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sadim1223 22nd March 2009 08:21 PM

CD player won't play clear disks
 
I got a vintage Akai cd-a30 as a hand-me-down. The cd player sounds great, except for the fact that if i put in a disk with a non-clear center area, the CD player refuses to play and simply displays a "--" on the display. Btw, if i put in a cd with a clear center area (the overwhelming majority of my disks) the motor doesn't even turn. I opened it up and there does not appear to be any additional sensor besides the lens in the CD mechanism. Any thoughts? Thanks

-Sadim

sadim1223 22nd March 2009 09:02 PM

i'm further confused. The cd player is currently doing a FANTASTIC job of working though a CD-r with a clear center. It also played the clear-centered "Horowitz-Favorite Chopin" without any problems. I tried covering up the middle of one of the clear-centered cd's which will not play with black electrical tape which did not help. I guess this has nothing to do with the color of the insert.

Any thoughts as to why certain CDs will play while others will not? Also, does anyone have a manual/schematic for these? Should I be looking at changing the caps? It was manufactured in 1985. I took the cover off and things are very tidy. Thanks

-Sadim

analog_sa 22nd March 2009 09:12 PM

I would imagine that an '85 laser can be quite selective into what it can or cannot read. Nothing to do with the transparency of the center area. Have you tried cleaning the lense?

Steerpike 22nd March 2009 10:39 PM

If the disc wont rotate at startup, that indicates a failure to get a focus servo lock.

In the case of some of the Philips mechanisms, for instance, the thrust-plate that the spindle motor shaft rests on wears over time, making the turntable sit too low, then the player cannot focus on some discs.

I'm not saying it shares a Philips mechanism, but it might suffer from a similar sensitivity. Check if it has a disk height adjustment.
Sometimes cutting a circular 'washer' of adhesive paper and sticking it to the reflective side of the disc, to lift the disc off the turntable by a few mils, helps to confirm this diagnosis.

Otherwise, a general tuning of the focus servo adjustments may be in order. Otherwise it may be the laser has aged, and doesn't like the less reflective discs in our collection. (Be careful about messing with the laser power adjustment if you dont have the correct service info - you can shorten its life severely by misadjusting it.)

My '84 Sony and '84 Philips both still play ANY disc.

sadim1223 23rd March 2009 04:07 AM

steerpike,
it is in fact one of the many philips mechanism players. Should I adjust the height if it plays other CDs? Is there a decent guide online as to how to go about this?

Also, can you elaborate by what you mean by a general tuning of focus servo adjustment.

thanks for the replies.

-Sadim

Steerpike 23rd March 2009 09:26 PM

Well the height problem can make it picky about which discs it will play.
There are lots of online free service manuals, but first you need to identify WHICH mechanism you have. Post a photo and someone somewhere will identify it for sure.

Corrrect adjustment requires at least an oscilloscope, but its an easy thing to do. Unless you can *see* the waveforms, its a hit and miss affair.
An oscilloscope also lets you see if the laser is still good (check the amplitude of the RF eye pattern)

As the player is old, it may have gone out of alignment - that's why I suggest general tuning - or checking - of the servo adjustments, such as offset and gain.
More importntly - if anyone else has been poking around inside it, you have no idea if they messed up the adjustments (this includes some so called qualified service technicians!), so it is prudent to do those adjustments yourself - then you KNOW they are correct.

poynton 23rd March 2009 11:30 PM

Quote:

Originally posted by sadim1223
steerpike,
it is in fact one of the many philips mechanism players..................


Interesting...

I thought the majority of Akai players used a Sony pickup.

Andy

sadim1223 24th March 2009 05:57 PM

i read somewhere that it was philips. I'll open it up later when i am home from work.


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