Purpose of the zener diode on the LPE200 LCD?

[mitaux8030]

Hi all,
I'm reading Installation Manual MM101478V1 R1A where it details a replacement procedure for the LCD display on the LPE200 / LPE50 / Prism. There's a kit to do this, and as part of the kit, they detail a zener diode to be installed between pins 2 & 4 of the LCD display. What is that for - what was the fault or situation that gave rise to this recommendation of fitting the zener? Just wondering if it's worthwhile me fitting this to my LPEs if they don't already have it there?

[Rescue1]

Could it be used as a makeshift voltage regulator maybe? I wish I had a pinout and could tell ya but I would guess it has something to do with that..Either way I would put one in..Good observation by the way...:-)