disc recognition problem

[elaar]

Hi, i was just wondering if anyone knew what the "usual" cause of a cd player to not read/recognise any CD is? I haven't mentioned any specifics because i now have 4 cd players that refuse to do this.

Any advice gratefully received,
many thanks,
Alex

[singa]

The laser is going out ( most of the time) or a dead spindle motor.

[anatech]

Hi elaar,
It depends on the transport. Clamper bearings in addition to what singa mentioned.

In order, clamper bearing (unless magnetic), disc motor, servo component (Philips it seems) and finally laser head.

Move adjustments to the top of the list if some has been in there. With earlier Pioneer units the lens can fall off the pickup ( ) and sometimes its just cooking oils or smaoke on the lense.

-Chris

[mrshow4u]

If the disc spins right away, the player has sensed FZC (focus zero cross) and will spin after that. When it spins, if the disc motor seems noisey, it might be going out. If these are older players and you're trying to play a CD-R, you probably won't get very far. Older players seem to have a tougher time trying to get a good eye-pattern out of discs with poor reflectivity (CD-R's). If it does spin, you can check the quality of the eye-pattern. Use as high a bandwidth scope as you can get. Hope for 60 MHz, or better. Look for a testpoint (+ground) labled "RF" or "EFM". Adjust the time scale until you see a waveform with diamond shapes in it. Adjust the scope trigger until the focus looks best. Now, two things to look for: 1) is the pattern fairly clear? Is the amplitude pumping? Try with several discs. If the pattern is not fairly clear, or the amplitude seems to be squashed with lots of double images on the lines, the laser might be weak. You can try to clean the final optical lens (carefully), but that's really all you can do. 2) If the waveform seems to be compressing and expanding in time, the disc motor is going out. Either the bearing, or the brushes. Same fix, replace motor. If you replace the motor, and the replacement motor doesn't include the turntable, carefully make a measurement before dismantling. Put the turntable on the new motor carefully. ....don't bend the motor shaft.

[elaar]

Hi,

many thanks for the detailed and useful replies. How about when the tray refuses to open? I'm guessing it's either the motor, the belt (do they have belts or are they all cogs?) or the actual control circuit. Is it rare for it to be the circuit (making it a much more difficult fix i'm guessing)?

Many thanks,
Alex

[anatech]

Hi Alex,
Tray problems usually come down to a belt that is slipping. I have seen broken gear teeth, but that is rare these days. Dirty limit switches may also cause these troubles.

For observing HF patterns, the new 20 MHz scopes are fine. You do need a 0.5 uS / Div setting for the horizontal time.

You wil need to troubleshoot one at a time. Tell us what equipment you have and make & model of the unit as we start.

-Chris