Under normal circumstances, into the disc, the laser head should be auto focus searching and disc reflection light generated current signal by amplifying ic301 (KA9201) RF into (KA8309 digital servo control, when reached the best focal point when KA9201 28 feet have focused FOK signal, 41 feet sent to the KA8309, Fok receives the signal, 39 feet from a spindle rotation signal. After amplifying and driving the rotation of the spindle. First check the drive tube are normal, the power measurement focus search voltage 39 pin 0V, without driving voltage output; 41 foot FOK input voltage 2.6V, while the normal FOK voltage of 3.2V, indicating the abnormal FOK signal. Using oscilloscope to test KA9201 foot eye, eye is messy and amplitude only 0.4V, normal should be at 1V ~ 1.4V, generally not less than 1V. Adjust the laser head potentiometer, increase the laser intensity is invalid after its recovery. When the movement turned over. The accidental discovery of the disc to rotate and lateral movement. Careful observation, found that the laser head of the laser head is less prominent, and the side stand out more than the amount of the laser head lens protruding too small, failed to reach the normal position. Then detect the focus of the drive output tube, voltage fluctuations in the 0V~O.4V between the normal voltage fluctuations in the OV-1.2V, the driving voltage is too low. Remove the drive pipe, test the performance of the poor, the new tube after the test machine, all normal.