Sam Goldwasser said:
See the CD Player Repair guide at the site below.
The sled should not be shaking back and forth, only the lens. The sled
should just move occasionally to maintain the lens centered withint its
range.
I agree with Sam. As to whether the player needs to see a disc on the
turntable to spin it up, this depends on the unit. Some players will just go
ahead and turn on the laser, and spin up the disc, as soon as a 'laser home'
signal is detected. Some coarse speed adjustments then take place, along
with focus seek, until the spindle servo starts to see valid data coming off
the disc, whereupon, it will lock, and the rotational speed will stabilize
to the correct value. Other players will switch on the laser as soon as the
home signal is detected, and go ahead and look for a reflection from a disc.
Coarse focus search will take place at the same time, until the focus servo
locks. At this point, the drive to the spindle motor will be switched on,
and the data search will commence. Some players, if they fail to detect an
initial reflection, will pulse the spindle motor to rotate the disc some, in
case there was a jammy fingermark right above the lens, so there is no
simple answer to your question regarding the point at which the disc should
start to spin.
Whether or not the deck is on the tilt, the outgoing and returning beams,
should not hit any different place on the disc, or the pickup photodiode
array. This is the whole purpose of the tracking and focus servos. The lens
suspension is very soft, and the mass of the suspension and lens is very
small. The focus and tracking motors, which are actually like tiny
loudspeakers acting on the lens suspension in all directions, are plenty
pwerful enough to hold the lens in the right place, irrespective of gravity
acting on the pickup in any direction.
When the disc is rotating, you should be able to see the lens moving up and
down a little, as it follows the irregularities in the flatness of the disc
( don't believe the specs about disc flatness and eccentricity ... ) You may
also be able to see *slight* side to side movement of the lens if the disc
is particularly eccentric. To see these movements, you will need to be on
the last track of the disc so that the lens is at the disc edge. These are
the only movements that you should see with the disc playing normally. The
laser is moved on by another motor via a gear reduction system.
Approximately once every four to six seconds, you should see the whole laser
head move on by about one tooth. This movement should be smooth and regular,
and there should not be any overshoot. You certainly should not see any
shaking or violent movements of the lens, or pickup, in normal play. If the
problem is within the laser, then I think that it would have to be something
like a loose critical-angle mirror, that only lays in the right place with
the laser tipped, in which case, the only solution would be a replacement
laser. What laser type is fitted, as a matter of interest ? Many Sony lasers
are really quite cheap. Also, I take it that the disc is clamping correctly
to the turntable ?
Regarding your question about the three lasers. It does not have three
lasers as such. It is a single laser diode, whose output passes through a
splitter, to create three beams. The middle one of these is the one which
should be centred on the disc's spiral data track. This is accomplished by
keeping the two side beams an even distance either side of the track. To do
this, these two beams are focused onto two diodes in the pickup array. They
are called the "E" diode and "F" diode - hence the servo adjustment "E-F
balance". When the middle beam is exactly on the disc track, and the E-F
balance adjustment is set correctly, the outputs from the E and F diodes
will be equal, and there will be a null servo condition. As soon as the beam
moves off track, the E-F output will become unbalanced, and a positive or
negative servo condition will be created to correct the beam path. Focus
servo operation is likewise based on signal imbalance, but this time as a
result of the central beam being focused onto the "A", "B", "C" and "D"
diodes. When the beam is correctly in focus, it will be circular, and all
four diodes will be equally illuminated. If the beam is out of focus, an
astigmatic condition will be created, illuminating two of the diodes by a
greater degree, creating an inbalance, which drives the focus servo in the
appropriate direction to restore correct focus. Which two diodes are
illuminated more, depends on which direction the beam is out of focus. Data
output is the result of adding the outputs from these four diodes.
Not all optical blocks are 3 beam. Some are single, and use a completely
different scheme for deriving the servo information.
Arfa
