The machine uses Samsung PCB-802 motherboard, SONY KSS-212B laser head. First, clean the lens head and try to fine head laser trimming resistance, still can not read dish. With a new head replacement under the original head, the result is still a failure, the normal head. RF signal processing circuit KA9201 each pin static voltage, no abnormal. Analysis that should focus on the DSP circuit. Measurement of KS9211B external crystal 16.9344MHz two voltage, respectively 2.2V and 2.08V, normal. When the measured data output end and found both in reading the disc or to stop reading disc were no output voltage (normally due to the voltage of 2.5V), lrck and BCK feet were 2.5V output voltage is normal. In order to determine whether the KS9211B fault or decompression board fault, disconnect the DATA to extract the board connection, the test voltage is still 0V, determine the fault in the KS921lB circuit. Check, no abnormality was found in the peripheral circuit, after the removal of the substitution of a genuine KS9211B into disc through electrical test machine, immediately read total tracks, and troubleshooting.