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Old 11th October 2012, 05:31 PM   #1
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Default Weird CD Player Problem

Hi folks, hope someone can help with this one:

Got a Denon DCD-835 which instantly reads CD's and also plays them, but every now and then it does something strange.

Around a couple of minutes into track 2 it "skips" (for want of a better word) back to the middle of track one. It doesn't do this all the time, just on some CD's.

It can also sometimes actually skip (usually in later parts of the cd), but this may have something to do with scratches on those CD's as it doesn't do this with all cd's.

I have had the lid off and cleaned the lens with isopropyl alcohol (99%) and regreased all the rails. I have tweaked CD63 KI's before (thanks guys on this site), so am not a novice, but I am a bit out of my depth as this seems to be intermittent. I can't really detect any bad solder joints either but have not checked all of them yet.

Any ideas what may cause this?

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Old 13th October 2012, 11:06 AM   #2
Mooly is offline Mooly  United Kingdom
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This sounds like classic symptoms of a sticky sled assembly despite you having greased the rails. A good test can be to connect a DVM across the sled motor. If the sled sticks the voltage will begin to rise before the sled jumps. Normally the voltage will be only a few 10's of millivolts as the sled motor turns a degree or two at a time.
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Old 13th October 2012, 11:32 AM   #3
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Aah, that would make sense, thanks, I'll check for that Mooly.

It didn't even occur to me that there are other bits in the sled assembly which may stick. I did move the sled by turning the cogs (to grease the rails) and it appeared to be running smoothly, alas, I will have another look at it and see if I can measure any rises in voltage when it happens.

I have never had one of these player before. Am quite impressed with the built quality. Just to start with it is quite heavy and there are a couple of extra separate power regs in there.

Dare I say it, it seems much better made than the old CD63, even.

Anybody out there have a schematic or diagram? May be worthy of some tweak attempts...
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Old 15th November 2012, 04:20 PM   #4
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Sorry for going on about this one but if anything, the problem's now worse than before.
This is what I have done so far:
Visually inspected the 3 pcb's for any loose solder connections, broken tracks and evidence of burning/ excessive heat-none.

The player has LM7805a and LM7806a on the power supply board which are attached to heat sinks and the sinks get quite hot (almost too hot to touch).

Have replaced the laser assembly twice, tried to do this with original Sharp/Sony units through ebay and each of those looks like it had an original Sony laser lens but the pcb etc was definitely spurious and chinese fake...

The last one came from the States and took 2 weeks to arrive-and turned out to be very badly made indeed.

However, it did work initially with an original CD.

After greasing all the rails (yet again) and cleaning the lens (yet again) I slotted it into my system...

Now it can not even play original CDs for longer than a few minutes before doing the following:

It seems to lose power for a fraction of a second (lens noise same as when powering the player up, i.e. trying to focus), then starts playing ok for a few seconds, then the same happens again.

This is driving me mad! I know this is a decent player wtf is wrong with it?

Help!
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Old 16th November 2012, 06:45 AM   #5
Mooly is offline Mooly  United Kingdom
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The next step has to be to look at the RF (eye pattern) and see if the amplitude and "general appearance" of the signal is good. That means a clearly distinguished "diamond" with little jitter. Amplitude is normally around 1.2 to 1.5 volts peak/peak on a normal CD.

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