n cook wrote:
Mark D. Zacharias wrote in message
.net...
wrote:
Couldn't that only happen if the clock frequency slowed due to a
faulty crystal or loose loading cap or related fault.

I suppose it could be that or even a mechanical failure (servo motor
problem,
not enough lubrication, spindle off center, spindle bent), power
supply rails at the motor or controller not to spec (too low or too
high). I'm just wondering what the most likely causes are for the
scenario that I've presented.

Mike


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

A regular CD player can only slow down a small bit and still get
intelligible audio. As it slows down a bit, the sound may get
static-y and at some point probably cut out. Decoder IC's are locked
to the incoming signal via a crystal oscillator. If the frame
drop-out exceeds a certain amount, they just mute or stop playing.
Don't adjust the potentiometer on the pickup - this is a laser power
adjustment and at best it would accomplish nothing for you, at worst
it would destroy the laser diode.
Wouldn't hurt to clean the lens and lube the spindle motor top
bearing - but don't expect any miracles.

Mark Z.



I would have thought a bit of braking would have no effect until its
run out of repeat redundant code and then drop out rather than drop
pitch.
Next time I have one open I will try loading the timing crystal and
see if that drops the pitch even if only for 1/2 second or so.
I've come across a cracked crystal from being dropped causing
intermittent problems, not in a CD though.


I've tried the old "drag down the rotation a bit by placing your finger
along the edge of the spinning disc" on a number of players over the years.
You have to be pretty careful about how much drag you impart to the disc,
but the effects are pretty readily observable. It's rare that you'd really
get any useful info from this technique, I'll admit. Mostly just testing for
borderline playing problems, like decoder IC's which seem to be putting out
a bad duty cycle for the spindle drive. You can observe the spindle motor
drive waveform during startup (100%), during disc run (around 50%), and vary
it a bit by the method I described. You can get a pretty good idea if your
problem is mechanical or a circuit problem. Of course, these days players
are so cheap, and test points so difficult to find or get to, that this type
of troubleshooting isn't done much anymore.


Mark Z.