Denon CDP not reading discs - diyAudio
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Old 5th April 2009, 02:27 PM   #1
Rmanen is offline Rmanen  Netherlands
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Arrow Denon CDP not reading discs

I have recently acquired a Denon DCD-755AR cd player, I got it for free as the previous owner claimed it was broke. I hooked it up at home and grabbed a pristine cd, and it worked only halfway through the song it stopped, readjusted the laser and went on for a few seconds longer.
It won't read anything less than perfect scratch free discs, it won't even recognise the TOC.

The above leads me to believe it works fine, the laser just needs to be "calibrated".

I opened it up and the focus and tracking gain/offset trims are easy enough to find, however the service manual/datasheet is not.

Can anyone help me with either the manual or the required setting of the trimpots? There are 2 pin headers near the trims, which I think are test points. However without knowing what to measure where, I'm a bit stuck.
THX, Rob
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Old 5th April 2009, 05:41 PM   #2
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Before you start tweeking the adjustment pots, I strongly suggest cleaning the laser lens, the slide rails, and the gears.
Also, don't lubricate anything, it won't help. I have a DCD 815 thats been working fine for about 13 years with only occasional cleaning.
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Old 5th April 2009, 07:18 PM   #3
Rmanen is offline Rmanen  Netherlands
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Ok, what shall I use to clean the lens? a cotton swab with dishwashing liquid?
I checked the gears, and they don't seem gritty, so I think that isn't the problem.

I had a Denon DCD 810, I absolutely loved it, it broke while moving house sadly
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Old 6th April 2009, 10:39 AM   #4
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I use a cotton swab lightly wetted with a good quality glass cleaner, then carefully wiped with a dry swab. I've also tried isopropyl alcohol, but it dosen't seem to work quite as well as glass cleaner. Be carefull to not use too much pressure on the lens assembly, they are pretty fragile.
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Old 6th April 2009, 05:42 PM   #5
Rmanen is offline Rmanen  Netherlands
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Just now I have cleaned the lens assembly with some lab-grade ethanol (aka 70% alc.) and so far it has slightly improved playback with my pristine test-cd (Marcus Miller - Free). Before it skipped/readjusted itself several times per song, and now it skipped once or twice... time to check out the copied cd-r's and an old cd....

Shame, the "old" cd (REM - Automatic for..) doesn't start, it does read the TOC though. When i try to start from track 2, it starts and plays pretty good. Still the occasional glitch and even a few full-stops though, its not quite there yet. Time for a CD-R.

Auch, it doesn't even recognize a properly burned cdr... I'll check another "old" disc.

Up for testing in this final round is Dream Theater's Six Degrees of Inner Turbulence, and as I close the tray it starts to play immediatly! However this excitement is only short lived as after 15s it skips a full minute ahead, (during the first 15s I could hear the laser trying to "lock") and after another 10s a full-stop.

It appears the cleaning has helped somewhat, its just not quite there yet. How should I proceed?
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Old 6th April 2009, 09:56 PM   #6
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Coax it to play something - anything - and then adjust the servo trimmers while listening to the mechanism, not the audio.
You can hear when a CD mechanism is correctly aligned - although it might be something you need a bit of practice at identifying.
If you're not sure what to listen to, you can always nudge the trimpots slowly in either direction & see if that makes it skip less (or more).

You should NOT adjust laser current by ear! More laser current than is necessary doesn't sound better & just destroys the laser, quickly.

Some players NEVER read CDR reliably, even when perfectly aligned.
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Old 8th April 2009, 11:12 PM   #7
Rmanen is offline Rmanen  Netherlands
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Quote:
Originally posted by Steerpike
Coax it to play something - anything - and then adjust the servo trimmers while listening to the mechanism, not the audio.
You can hear when a CD mechanism is correctly aligned - although it might be something you need a bit of practice at identifying.
If you're not sure what to listen to, you can always nudge the trimpots slowly in either direction & see if that makes it skip less (or more).

You should NOT adjust laser current by ear! More laser current than is necessary doesn't sound better & just destroys the laser, quickly.

Some players NEVER read CDR reliably, even when perfectly aligned.

I'm getting there, as now the player plays all 3 of my aforementioned test discs. It does still skip though, so I'll keep on working those pots
In the mean time, any advise for improving the tracking problem besides the pot adjustments by ear?
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Old 9th April 2009, 12:33 PM   #8
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Try putting a few small pieces of adhesive tape (one layer of masking tape) around the CD hole, on the mirror (read-out) side. This is a test to see if the following is an issue:
On some mechanisms - especially the original Philips types - the spindle shaft thrust plate wears down; then the CD sits too low in the mechanism - too close to the optics - and the focus servo cannot compensate for that. The correction is a mechanical adjustment, not an electrical one.
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Old 28th April 2009, 01:54 AM   #9
Rmanen is offline Rmanen  Netherlands
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Been a while, still busy though.

Anyway, the problem turned out to be a combo of all of the above really, only I seem to have busted the loading mech.

Its a Sony KSL2130CCM, but i can't for the life of me find a supplier... anyone know any?? Please help, as its incredibly frustrating to get it to work only to find I wrecked it
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Old 28th April 2009, 04:41 PM   #10
guido is offline guido  Netherlands
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Is it similar to a DCD800? Have one available.

mvg,
Guido
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