I don't have a manual with me, but I can tell you that the KN53 does not use an LCD display. It is a gas-discharge display that only Bendix/King dealers can get from the manufacturer. Replacing them is not that complicated, although there are some very fragile contacts that support that display.
What is your display doing exactly? If the display is not completely dead, you could try to remove it from its mounting contacts, and clean the contacts with an pencil eraser. Also, the display is made by sandwiching 2 glass plates together. Over time, metal migrates between the contacts under the glass, sometimes cleaning the metal migrations would fix problems like erroneous segments partially turning on. This happens because the display operates at about 190VDC. If you do clean the display, or if you install a new one for that matter, make sure you spread some DOW 4 over the contacts to avoid the metal migration.
Good luck. Let me know if you have any questions, and I'll try to answer them the best I can. Disclaimer: Even though I have done this in an avionics shop, I can take no responsibility for someone else trying it at home! There, hopefully that will satisfy my lawyer.
A&P, IA, Avionics Tech, and finally: Pilot! (12/28/06)
Dying to build an RV10. Not quite ready yet