, although it cannot be dimmed in this state.
Would I be correct in assuming (actually 'suspecting') D22 is a zener diode, somehow involved in dimming the backlight? Would the 2.8 volts measured at Pin 3 be a clue as to it's value; or am I totally off base?
Any other ideas as to a suitable replacement; or should I just stick something like a 1n4148 across there as an experiment? It's hard to power the unit up disassembled, but it could be done.....
jak jak