These are a great old scale. I still love working on them. The problem is usually caused by drift. This means that the scale can't get a stable reading so it won't zero. The reason for this is that the power supply probably needs new capacitors. You can often see a slight flicker on the display when the capacitors are old. It is not too difficult to repair (if it is the caps) and it is usually worth having it done as they give very little trouble (keypad wears but this is usually repairable too)
Registerman, April 2013
