If you have access to an oscilloscope, the HF "eye" pattern can be
observed,
and may be noisy. This would account for the deteriorated performance
first
on CD-R's. As previously noted, this is often the result of dust and
smoke
contamination. The finest particles get inside the laser, and settle on
the
turning mirror as a fine film. This diffuses the reflected laser light
coming back off the disc before it can really be read. It is sometimes
worthwhile to adjust the Focus Offset for maximum amplitude as viewed on
the
scope. If it makes a difference of about 20% or more, this may solve
your
problem, at least for the short term.


Mark Z.

Mark Z.


Hello

I have an old Telequipment scope who goes up to 1 mhz, it should do the
job.

I've look on the main pcb and there is 4 trimpot; T.BAL , F.BAL , FEOF ,
TEOF

Wich one are for adjusting the Focus Offset ?

Thank a lot

Gaetan


FEOF should be the one, but a 1 meg scope won't really get it. You can
adjust for maximum envelope size, which probably is good enough, but you
can't look at the diamond shaped center area of the expanded "eye" pattern
as viewed on a 30mHz or higher scope. Sometimes a x10 probe is required,
but in my experience it is rare for a direct probe to load down this
measurement.

You can "Google CD eye pattern" and see what I'm talking about.

Mark Z.

All that Mark says, but before you start, CAREFULLY mark the EXACT positions
of the pots before attempting adjustment. If you do adjust more than one of
them (the temptation *will* be there - trust me !!) and you do not have the
proper bandwidth 'scope, and the experience to know exactly what you are
adjusting and why, it is staggeringly easy to get those pots to a point
where nothing will be read at all, often with just a few degrees
mispositioning of a couple of them. Re-finding the correct places to get it
going again, can then be a most frustrating excercise ...

Arfa