CDM4/19 skips - diyAudio
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Old 17th November 2010, 11:19 AM   #1
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Default CDM4/19 skips

Hi,

I have a Marantz CD40 which started skipping a while back and has got progressively worse. The PCB is a Marantz/Philips board that is used in many players. I had a CD40 previously that needed adjustment and I found pictures posted by rbroer november 2004 at the link below showing where to measure and adjust 2 pots. I saved this to favourites but now that I need it, it won't open.

Can anyone explain where to measure. The 2 pots 4K7 and 22K set up 50mV and 400mV across some resistors but without the picture I have no idea which ones they are.

My original CD40 was 'lampized' and sounded really good. I then converted it to NOS and it improved further. Was happy with this untill it was stolen. I was about to mod my next CD40 but need to get it to play correctly first.
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Old 17th November 2010, 11:32 AM   #2
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Sorry forgot the link.

http://www.diyaudio.com/forums/digit...tment-cdm4.htm
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Old 17th November 2010, 04:17 PM   #3
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I think this is the thread, but the pictures are gone...

How to make correct adjustment of CDM4

w
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Old 17th November 2010, 04:45 PM   #4
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How does the fault present itself?

The problem could also be mechanical...

Cheers!
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Old 17th November 2010, 04:50 PM   #5
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Actual skipping on a cdm4 is usually caused by wear in the disc clamper's plastic "bearing" surface. If you very lightly feel the clamper will cd is playing, you'll likely feel a 'bumping' with each rotation, as the little ball bearing goes in & out of a dimple it has worn into the clamper. Solution is to simply re-flatten that clamper surface, either by very fine sanding, filling with pc7 epoxy & sanding, or by just adding a thin overlay of a hard, smooth material. And don't forget to grease it with a fairly thick grease.
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Old 17th November 2010, 06:42 PM   #6
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Skipping that gets worse over time has always turned out to be caused by dust contamination of the lubricants used for the head positioning mechanism, in my experience. I have cleaned and re-lubed at least three different CD players and have cured the problem in every instance.

I am pretty sure it is dust, because the problem would arise about every two years in my players when I lived in Australia. Since moving to Ireland, the frequency of needing to do this job has dropped to once in 6+ years.
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Old 17th November 2010, 09:03 PM   #7
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Quote:
Originally Posted by cheapskate View Post
Skipping that gets worse over time has always turned out to be caused by dust contamination of the lubricants used for the head positioning mechanism
That's true for 3-beam pickups which use a worm gear drive to position the head, but the CDM4 is a single-beam pickup using a swing-arm and dust is unlikely to be the cause of skipping.
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Old 18th November 2010, 05:09 AM   #8
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wakibaki : Yes that is the correct thread and its those very pictures I was after.

Scorpio : Some CD's play better than others. It might play the first 2 tracks then skip a bit then play then skip and get hung up. The player is also fussy and simply will not play some CD's at all, mostly home-copies.

stephansank : thanks, had not thought to check the clamp.

cheapskate : I have cleaned the laser and anything else that moves but no luck.
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Old 28th November 2010, 10:00 AM   #9
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Default cd40 skipping

Quote:
Originally Posted by stephensank View Post
Actual skipping on a cdm4 is usually caused by wear in the disc clamper's plastic "bearing" surface. If you very lightly feel the clamper will cd is playing, you'll likely feel a 'bumping' with each rotation, as the little ball bearing goes in & out of a dimple it has worn into the clamper. Solution is to simply re-flatten that clamper surface, either by very fine sanding, filling with pc7 epoxy & sanding, or by just adding a thin overlay of a hard, smooth material. And don't forget to grease it with a fairly thick grease.
Hello all,
sadly I, too, belong to the skipping mechanics club, with my cd40 (my cd94 has another fault, it stopped reading/spindling at all).

I'm not sure I got properly stephensank's advice. I miss which is the clamper surface which should be reflattened. Yesterday I added a small weight on the top of the clamping mechanism. I seem the laser reads properly, and was guessing the cd is sliding on the spindle...

Thanks for advices,
Stefano

P.S.: May the or part of the reason aging psu electrolytics?

Last edited by seppstefano; 28th November 2010 at 10:10 AM.
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Old 29th November 2010, 01:26 AM   #10
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On top of the CD is a big plate that holds the top clamping hub to keep the CD tight to the platter. There is a small(too small) steel ball bearing in the top of this hub that is pushed down upon by the big clamping plate. It is the small surface that is pressing down on that steel ball which is the place where you will find a small hole caused by the grinding of the ball against it. This must either be very finely flattened/smoothed & re-greased, or the alternative is to clean that surface & glue onto it a thin teflon or other smooth & tough plastic sheet material, with a thick grease then applied, to make a new 'bearing surface' for clamping against the steel ball. Much easier than smoothing the old surface, if you can find a suitable bit of teflon or etc.
Old electrolytics(those that are not Nichicon brand) can absolutely be a problem, but not one that causes skipping.
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