Samsung ER-4940 won't stop running & no display?

If an IC has failed that badly, you will normally find a power supply has also failed or there are other shorted/ open/ leaky components associated with the IC. It sounds like it is probably a motor driver IC that you have replaced. I would check that you have the correct power supplies to the IC first.
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If anyone needs to program a Samsung ER-4940 cash register, the manual is here:

http://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-4940_dealer_pocket_programming_guide_manual.html

Registerman
May 2011