x61 Backlight Issue

[KevinNZ]

My favour that has become a nightmare! Customers daughter has (had) an X61. She managed to stand on the laptop (something on the top shelf I suppose). Anyway it was immediately evident that the LCD panel was broken and I offered to replace it for her.
1. LCD panel was purchased and installed and working fine, unfortunatley a few of the indicator lights on the inverter were not.

2. I ordered a new LCD cable and inverter to be sure that the second procedure would cure the lights and any other issues. At this point the backlight suddenly stopped working. I guessed that this was probably the inverter since I already had issues with some indicator lights.

3.The new parts arrive and are installed, indicator lights are now all OK but the backlight is still dead.
- No power coming from the inverter so unlikely that there is a problem with the (new) LCD panel
- Reset BIOS incase it had become confused during the surgery
- Lid close switch is working correctly
- plugs/connections all checked

4. Logic leads me to conclude that the problem must lie on the mainboard. The cost of a mainboard is going to push the parts cost to more than the cost of a new laptop.

Any light (pun not intentional) on the subject would be most welcome

Or more specifically has anyone perhaps had board level experience with the backlight circuitry on the mainboard?

[Harryc]

Make sure that the polarity is correct on the plug from the backlight into the inverter, and that it is pushed ALL the way in,

[KevinNZ]

Thanks for the reply. All plugs have been thoroughly checked. I have no voltage emanating from the inverter so I am certain my problem lies before the inverter (since it is a new part). I in fact tested the original inverter and all its indicator lights work now so the original problem seems to have been the LCD cable.
There is something that is bothering me. The mounting bracket for the inverter is screwed up against an earth on the LCD cable, this earth is continuous, via the bracket onto the inverter board. During my fault finding escapade of swapping between the old and new inverters, I did not have this bracket mounted (it is not supplied with the new part). It worries me a bit now that this earth may be required to supply the full current required by the inverter, and whilst not connected this current may have been flowing via an underated path causing the damage. On the other hand I suppose you would expect that even if that were the case, remounting the bracket would bypass any such damage.

[KevinNZ]

The problem was solved by replacing fuse F2 on the motherboard. It is located just to the left of the LCD cable connector. The fuse is a Littlefuse (very fast blow) 476 series, 3A. I have images if you need further visuals.