"Binder Dundat" wrote in message
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On Apr 1, 6:55 am, "Arfa Daily" wrote:
"Matthew Kirkcaldie" wrote in
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...

In article ,
"Arfa Daily" wrote:

First check that the sled movement is absolutely free - that there is
no
no
grease on the slides that has gone 'sticky'.

Could also be a gear with a missing tooth - I had a Sony Discman which
had that problem, about 20 minutes into a disc it would get stuck at
one
spot and just keep repeating. The missing gear tooth was on the drive
which moved the optical pickup from the centre to the edge during play.

Quite so, I'd forgotton that one, but you will of course pick up that
problem when checking the sled for freedom of movement. Another fairly
common one that can cause the same problem, is a split in the nylon
pinion
on the shaft of the sled motor. If you push the sled manually down the
slides, you can feel it go bump-bump-bump as the gears rotate. Nothing
can
be done about that one, except to replace the pinion from a scrap deck.

Arfa


Thanks, but I probably did not explain the problem very well, the
laser assembly moves back and forth fine. The problem with the outer
tracks is the sound quality deteriorates as you go farther out on the
edge of the discs. It is not skipping, it seems the sound goes high
and low and is slightly distorted as well?


OK. Well basically, it is not possible for the system used to play a CD, to
produce distorted sound as a result of track position, unless the system is
dropping so many bits, that it has got beyond the capabilities of the error
correction circuitry. This can occur as a result of tracks being closer to
the end of a disc, for one of two reasons. The first is a defective spindle
motor. As the laser tracks towards the edge of the disc, the disc's
rotational speed slows to maintain a constant data rate from the pickup. If
the motor gets poor, this can result in its shaft speed becoming erratic.
The slower the motor is running, the more pronounced the problem is, until
data starts to become so mis-timed that bits start getting dropped. This can
result in a harsh 'crackly' sort of distortion that can get as bad as total
music drop-out, as the error correction throws up its arms in dispair, and
instead mutes.

I have also known a similar thing to occur with a weak laser. Now in theory,
there is no real reason that this should happen, as the reduced disc speed,
should result in the laser seeing data at exactly the same rate. I suspect
that it is in fact a combination of both a slightly worn, and thus slightly
unstable motor, with a weak laser. If the laser is replaced, the marginal
motor becomes 'masked' and the player works fine again. Motor is now the
first place I would be looking.

Arfa