Open the cover to check, add VCD discs, disc rotation that found in disc, third disc retrieval until finished, screen to display DISC. Because the machine is Philips three disc machine, servo circuit board in the table below, not conducive to over maintenance, only the servo plate removed alone, connected with the data line and the motherboard, flat head after overhaul. Energized after the hand is closed at the same time SW1, SW2, SW3 switch, observe the laser head laser light is normal, focusing, tracking movement, put the plate after the multimeter is used to measure the formation of FOK integrated block OM52842 feet, low level does not jump. Due to the change of the level moment normal disc rotation, FOK no level change, the high frequency signal is composed of QS01, QS02, QS03 amplifier, limiting amplifier, envelope detection and switch tube and other components of the discrete FOK detection circuit failure or laser aging, used the new laser head replacement pilot, fault phenomenon invariant, eliminates bald reason, to focus on examination of the FOK circuit. The servo plate resistance capacitance parts for small SMD components, has the certain difficulty in the road test, but as long as carefully, or easy to detect the fault point.4qEservice manual download site