Marantz CD67 error correction digital output - diyAudio
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Old 2nd October 2013, 06:37 AM   #1
jpprins is offline jpprins  Netherlands
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Default Marantz CD67 error correction digital output

Years ago I modded a CD67SE with good result. Lately however it have developed a strange defect. There is no, or only bad error correction over the digital port (connected to a DAC); I hear every speck of dust and scratch. (Its on the cd for it is audible on the same spots if replayed)
But, over the analog ports it plays fine!
It might be the DAC, but if I play a cd on my pc with the same DAC on the SPDIF port, it sounds fine.
I know, I should find another real cd-player to test the DAC, but that is not easy for me at the moment.
I found the service manual, and that gives me the impression there is error correction in the SAA7372, before the signal is converted to analog.
The player gives no error codes, and I have cleaned the lens.
Anyone any idea what can cause this?
Regards!
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Old 2nd October 2013, 06:42 AM   #2
Mooly is offline Mooly  United Kingdom
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If its OK on analogue out then it could be the external DAC or a slight mismatch in CD and DAC clock frequencies. Also if using coax rather than optical then there could be a level issue that's developed. Hard to say for sure without more detailed testing.
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Old 2nd October 2013, 09:31 AM   #3
DF96 is online now DF96  England
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Error correction is so built-in to the de-interleaving and decoding logic that it is difficult to imagine how it could be disabled. It may be that somehow you have invoked an engineering test mode which passes semi-raw data through. Just a guess!
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Old 2nd October 2013, 09:16 PM   #4
jpprins is offline jpprins  Netherlands
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Thanks for the comments!
I managed to get another cd-player with a digital output and I'm sure now that my external DAC is okay.

Now, I see the 67 has 2 clocks (at least, are there more I missed?); one 8Mhz clock for the whole digital part en another 16.9344Mhz for the internal DAC, which seems to deliver good sound on the analog port. (I swapped it long ago for a TentLabs XO, before I got an external DAC)
So can it be this 8Mhz clock is slightly faulty? Causing the chips to generate a spiky signal on errors. Too bad for the external DAC, but good enough for the internal one to create a reasonable signal? In that case I'd solder in an other 8Mhz crystal.

I see in the manual nothing about test modes. Just that service mode is canceled when the player is turned off.
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Old 3rd October 2013, 07:56 AM   #5
Mooly is offline Mooly  United Kingdom
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If the clock (and it can be either DAC or player related) is slightly out of the "pull in" range then you can get this kind of effect.

Try some typical engineer tactics to narrow it down

If you put your finger on/around/near the oscillator crystal and its components does the problem dissappear (or go worse) ? What you are doing is pulling the frequency slightly one way or the other. You need to do that to the DAC as well as the player.

Beyond that and you really need dedicated test gear to check out the frequencies and levels.
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Old 3rd October 2013, 04:04 PM   #6
jpprins is offline jpprins  Netherlands
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Ahhh.. That engineering tactic did narrow it down, but its not the clock.
If I lay my finger gently on the plastic that houses the laser, effectively damping it, the noise is gone, and if I lift my finger, it is back.
So a new laser mechanism is in order I suppose.
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Old 3rd October 2013, 04:15 PM   #7
Mooly is offline Mooly  United Kingdom
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Thats a surprising result tbh. Do you mean you are slightly "slowing" the disc ??? by touching the platter clamp or just touching the general "fixed" or non rotating parts. If the later then it suggests that the RF signal from the pickup is marginal. Again, the real diagnostic is to put a scope on it to see what the quality and amplitude are like. Have you cleaned the lens ?
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Old 3rd October 2013, 04:35 PM   #8
jpprins is offline jpprins  Netherlands
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No, no, I'm not slowing the disc, just touching gently the black stationary plastic with houses the laser, just behind the rotating disc. I feel I'm damping its vibration by doing so.
I did indeed clean the lens, with both a lens cleaning cd set which utilizes cleaning fluid and with a can of compressed air. Cant get it any cleaner without touching it with lens paper or a cloth which I am still loath to do at the moment.
But there is no difference in SQ between before and after.
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Old 3rd October 2013, 06:00 PM   #9
DF96 is online now DF96  England
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Capacitor gone in a laser positioning servo loop?
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Old 3rd October 2013, 06:11 PM   #10
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by DF96 View Post
Capacitor gone in a laser positioning servo loop?
Hmmm, I doubt it would be anything so deep seated tbh. I think this uses the CDM12.1 ? pickup (or so a quick search tells me). They are cheap and easy to replace.

It is still worth cleaning the lens properly. Use a good quality cotton bud but tease the cotton out at the end ever so slightly. Moisten (not wet) the bud with fluid and gently clean the lens. Use a torch to look at the surface and make sure its really clean.
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