Audio CD player "uneven" sound

Couldn't that only happen if the clock frequency slowed due to a faulty crystal or loose loading cap or related fault.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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

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.

but

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.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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

the

you'd

the

anymore.

wire,

way

When I've some time I'm going to mod one in such a manner just for fun. So to re-cap, to the OP, then a faulty crystal could lead to the observed effect ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Yep, that's my feeling.

Arfa

Sometimes we also see simple bad solder connections at the crystals...

Mark Z.

That's a fact, Mark - particularly since the manufacturers have been forced down this nonsense lead-free path ...

Arfa