my er-150 making buzzing sounds?

If it is a continuous buzz, then you may have changed modes without finishing. turn the key to see if it stops buzzing in a certain mode (apart from off mode). If it does, finish what you were doing in that mode, then turn the key.

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If anyone is looking for Samsung ER-150 or ER-150II manuals, C-tech collective have them here:
http://the-checkout-tech.com/manuals/cashregisters/samsung1.php

Registerman
October 2010