"Mark D. Zacharias" wrote in message
. com...
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.
A couple of years back, I had in a boombox type player for repair - Pan as I
recall - and it had had a " Disco " mod put in it. This comprised a VCO IC
and a remote pot. It was a professionally made item, and had a proper
silk-screened self-adhesive panel foil to go around the pot on the outside
of the case. This foil carried the legend " Pitch ". The system clock
crystal had been removed, and the output from this VCO substituted by wire,
directly into one of the vacated print holes. Rotation of the pot provided a
very effective and smooth pitch variation, which easily matched the +/- 16%
that you see on the semi-pro bedroom studio units.
As far as I can see, variation of the servo clock frequency, is the only way
that the OP's problem can be occuring. I agree with everyone else, that as
soon as the data rate falls below the minimum buffer memory 'evening out'
capability, the result will be data dropout initially, followed by full
muting, as the servos drop out of lock.
Arfa