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 Post subject: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 12 Feb 2019, 17:24 
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Hey everyone I'm hoping to resolve an issue I have with a 702. I recently acquired and then revitalized this player from the dead. Thanks to the great advice found here, a new belt and some grease was all that it needed...

Or so I thought.

My initial testing was with a CLV title (Beavis & Butthead) and everything worked great; no issues. Great picture, sound and disc flip. Great animation and soundtrack BTW.

However, upon further testing with a CAV disc, I discovered that about 1/3 through the A side the digital audio tracks start to go static until the end of the disc where there is almost no sound! Analog tracks seem ok for now but I need to test further.

I tried 2 movies with 3rd side CAV (Mission Impossible and Stargate) both react the same at the same places and don't exhibit this behavior in my 704 so I know it isn't the discs. I understand these have AC-3 and that is not the static I'm discussing. This is on the digital PCM tracks, not the analog tracks where the AC3 is stored..

I'm using the optical output of the 702 as well as the analog phono jacks. When I select the digital audio track via remote I hear the same static out of the optical AND the phono outputs. My AVR locks onto the optical digital PCM signal and sees 44.1k and never drops out or looses sync but the sound is pure static hash at a certain point. Using the analog connection listening to the PCM track I get the same noise. If I switch to analog its fine.

Oh, and by the way, CDs play perfectly from track 1-15 of That Thing You Do soundtrack (on Playtone Records). No static on either connection analog or digital.

This tells me there must be some component level issue or something. Looking at the board labeled "Digital Audio" nothing seems burnt or broken. All connections look good. I've cleaned the lens of the laser pickup, that isn't it. The picture never breaks up so I don't think its the laser dying or a simple twist of the RF Level pot (not even found on this model). The only thing I can think of is maybe the power supply caps which was mentioned in a previous thread.

Any help or advice to push me in the right direction would be so helpful and appreciated. This player is so close to perfect now I just want to get it back to being useful.

Thanks everyone!
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 02:06 
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Take an oscilloscope and verify the RF test point reads 300mV when playing a CD. If that is not an issue the problem could be the focus servo.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 07:02 
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I was waiting for Kurtis to comment just because I was curious if I might be on the right track for this issue. :)

I had my ProScan LD player (seems it gets mentioned a lot in these posts) have a similar issue about 10 years ago of which there was this odd popping or crackling on digital audio as well as picture distortion toward the end of a CAV disc. I made a guess that it was the focus gain and simply turned it up about 1/8 turn and it appeared to fix both issues.

Hope this is the answer to your problem.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 08:03 
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Thanks you two. I will investigate later this week and report back. Learning a lot on this one...
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 17:42 
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Ok, so I cracked it open this morning and took photos before I did anything. Found the RF level VR and turned it up. Its at max now, didn't take much to get it there. Turning it down results in the same type of distortion I was hearing so that is a clue. Turning it to max seems to have helped but not completely resolved. The last chapter begins with the credits and the score which is very obvious if its distorting. Its much better now than before. Previously there was almost no sound at this point. Now its pretty close to perfect but not quite. Still no problem with the image at all. Looks really nice in fact.

I also turned up Focus Gain and Tracking Gain ever so slightly. No change. I'm not cure what CT max is. TE max sounds like a tangential adjustment but not sure. There is also a Focus Sum Level pot.

I was able to put it into test mode and will continue messing around but could not tell what the RF test point was. I see the block where the test pins are on other players but this one doesn't identify the pins. Even if it did, or I assumed they are the same as other players, I couldn't take measurements with a disc spinning since the test points are under the disc tray. I have a scope but again the actual connections are hard to get to with a disc spinning.

So close.....
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 18:09 
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sonicboom wrote:
Ok, so I cracked it open this morning and took photos before I did anything. Found the RF level VR and turned it up. Its at max now, didn't take much to get it there. Turning it down results in the same type of distortion I was hearing so that is a clue. Turning it to max seems to have helped but not completely resolved. The last chapter begins with the credits and the score which is very obvious if its distorting. Its much better now than before. Previously there was almost no sound at this point. Now its pretty close to perfect but not quite. Still no problem with the image at all. Looks really nice in fact.

I also turned up Focus Gain and Tracking Gain ever so slightly. No change. I'm not cure what CT max is. TE max sounds like a tangential adjustment but not sure. There is also a Focus Sum Level pot.

I was able to put it into test mode and will continue messing around but could not tell what the RF test point was. I see the block where the test pins are on other players but this one doesn't identify the pins. Even if it did, or I assumed they are the same as other players, I couldn't take measurements with a disc spinning since the test points are under the disc tray. I have a scope but again the actual connections are hard to get to with a disc spinning.

So close.....

I'll go with "Cross Talk" and "Tracking Error" but unless you can see on a scope adjusting most of these is a blind guessing game that I'm still only beginning to learn even with a scope.
There's no rush - you already have the scope - so take some time to find the service manual (or closest equivalent) it will probably tell you the part number of that connector for the test points and then you can make up some kind of wiring loom for easier connection - the 8" test disc may make life easier, from there you can follow the manual and start to learn meaningfully as you go...
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 20:37 
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So I took out the tray. Manually clamped a CD (CCR Chronicle Vol.1) and observed the RF signal via test pin 3 and the scope and here is what it looks like.

Attachment:
File comment: Playing a CD. Scope connected to test pin 3.
IMG_2183.JPG
IMG_2183.JPG [ 24.65 KiB | Viewed 435 times ]


Referencing the video online about the adjustments this looks ok. Not the clearest though. They mention adjusting the tangential screw located on the laser pickup or slider mech (CLD-S104). I don't see the same type of adjustment for the 702 so I have not made any changes though playing with the RF level pot does affect what I see on the scope but oddly the sound is not affected. I don't have any 8" discs in CAV with digital audio to test only 8" CLV with digital audio or the Pioneer test disc which is analog only. A full size LD won't allow me to keep the probe attached to observe the RF from the CAV side unless there is a trick to that.

Somewhat out of tricks here but willing to keep trying if there is any advice.

Still plays CDs fine all the way through. I hesitate to turn any VR pots since no other issues exist and I don't want to create more.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 21:10 
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Digital Audio on a CD and on a LD are stored completely differently. CD is a direct digital signal, while LD - even for the PCM audio - is still buried in an RF carrier. My thinking is along the Tangential settings. With CLV, the linear speed of the pickup is constant, whereas the linear distance in CAV increases the longer out the play goes. If the tangential controls cannot maintain the track, it will introduce timing errors in the audio. Is there any difference if playing Side B (from the player perspective) versus Side A? I'm also wondering about a possibly bad spindle motor that might not be spinning at exactly 1800 RPM.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 22:07 
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blam1 wrote:
Digital Audio on a CD and on a LD are stored completely differently. CD is a direct digital signal, while LD - even for the PCM audio - is still buried in an RF carrier. My thinking is along the Tangential settings. With CLV, the linear speed of the pickup is constant, whereas the linear distance in CAV increases the longer out the play goes. If the tangential controls cannot maintain the track, it will introduce timing errors in the audio. Is there any difference if playing Side B (from the player perspective) versus Side A? I'm also wondering about a possibly bad spindle motor that might not be spinning at exactly 1800 RPM.


Thanks for your assistance...

I did try to play CAV on the B flip side - same deal. Good notes on the tangential settings though. Not sure how to adjust that on this player. VR610 Tilt Offset seems to have been set at the factory by melting the dial slightly with a soldering iron to lock it in place. VR607 is Tilt Balance and makes no noticeable difference with small moves.

I guess spindle motor could be an issue but it spins up and looks good with everything I throw at it except CAV sides with digital audio....literally perfect except for this.

One thing to mention is that at 18:04 in this video: https://www.youtube.com/watch?v=FIMBrbRPRro&t=1021s



They describe the Tilt Offset adjustment procedure. In test mode without a disc inserted the Tilt Offset is displayed in the upper left corner. They say adjust VR607 until it reads 7. Since I can't adjust my Tilt Offset (VR610) due to it being melted in place it reads T-D:N. VR607 on this player is Tilt Balance. Adjusting that does not change the T# value. During playback the values do change as expected.

Weird.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 13 Feb 2019, 23:13 
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If the LD is on the harder side for the player to read tangential angle can make a difference. As for the RF level once you get it up to around 300mV you'll start getting a signal with enough amplitude to pull out the digital audio. 300mV would be more than enough. Turning it up higher just adds to the chance to add distortion from having a overdriven signal. You can play the trouble disc and watch the RF level just to see where it is at.
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 14 Feb 2019, 17:04 
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krbahr wrote:
If the LD is on the harder side for the player to read tangential angle can make a difference. As for the RF level once you get it up to around 300mV you'll start getting a signal with enough amplitude to pull out the digital audio. 300mV would be more than enough. Turning it up higher just adds to the chance to add distortion from having a overdriven signal. You can play the trouble disc and watch the RF level just to see where it is at.


So in the photo I posted the scope is set to 20mV/Div and I see the signal is only 2 divisions tall or 40mV correct? This is with the RF Level VR at max. If that is all true then maybe it is the laser/pick up? I can't seem to make the RF signal 300mV on my scope so I'm guessing this is it then?

Turing up the RF level made all the static distortion go away except for very near the end (last 7 minutes?). Perhaps if I could turn it up a bit more I could "pull out" the digital audio from the rest of the signal easier since I'm nowhere near 300mV.

You're saying 300mV is enough but I'm not even 1/2 that so maybe that is the root cause?

Thanks for schooling me on this...
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 Post subject: Re: [CLD-D702] Digital Audio static distortion on CAV sides
PostPosted: 15 Feb 2019, 00:48 
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Is your probe a X10 probe?. Multiply by ten what you read.
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