Sony S530D manual Focus, Search, Servo

Focus

Mechanical focus of the laser beam on the information layer of the disc is accomplished by moving the laser’s objective (final) lens closer to or away from the disc. Applying a current to a coil that is attached to the lens controls the lens position. When the lens moves up and down, so does its corresponding focus point at the disc area. Focus is found when the laser’s focus point rests on the information layer of the disc.

Search

There is a large and a small lens movement associated with focus. The large up and down lens movement is used to locate a disc by moving the focus point until it finds the disc layer. This large lens movement is called focus search and can be seen by observing the lens after the tray moves in.

Focus search employs five ICs and the focus coil. System Control IC202 initiates focus search by sending data to IC701 which makes voltage to move the lens. The results of the search are sent as data from IC701 back to IC202 on the parallel bus so a stop search command from IC202 can follow. Details of the IC202 and IC701 bi-directional communications are explained later.

Focus Search Devices

Device		Purpose
System Control IC202	Retrieves and acts on the focus search
	program stored in memory
EEProm Memory IC201	Stores focus search sequence
HGA IC601	Expansion port for IC202
Servo IC701	∙	Translates digital commands to
		analog focus coil voltages
	∙	Identifies disc’s layer using IC001
Driver IC801	Voltage to current coil driver
Focus coil	Moves objective lens
RF Amp IC001	Feedback to electrically identify focus

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Focus Search End – Disc Identification

Focus search concludes when focus is found or when the search cycle is over and no disc was found. Using A to D laser diode signals from the optical base unit electrically identifies the mechanical focus on the disc layer. RF Amp IC001 combines them to output PI (pin 29) and FE (pin

40)signals. Both are needed to find the focus position and stop focus search. PI identifies a disc when the signal goes high. FE identifies the focus position as this line rises and crosses 1.8V on the way down during search.

Once the focus position has been found, the lens search operation ends and the servo operation begins. IC701 makes the crossover by informing System Control IC202 the disc layer has been found when FCSON from IC701/pin 39 goes high. It remains high as long as focus is maintained by servo IC701.

Servo

Once the disc layer is found during focus search, smaller lens move- ments maintain focus as the disc is spun during playback. The focus servo uses three ICs to provide small correction voltages to the focus coil:

	Focus Servo Devices
Device	Purpose
RF Amp IC001	Feedback to electrically identify focus
Servo IC701	Identifies disc’s layer position using IC001
Driver IC801	Voltage to current coil driver
Focus coil	Corrects objective lens position

The FE signal from IC001/pin 40 is used not only to stop focus search, but also to maintain playback focus. This error signal is amplified and output IC701/pins 7 and 9 to drive the focus coil.