tim309 said:
Thanks Arfa, good advice and mission accomplished, at least for the
lense cleaning. Once I'd taken the cover off I realised that the real
problem was that the drive motor sometimes doesn't spin up. I tried the
finger encouragement but with no success. Initial suspicion would be a
faulty micro switch or similar which presumably enables the motor to
spin up the CD once the tray is closed. I don't know specifically how
the mechanisim is set up without doing a major strip down which I'm
reluctant to do until I've been able to explore all possible options.
Do you have any more advise for me? Incidently, i notice the CD drive
assembly is of philips origin.
Could be many things. What is the drive ? A CDM 12.1 or a 2201 maybe ?
Usually, the sequence of events is :- tray closes, and "tray in" switch is
made. This tells the system control micro that it can go ahead and start the
TOC read sequence. Next, the sled motor will normally be driven back and
forth a small amount to check that the laser is "home". There is a leaf
switch that is pressed by the laser assembly to tell the micro that it is
home. The system control micro then turns on the laser. At this point, what
happens next depends on the player. Usually, the player will start the focus
search operation, which is normally a maximum of three full up-down
excursions of the lens, before it gives up, which may be because there is no
disc in there, or the pickup is faulty, or the laser is not burning, or weak
output. If all is well, the laser should obtain focus within one up-down
cycle, and the focus servo will lock and produce a focus true signal. This
should result in the spindle and tracking servos being turned on, and the
disc should spin up, whilst the tracking servo attempts to lock on the data
that should now be streaming off the disc. Once the tracking servo has
locked and good data is coming off the disc, the spindle servo will be fine
tuned to correct the rotational speed of the disc, and proper data reading
will then take place and the disc's TOC will be read. When this has happened
successfully, the spindle motor will be electronically braked, and the
laser, focus and tracking servos will all be turned off.
Some players deviate from this sequence once the laser has been turned on,
and just go ahead and spin up the disc to some coarsely maintained speed,
whilst focus seek and tracking seek are taking place. Once they have
happened successfully, and their servos are locked, the spindle servo will
be locked. This sequence of events results in a quicker TOC read from a
standing start.
Some other players don't give up immediately after 3 focus tries. Instead,
they rotate the disc just a bit, and try again, in case there was a jammy
fingerprint on the disc right above the lens. This may repeat several times,
before the player gives up.
The key to figuring what's going wrong on your player, will likely be
observation. Try watching carefully how the deck responds when there is no
disc inserted. If it seems totally inert, try opening and closing the tray a
number of times to see if it ever does spring to life, which might indicate
a problem with the tray closed sense switch ( the tray motor might also be
trying to still run, even after the tray is fully in ).
If it always does something, then try again with a disc in. Try to get it
into a position where you can see what the laser is doing under the disc. If
it does run up ok, watch and note the sequence of events, then try opening
and closing again, until it doesn't work, and see what changed. Also, vice
versa. If you see the laser shuffle take place when it does work ok, but
not, or in a different way, when it doesn't work, this might indicate an
iffy laser home switch. If nothing appears to fundamentally change up to the
point where the disc should spin up, between working or not, then you could
have an intermittently faulty, or very marginal laser. The Philips ones
certainly do fail, and mostly come as a complete deck assembly, and are not
hugely expensive. All of this assumes that it is not one of the early
Philips radial arm decks, of course ...
Arfa
