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Old 24th November 2007, 03:12 PM   #1
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Default Skipping NAD 5000 CD player

Hello,

I've just discovered these forums after searching around for information on repairing a NAD 5000 CD player.

From what I've gathered I probably need to change and/or adjust the laser pickup (a KSS210A I believe), but would like an opinion on the symptoms I've been experiencing first.

In short, the player will skip and sometimes just lose tracking and stop, BUT this typically happens only on the first tracks of the disc. Once it is past those tracks, it plays fine. I also noticed that certain specific CDs are prone to this problem, while others are not (all are pressed CDs).

Does this sound like a typical aging laser diode? Should I try tweaking with the potentiometers (VR101 to 105) first? One thing I noticed is that the motor spins faster when playing the first tracks... could it be an aging motor that can no longer spin fast enough for reading those tracks?

I would appreciate any suggestions. Many thanks!
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Old 24th November 2007, 05:55 PM   #2
Mooly is offline Mooly  United Kingdom
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Hi,
First off, don't adjust any pots unless you know the correct set up procedure. CD,s do not spin at a constant speed but vary from around 400 rpm at the start to around 200rpm at the end.This is called constant linear velocity or C.L.V. I guess from you asking this that you are not familiar with the technology.All is not lost however, first is the lens clean.If that's O.K. then yes a faulty pickup is quite likely BUT there can be other problems as well.The spindle motor can suffer with wear.Can you feel any play in the bearing.If you have a go at replacing the pickup it should be O.K. without any setup.New KSS210 have a blob of solder across a "shorting pad", to be removed when fitted.Here in U.K. new pickups are around 10.Don't pay over the odds for a Sony branded part etc there are plenty of good quality compatible parts around.Another trick you can try with the spindle motor to help confirm if the moter is "electrically worn" is to unsolder it and then apply a 9Volt battery across it to try and burn off any contamination on the commutator, bit of a bodge but it can work to prove a point.
Regards Karl
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Old 24th November 2007, 07:53 PM   #3
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Thank you for your reply.

I understand the difference between CLV and CAV in computer optical drives but wasn't sure how audio CDs are actually read, thanks for the clarification.

My thinking was indeed that since the player only has problems reading the first tracks which require higher rotational speed, perhaps it was the spindle motor and not the pickup that was deteriorated.

I also should have pointed out a few things beforehand.

1) I already tried cleaning the lens, it had no effect.

2) I did find another thread here about replacing the pickup on this exact same model:
Nad cd 5000 : replace laser pickup

3) And I found these sources on adjusting the pots:
http://www.diyaudio.com/forums/showthread/t-77734.html
http://www.delarte.nl/index.php?opti...d=15&Itemid=37

I checked the spindle motor as you suggest. By trying to wobble the spindle gently, there is no play at all except along the longitudinal (or vertical) axis.

What do you think the likelihood of a bad pickup vs bad motor is given these symptoms?

And thanks for the tips on the pickup - I found a good price on eBay but it was not Sony branded and I wasn't sure whether it would be good quality - now I know.

Regards
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Old 25th November 2007, 07:09 AM   #4
Mooly is offline Mooly  United Kingdom
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I would certainly try a new pickup.I used to order these by the dozen (really) around 12 years ago, when I worked for large service company.Many music centres were a favorite for failure with the C.D. unit fitted at the top where all the rising dust collected.The suspension unit in the lens assembly can also suffer with wear.My point about the battery and the motor is this, the commutator can be worn/contaminated and this can effect the ability of the servo to lock correctly.A good check is to use an oscilloscope across the motor terminals and look at the "ripple" voltage.The 9 volt battery helps cleans off any contamination, but always unsolder at least one wire first.As for adjustments EF balance is most critical and can only really be set with scope.If you do adjust mark each pot with felt pen first so it can be put back.Tracking gain and focus gain are suprisingly non critical in the real world.The last 3 digits of the serial number on laser are the value in milliamps of the laser current as set at the factory. E.G xxxxxxxx567 is 56.7 milliamp.There will probably be a resistor on the main PCB where you can measure the volt drop across it and calculate the current.If higher than 15% or so laser deteriorated.The laser diode has an integral photodiode on the same die and is used to monitor actual "light" output.An automatic power control will keep increasing the current as the laser wears to maintain this output.
Do you have access to any test equipment?
Best of luck let us know how you get on.
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Old 26th November 2007, 02:04 AM   #5
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Thank you very much for all the valuable info. Unfortunately I don't have a scope at home, but I do have a proper multimeter.

I believe I'll try your two suggestions first: see if I can find a resistor to calculate current through the diode as a diagnistoc test (found a copy of schematics for a nearly identical model), and apply a 9V battery to the motor. Based on the results I'll decide whether to pursue and replace the pickup or use this as a pretext for an upgrade. I'm a little concerned that it might end up being more complex than I anticipated. I found this other thread with someone else that has a player skipping on first tracks, and replacing the pickup didn't solve his problems: Arcam alpha 7 CD - replaced laser but still skipping..

Will let you know how it turns out.

Thanks again!
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Old 27th November 2007, 10:15 AM   #6
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Lubricate the spin motor and then check. The problem might be solved or reduced.
If so change the spin motor after knowing the intricacies.

Gajanan Phadte
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