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Old 21st December 2012, 03:51 PM   #51
nuryev is offline nuryev  Australia
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I tried the freezer spray on various components including ICs on the pcb and the change in temperature did not result in any audio output.

Your question: "When you say that the audio cuts out, do you mean that the player continues to track the disk? Does the display show progress through the disk as if it were playing"
Answer: During play, the cd will play as per normal, toc timer track recogntion etc. And audio. But this will go on for approx 10 - 15 minutes the audio will cut out. Cd continues spinning, timer continues and the laser mechanism can be seen to be moving toward the rear of the tray ie it is not fixed or 'stuck' on any tracks.
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Old 21st December 2012, 06:21 PM   #52
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Lets try and look at this from another angle (and I'm saying this because without actually seeing for myself exactly what is happening its all becoming a bit guess work)

The TOC advances correctly and the player "seems" OK apart from the audio dropping out.
A player where the RF has a problem causing the audio to stutter and yet the TOC to work is a knife edge situation, so is it probable or likely that is happening. Lets say no. What are we left with. Without hearing and seeing the fault, again its guesswork but harsh "digital" sounding hash is often caused by faulty DRAM memory (in older players) but I've never had the problem on the combined DAC/MEMORY/PROCESSING chips. Doesn't mean it doesn't happen though.

As a totally off the wall suggestion try disabling the audio muting in the analogue stages and see what that does.

I think beyond this and we have to accept that its not a diy prospect without the right test gear and so on.
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Old 21st December 2012, 07:36 PM   #53
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Apologies for repeating Mooly...written so sending anyway.

At the start of the thread, there was some skipping and response to tapping the mech. Have these aspects disappeared?


I'm still trying to learn about this stuff and my experience is of machines a generation before yours, so I might be wrong...


Your mech must be focusing and tracking otherwise it couldn't do what it's doing, music or not. Further, the signal from the HF amp to the decoder (that should appear as the eye pattern) must be good enough to decode for the player to navigate itself. The music data and the subcode are read from the disc, carried on the same signal, and decoded by the same decoder chip.


One thing you can check easily with a multimeter is the mute signal.


Without a scope, I would use a CD with a simple signal such as a full-scale 1kHz sine wave, assuming the machine can read CDRs, so then I could follow it back through the audio stage with the meter set to AC volts, looking at the output of each opamp, and the DAC if it's voltage output. When the audio is working and when it's not.

If the output from the DAC (or the I/V stage) disappears, then you are left with the decoder chip, the digital filter, or the DAC. I would check for cracked pins or poor solder joints, but they can be hard to spot even with a magnifying glass. Others may be able to comment on whether the health of digital signals can be interpreted with a multimeter. Tricky, I would have thought.

15 minutes is a long time. For it to be heat related, it would have to be somewhere that gets hot very slowly, and only in the presence of audio. An encapsulated class B audio stage perhaps, or it's power supply. Does it just vanish, or fade, or what? Intriguing, don't give up.
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Old 23rd December 2012, 10:35 AM   #54
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by PlasticIsGood View Post
I'm still trying to learn about this stuff and my experience is of machines a generation before yours, so I might be wrong...
This might interest you as a general guide to working through a problem,
Sony CDP790 and KSS240 Restoration Project
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Old 23rd December 2012, 03:08 PM   #55
nuryev is offline nuryev  Australia
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Update on the challenge guys...

First off, don't know how to disable the muting on the player - but i think part of the mods required attention to the muting section. or disabling it ( I do know that I have to turn the cdp on first and then the amp) to prevent a popping sound..

I had a think about an alternative approach while still trying to source a scope again.

The uneducated logic being - if i use an external DAC and the fault disappears then it is the audio/dac section. If the problem is still evident with an external DAC then the problem may well be the laser pick up. ( I am aware that it may be more complicated than my description). However, I tried the coax to an av amp and this did not work at all - the word DISC was displayed, no spin up and no TOC!!!
I removed the coax and powered up and the cd spun and toc display popped up immediately.
OK! is the problem linked to Coax?? Too difficult to consider..

So I moved to the next option (Optic output option) plugged into my AV amp and it played BUT while the cd produced audio through all the tracks - however, it produced shorter audio output times ie played for 10-15 seconds and audio dropped out for a second or second and a half and audio kicked in again and this went on for about 25 minutes or 5 tracks then audio cut out altogether. I switched back to analogue and the same problem persists ie - plays for 10 -15 mins drops out completely then after 10 mins continues playing -

This is interesting - with analogue output - audio plays for 25minutes and drops out completely. Using the optic output, the audio dropouts were more frequent and significantly shorter, with audio continuing after 1.5 seconds or less. We may have to rethink the heating possibility.
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Old 23rd December 2012, 05:38 PM   #56
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Good thinking to try an external DAC.

The coax thing is really odd and I wouldn't expect that to happen. Only two possibilities there, one is that the coax feed is unbuffered (surely not) and connecting it to the DAC kills or reduces the level internally in the player such that it throws a fit. That the coax feed should be configured like that is too unlikely to contemplate... although you mention mods haveing been done. The other thought which is even more unlikely is that there is some bizzarre short occuring via the coax and the equipment grounds.

Normally the coax feed of the SPDIF signal is via a tiny "pulse" or HF transformer to make it imune to whatever the "customer" connects or does to the output. I would have to see the circuit to see how its configured but what you describe sounds totally odd. I would say that was worth investigating.

The optical output vs the analogue output differences may just be down to the different signal processing each DAC uses and when it sees fit to mute the audio. I wouldn't read to much into that other than it seems to point to a front end problem.
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Old 23rd December 2012, 07:58 PM   #57
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Helpful, thanks. Knowledge is social, and it's reassuring to see that my rather isolated efforts to learn aren't so far away from professional practice. I'm impressed by your twiddlesticks. Having fixed quite a few early players since arriving in the digital era this year, I just had my first accident, blowing up a CD50 with a screwdriver.

Compared to Philips single beam mechs, Sony and Philips CDM12 machines seem very fidgety, and get mechanically noisy, apparently beyond the range of adjustment. Ringing, over-hard plastic doesn't help. It's a pity Sony doesn't explain the "correct" method of adjustment. Presumably it allows the system poles and zeros to be optimally spread. I find the two nested subsystems for tracking control hard to get my head around.

Returning to the matter in hand, I think we're stumped for lack of data. If the problem's not in the audio section, then without a scope I'd be doing what I like least: patiently logging the DC and AC voltages on lots of pins. The cause of completely lost audio should be obvious somewhere, if the machine is otherwise working normally.
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Old 23rd December 2012, 09:17 PM   #58
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Yes, good idea to check the digital out.

The audio mute signal should be quite easy to find and very easy to check. It goes to the mute section and changes state before and after each track. I assume you have a circuit diagram?

If the machine has a chip that combines digital filter and SPDIF encoding, I would check around there, especially if the circuit has been modified, obviously. It could be that the modification has caused, or is causing the problem, by overheating part of the chip or its power supply, or upsetting its clock.

It seems to me more likely now that the problem is about failure to process the digital signal, rather than a rogue mute signal. AFAIK, everything up to and including the decoder has a part in controlling the mech, so if the mech is well behaved the problem must be after that, and before the encoding of the digital output. There's only the filter chip, unless an improper system microcontroller is intervening very strangely.

Mooly, what's a "front end problem", and what points to that? Can it intervene in such a way as to generate a mute signal that goes to the digital output?

An overheating chip may degrade the signal in a way that is interpreted differently by each system. Something must be responsible for explaining the timing of each transition from on state to another.

Hoping I'll be in sequence this time....
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Old 24th December 2012, 06:45 AM   #59
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Quote:
Originally Posted by PlasticIsGood View Post
I'm impressed by your twiddlesticks. Having fixed quite a few early players since arriving in the digital era this year, I just had my first accident, blowing up a CD50 with a screwdriver.
Good aren't they I have a "proper" diffraction grating adjustment tool for some pickups too. Now that is fun (read nearly impossible) trying to adjust that while playing. Fortunately most pickups never need it.

Blowing something up happens to the best. We've all been there

Quote:
Originally Posted by PlasticIsGood View Post

Compared to Philips single beam mechs, Sony and Philips CDM12 machines seem very fidgety, and get mechanically noisy, apparently beyond the range of adjustment. Ringing, over-hard plastic doesn't help. It's a pity Sony doesn't explain the "correct" method of adjustment. Presumably it allows the system poles and zeros to be optimally spread. I find the two nested subsystems for tracking control hard to get my head around.
Generally speaking a "good" pickup is very tolerant of mis alignment. If the adjustments seem super critical to get it to play and track then usually there is some underlying issue. The proper alignment of tracking and focus servos is complex because they are both an electrical servo loop with a mechanical component in the mix as well. And each interacts with the other. I remember a 3 day Sony course where we pulled all the theory to pieces looking at bode plots of how it all interacts. And after that told "you don't need know all that stuff though to fix them". Great


Quote:
Originally Posted by PlasticIsGood View Post
Mooly, what's a "front end problem", and what points to that? Can it intervene in such a way as to generate a mute signal that goes to the digital output?
I was thinking before the analogue stages, quite how far before is hard to say though.
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Old 8th January 2013, 02:46 PM   #60
nuryev is offline nuryev  Australia
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Hi all, back to the CD63ki. I was waiting for the laser replacement and installed it today.

The cdp spun up immediately and played better than ever. However, the audio dropped out after about 2mins and 90 seconds of play. I removed the board and checked most joints and resoldered anything that looked suspect including the regulator legs. I may have to now put the project on 'indefinite hold' until I get a scope and learn how to use it effectively.
Thanks for all your patience and suggestions. If anyone has had the same problem and can suggest a fix it would be appreciated.
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