[isw]

In article ,
"Mark Zacharias" wrote:

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"Soundhaspriority" wrote in message
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"isw" wrote in message
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In article ,
"Soundhaspriority" wrote:

I've got a 202ES player where the motor does not reliably start. If it
starts, it runs at the correct speed. Usage was very light.

Is there any active circuitry inside the motor, or just a Hall effect
sensor?

How many poles does it have?

Just about every CD spindle motor I've ever seen has been a "universal"
type with brushes.

My guess is that there's some dirt or corrosion in or around the
commutator. Take it apart (carefully, or you'll ruin the brushes), and
give things a good polish. Be sure to look for faulty solder joints on
the armature, too.

Isaac

Hi, Isaac. Thanks for your response. I'm shocked it has a commutator.
How is constant speed maintained?

Bob Morein
(310) 237-6511




Timing data is recovered from the cd itself and frame sync is maintained
by the decoder IC and motor drive circuit.

And inertia. Plus, motor speed isn't critical if the data is being
buffered.


Well, inertia figures into the equation, I am sure, but if you look at the
drive waveform from the decoder IC to the motor drive IC, you will see some
interesting stuff. The envelope shows a center line with components above
and below zero. Spread it out a bit and you will see the positive and
negative spikes. The negative spikes are braking pulses used to help
maintain servo lock.

When a CD is first spinning up, all the spikes are positive, a 100 % duty
cycle. As servo lock is achieved, it drops to near 50 %. When the STOP
button is press, the spikes are all negative for 2 or 3 seconds so the disc
stops quicker.

Earlier motor drive IC's were essentially power op-amps driving one motor
lead positive or negative with respect to ground. Any more they are BTL
drive, with both motor leads actively driven by the chip.

Data buffering is used on newer models, including DVD players and MP3
compatible models. I don't think earlier CD models used it. So long as frame
sync is maintained within spec, the Reed-Solomon code takes care of the
rest.

A buffer is necessary for R-S decoding.

Isaac

[dizzy]

isw wrote:

Data buffering is used on newer models, including DVD players and MP3
compatible models. I don't think earlier CD models used it. So long as frame
sync is maintained within spec, the Reed-Solomon code takes care of the
rest.

A buffer is necessary for R-S decoding.

There's certainly always SOME buffering. It need not be the many
kBytes required for "skip proofing"