Distortion/clipping, CD changer (Sony, 30 years old)

[mcovington]

I'm hearing distortion that sounds like clipping of the loudest notes when playing CDs in a Sony CD changer that is about 30 years old.  I have not yet traced the signal to see if it's in the CD deck or the amplifier, but strongly suspect the former, since the amplifier has worked OK with other inputs.  (I will double-check.)  Curiously, the problem was worst when the CD deck was first turned on, then diminished somewhat over a few minutes.  And it may be confined to one channel (not sure yet).

Does this sound like a deteriorating electrolytic capacitor which, perhaps, somewhat re-forms in use?   Other ideas?  Obviously, I need to signal-trace and find out where the distortion is coming in, but where should I look first?

[wasedadoc]

Confirm which of player or amplifier is responsible.  Then determine if one channel or both.

Doing the above and further troubleshooting will be much eased if you burn yourself a CD with test tones you can observe on a 'scope.

[mcovington]

Well, it turned out that cleaning the CD lens did it a lot of good.  Not what I would have thought, but on the latest try, the distortion was accompanied by a "whoosh-crunch-whoosh-crunch" sound that seemed to be at roughly the speed of the rotating CD.  I ran the lens cleaner through it and am not sure there is still any distortion.  There may be a little, and I'll continue to investigate.

[Martin72]

Hi,

I ran the lens cleaner through it

Lens cleaner ? Don´t say you´ve used one of these cleaning cds....
When it´s now "better", you´ve heard dropouts not distortion in the meaning of.
What player from sony, model name?

[mcovington]

Yes, a cleaning CD greatly improved the sound.  I heard both dropouts and distortion.  The distortion is still there to some extent.   Sony CDP-C365.  Curiously, the distortion seems to diminish with continued use, which makes me think it may be a marginal electrolytic capacitor slowly re-forming after not having been used in several months.

[Martin72]

Yes, a cleaning CD greatly improved the sound. 

From all cleaning attempts, a cleaning CD would be the worst solution.
It can scratching the laser lens..
Better use a cotton tip and some isopropanol, to clean (very gently) the lens.
If the dropouts still persists, buy a new laser:

https://www.ebay.com/itm/361554211982

[shakalnokturn]

SMT electrolytics on small PCB under the pickup?
Maybe worth checking spindle motor for poor commuter contacts or partially shorted winding.

[coromonadalix]

most likely the laser pickup itself, the lens suspension could have finally died

since you don't give the model, its hard to guess,  some models where all plastic, and  the lens would go down inside the pick up assembly, it will be harder to make some focus ok and read the disk ...  and you need a crafted cd and a scope  to check if it's really the cause

it could even be the suspension system who's failing,   they where made with soft rubber with an special grease inside them, over time they harden and don't do their job anymore  ...


Funny to see lots of people saying it's always the capacitors ....  i have repaired tons of theses cd changers and it was always a mechanical problem  loll

And 30 years it had a very good life  loll 

Now it's usb key with tons of music ...

[Martin72]

since you don't give the model

He did, see my last post.

[coromonadalix]

ok  its an kss-240a  pick up assembly      changed a lot of them,  lots of kss-210 too, i'm surprised  it last that long  loll

You can do a visual inspection, if with an cotton swab, you sligthly push down the lens and if there is no down movement, you need a new one, it is supposed to float  at mid air position (moving up and down)

normally  when you close the rotating platter,  the unit is supposed to scan the position, and you should see the lens moving up and down,  the cd will not spin until the cpu knows there is a cd rom  and will do an TOC (focus ok  if i may say)

The service manual with adjustments and or  checks are easily found,   but you will need a scope

[mcovington]

The drop-out problem seems to have cleared up, although I will check those things.  There remains definite, reproducible distortion on the peaks of high-level audio.  We noticed this on a couple of recently acquired CDs that have loud peaks with clear-toned instruments where one would not expect a fuzz sound (e.g., Rick Wakeman playing the piano), and the distortion on the peaks is not present when the CDs are played on other players (I even decoded one of them into a waveform with Audacity; no clipping on it). 

I will check a number of things.  Any other suggestions?

[coromonadalix]

With such a technology gap   you may or could have some problems, and you say it doesn't do that on other players ...

You do know that player is a basic one, it's not like the sony high end stuff with more advanced dac's  etc ... and the recording technology used, DDA DAA  etc ...

Anyways  I have given you some ideas, and the service manual will help on some cases, they are free to download


Without being rude,  it may be a time to let it rest ??     A laser pickup is around 40-50$  and you have to do some alignment too  ....

Good luck


I still have this one from 1980 era : https://www.cassettedeck.org/sony/tc-k81

And this one is unkillable ... with life time heads,  still work a threat today, only costed me a pinch roller kit and belts, i have a tape collection of jean michel jarre on them, and the noise floor is really low, incredible sound  with well preserved / stored chrome tapes,   but like everything   there is some limits

I even have the same albums on cd's,  and i hear the sound difference ...

[mcovington]

We are indeed thinking of replacing the whole unit.  I don't remember how long we've actually had this one, but the service manual has a 1995 copyright date, so I'm thinking we've had it at least 20 years.  Time for a new one.  My day job pays well enough that I don't want to take much time away from it to do an extensive repair and adjustment session.

[Haenk]

Maybe try digital out and analog out (digital out obviously some external DAC, a lot of amplifiers have those built in). If the external DAC still shows oddities, it's in the pickup or digital part. If it's only in the analog output, you need to check there.

[David_AVD]

Occasionally I've seen really old amplifiers with line level inputs that are overloaded with the generally much higher line level outputs that CDs have.

Adding a simple resistive divider on the input used for CD solved the issue.

[MathWizard]

most likely the laser pickup itself, the lens suspension could have finally died

since you don't give the model, its hard to guess,  some models where all plastic, and  the lens would go down inside the pick up assembly, it will be harder to make some focus ok and read the disk ...  and you need a crafted cd and a scope  to check if it's really the cause

it could even be the suspension system who's failing,   they where made with soft rubber with an special grease inside them, over time they harden and don't do their job anymore  ...


Funny to see lots of people saying it's always the capacitors ....  i have repaired tons of theses cd changers and it was always a mechanical problem  loll

And 30 years it had a very good life  loll 

Now it's usb key with tons of music ...

I tried to repair a similar era Sony 5 disc changer, with a MCU problem. As a precaution, I checked all the electrolytic's, and they all still had great ESR and 1kHz tan_phi or whatever. And the PSU is on all the time it's plugged in. And as far as I know, it was left plugged in most  of the 25-30 years.