D800 dim display ...swapped with good display but still dim

I have a Dell Latitude D800 that now has a dim display from start-up to desktop (readable but certainly not bright enough to use without getting a headache). I have done the following:

1. Tried to adjust the brightness with the fn + arrow up/down keys - no change (same dim level up or down)
2. Hooked it up to an external monitor - the external monitor displays perfectly
   
3. Downloaded the latest Quickset application from dell to see if it would help the fn + arrow up/down keys - no change (same dim level up or down)
4. Adjusted the brightness in the BIOS to max for battery and with power -  no change
   
5. Did a diagnostic test on boot up and got the error message LCD Inverter Detection Test - Fail Error Code: 1000-0322
6. Swapped the the entire LCD display with a known working one - no change - (doesn't that rule out the inverter and the backlight?)
7. Downloaded the latest video drivers - no change

Any additional ideas for troubleshooting would be greatly appreciated.

Thanks