The machine repair when the box out but not open, open the check movement not abnormal, the installed test machine that is not out of the box, only a slight "Da Da" sound, suspected connection component bad, replace the fault still, think it is out of the box operation, doubt the frame position detection switch problem, open carefully measured without open circuit, fault phenomenon, then carefully measuring the switch resistance, between the two sets of connection after cleaning, measurement of infinity should belong to normal, the installed test machine, out of the box is normal.W76service manual download site