I have code 99 on my uniwell nx 5400 how do I fix it?

Hi. Error 99 (or EE-99) usually indicates loss of program. Normally caused by battery going flat (if left unplugged for too long). You need to re-program it. Checkout tech has the programming manual for this model:

https://the-checkout-tech.com/manuals/cashregisters/Uniwell1.php

Try just programming one or two things on it first, then power it off overnight. If it goes back to error 99, your battery is no good.

Registerman
April 2018