FSLCD and Backlighting

Hi ppl,I am having a weird time understand some of the complex wiring involved with some models of Text LCD displays.I have used FSLCD and got one 20x2 running fine (with backlight) for fuel, etc in my overhead.I have another 20x2, of which I am using one row to display IRU info also working fine.I have two other units that I cannot get the backlight working. They look the same, but no matter what I do they won't light up. I have a nice 20x4 for the MIP and 16x2 I am using for pressure on my o/head (in place of a guage). The schematics are all the same (i.e. A = 5v+ Anode, and K a 0V Cathode - Pins 15 and 16.I have tried using different pots (both 100K and 10K) in the hope it was something there, but nada.Any ideas or help would be appreciated.CheersChris