Sled Motor Drive - PB
67
Sled Movement to Another Location
Initially during disc search, just System Control IC202 data was used to move the sled motor. During playback, IC202 data and tracking error are used to handle the sled movement. The choice is dependent upon the location of disc information. When the disc is played linearly requiring smooth sled travel, the tracking error signal is used to follow the track. When information must be retrieved at a different part of the disc, System Control IC202 instructs the sled to momentary move the laser assembly to another location.
Following the Track
When playing a CD, and most of the time when playing a DVD, the sled is periodically pulsed or “kicked” ahead so the tracking coil can remain within operating range of the new disc information. These sled kick pulses origi- nate from the linear tracking error signal taken from Tracking Coil Driver IC801/pin 6. This error signal is amplified internally and output IC801/pin 7.
The amplified tracking error signal is LPF by R707 and C705 before en- tering IC702/pin 3. With C706 positioned between IC702/pins 1 and 2 for negative feedback, IC702 is configured as an active LPF. These two low pass filters remove the instantaneous tracking error “noise” component. What is left is a DC voltage that increases when the tracking servo ap- proaches its mechanical limit.
The DC component of the tracking error signal is passed onto Servo IC701/ pin 66. IC701 makes a judgment about the input voltage level. When a DC threshold is reached, IC701 “kicks” or rotates the sled motor forward (laser outward) one step. The movement of the sled motor returns the laser assembly to the center range of the tracking servo. This causes the tracking error’s DC voltage component to drop below the sled movement threshold.
Supplemental information can be found in different locations on the DVD disc. When this information is called for, the sled is asked to move to approximately that location. The disc information is played to determine how close the laser is to the target. IC202 then decides to make a smaller jump or remain where it is.
This sled movement is controlled by System Control IC202 after receiving disc information from ARP2 IC303. IC202 communicates with IC701 on the parallel bus in order to have IC701 move the sled. Once the sled is moved, System Control IC202 waits for disc information (from Processor IC303) to determine if the laser is close enough to the target information before requesting another sled movement. If no sled movement is called for, the laser plays through the supplemental information. Afterwards IC202 instructs the laser to return to where it originated to resume normal playback.
IC Summary Chart
ICs involved in Sled Movement
Disc Identification | DVD Playback | CD Playback |
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IC202 | IC001 (TK51 Bd) | IC001 (TK51 Bd) |
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IC601 | IC303 | IC701 |
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IC701 | IC202 | IC702 |
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IC802 | IC601 | IC801 |
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| IC701 | IC802 |
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| IC702 |
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| IC801 |
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| IC802 |
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