Hi Salar,
Yes, your OMS-5/7 is a single beam laser on a conventional slide type mechanism. As for the complexity, the addition of the diffraction grating adds that part and it's adjustment. This is normally done at the factory (someone should tell Pioneer that). Many early heads (not Philips types) did have an adjustment for that and it was a frustrating and touchy adjustment. The adjustment is made with an eccentric cam on a hand tool. I have a couple examples. Most heads arrived nicely adjusted, but Yamaha and a couple others did provide access to this adjustment. Pioneer heads were never adjusted properly from the factory and it was necessary to do this alignment ... on a plastic head no less. All the other heads were either die cast and milled, or super cheap (Hitachi HOP-M3 - cheap and really nasty).
The "wheel" contained the objective lens and the two coils for tracking and focus. This could have been a killer good head, except that Sony struck again. The bearing on the "wheel" gets stuck and binds on the central pole (guide). I'm not certain what causes this, but you have to remove that assembly and clean the pole and inside the sleeve bearing on the "wheel". I use a touch of an extremely light oil with the consistency of water. It takes just a tiny, tiny amount. I wonder if the pole is coated with Moly? Maybe you can figure that one out Salar. I think the basic idea for that head is sound.
The positions of all the optical elements is super critical. This includes the mean distance and the orientation in free space. Not surprisingly, you would want the build area to be free from lint, dust and air borne oils and such. The easiest way to set these up may be a set of jigs, then fine adjustment set screws using a "standard" laser, then you can mount the one that goes in there and align it. There will be some materials science involved for the suspension for the lens in the "wheel" or it's equivalent. Any lubricants must be the correct ones for the job (this means you - Sony!)
The picture third down would require me to get a head to be certain about what may or may not be missing. The pickup diodes are normally in a different area of the optical path. The laser would heat up to some extent, but I have never measured the temperature. Things may expand enough to throw out the internal alignment a bit (which is why you align a CD player after it has warmed up. The link you provided looks like a Denon CD player. It's best to avoid worm gears unless you limit the position of the motor shaft. Moving back and forth is hard on the brushes inside the motor.
-Chris
Yes, your OMS-5/7 is a single beam laser on a conventional slide type mechanism. As for the complexity, the addition of the diffraction grating adds that part and it's adjustment. This is normally done at the factory (someone should tell Pioneer that). Many early heads (not Philips types) did have an adjustment for that and it was a frustrating and touchy adjustment. The adjustment is made with an eccentric cam on a hand tool. I have a couple examples. Most heads arrived nicely adjusted, but Yamaha and a couple others did provide access to this adjustment. Pioneer heads were never adjusted properly from the factory and it was necessary to do this alignment ... on a plastic head no less. All the other heads were either die cast and milled, or super cheap (Hitachi HOP-M3 - cheap and really nasty).
The "wheel" contained the objective lens and the two coils for tracking and focus. This could have been a killer good head, except that Sony struck again. The bearing on the "wheel" gets stuck and binds on the central pole (guide). I'm not certain what causes this, but you have to remove that assembly and clean the pole and inside the sleeve bearing on the "wheel". I use a touch of an extremely light oil with the consistency of water. It takes just a tiny, tiny amount. I wonder if the pole is coated with Moly? Maybe you can figure that one out Salar. I think the basic idea for that head is sound.
The positions of all the optical elements is super critical. This includes the mean distance and the orientation in free space. Not surprisingly, you would want the build area to be free from lint, dust and air borne oils and such. The easiest way to set these up may be a set of jigs, then fine adjustment set screws using a "standard" laser, then you can mount the one that goes in there and align it. There will be some materials science involved for the suspension for the lens in the "wheel" or it's equivalent. Any lubricants must be the correct ones for the job (this means you - Sony!)
The picture third down would require me to get a head to be certain about what may or may not be missing. The pickup diodes are normally in a different area of the optical path. The laser would heat up to some extent, but I have never measured the temperature. Things may expand enough to throw out the internal alignment a bit (which is why you align a CD player after it has warmed up. The link you provided looks like a Denon CD player. It's best to avoid worm gears unless you limit the position of the motor shaft. Moving back and forth is hard on the brushes inside the motor.
-Chris
Hi Mark,
And our normal members also are going to see those videos as instructions on what and how to service their own machine.
I am regarded as an engineering technician by some of the (real) design engineers I know. If you are going to design a new product / part, you begin by examining existing technology and the failure points in that design. This is normal R&D practice, and one I follow on large campus phone and paging installations, which includes the wireless extensions. The same thing applies when I integrate existing hardware with the new hardware, or systems using devices from different manufacturers. I also attended Ryerson here in Toronto. They teach University level courses and are well respected. My background includes formal training in the field I am working in. I do habitually use network and spectrum analyzers as well as the signal generators and other very good instruments. It's all HP, Agilent and Tektronix equipment for the most part. I do approach this exercise from an R&D standpoint.
I am very glad that you are picking this stuff up. I do wish to know approximately what you know so that I can address your needs better. I am not trying to prove a point. I began with the assumption that you were properly trained on this subject in order for you to comment from a level of good understanding. This isn't the case.
Ask someone off-line if you wish. Salar knows me well enough to let you know where I am coming from. My position is simple. I want the proper information to get out there. Salar is the designer in this case and I am one of his resources, that's all.
-Chris
Absolutely!!!
And our normal members also are going to see those videos as instructions on what and how to service their own machine.
I am regarded as an engineering technician by some of the (real) design engineers I know. If you are going to design a new product / part, you begin by examining existing technology and the failure points in that design. This is normal R&D practice, and one I follow on large campus phone and paging installations, which includes the wireless extensions. The same thing applies when I integrate existing hardware with the new hardware, or systems using devices from different manufacturers. I also attended Ryerson here in Toronto. They teach University level courses and are well respected. My background includes formal training in the field I am working in. I do habitually use network and spectrum analyzers as well as the signal generators and other very good instruments. It's all HP, Agilent and Tektronix equipment for the most part. I do approach this exercise from an R&D standpoint.
Yes, but don't take instruction from non-professionals, or even people doing silly things because they've "heard that" a procedure is vetted by some professional individual or company.
That is a perfectly valid point which I agree with. However, it is Salar in this case that ought to be disassembling things, not someone in a video.
I'm afraid to ask what your "take away" was from that material. As for learning about this subject, sitting down with the proper instruments, jigs and source materials would teach you a great deal more. Knowledge won from direct experience is the best you can get as long as it is backed up with physics and a knowledgeable mentor. Someone who was trained in a professional setting. I was lucky enough to have been trained by some engineers (real ones who designed the transports). Application notes (not white papers!!) is another source of excellent information. These documents are written by application engineers and staff scientists.
I am very glad that you are picking this stuff up. I do wish to know approximately what you know so that I can address your needs better. I am not trying to prove a point. I began with the assumption that you were properly trained on this subject in order for you to comment from a level of good understanding. This isn't the case.
Ask someone off-line if you wish. Salar knows me well enough to let you know where I am coming from. My position is simple. I want the proper information to get out there. Salar is the designer in this case and I am one of his resources, that's all.
-Chris
Which system, one beam or three beam is more easy to adjust / setup?
What are the jigs?
Now, you have seen the disassembled KSS-123A.
How is the diffraction grating adjusted? Is it two parts, the frame that carries the spring, seen from the outside.
and another optical element with blue frame, seen from the inside?
Why a spring? The laser casing seemed to sit tight in the cabinet, without any additional adjustment needed.
Any idea, who produced the laser?
All the best, Salar
What are the jigs?
Now, you have seen the disassembled KSS-123A.
How is the diffraction grating adjusted? Is it two parts, the frame that carries the spring, seen from the outside.
and another optical element with blue frame, seen from the inside?
Why a spring? The laser casing seemed to sit tight in the cabinet, without any additional adjustment needed.
Any idea, who produced the laser?
All the best, Salar
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Chris, like you, I am just trying to supply a little information. My experience is in using CD/CD-R/DVD analyzers made by companies like CD-Associates, Datarius and APEX Systems inc. Each of these machines costing $100k or more.
As an example, the APEX machine has a custom build CD-R drive the size of a shoe-box connected to a PC, Spectrum Analyzer, Time Interval Counter and other supporting equipment.
The two main purposes for using this equipment are QC and optimization of the manufacturing process. QC is easy. You test the first disc and if it is bad you stop the press. Optimization needs a lot more knowledge of the CD technology and the production processes. From Polycarbonate to playback and everything in between.
I think you could say that I have a good level of understanding of the technology.
These are the toys I play with and where the analyzers play an important roll:https://www.youtube.com/watch?v=NDHIDhoLtE0
As an example, the APEX machine has a custom build CD-R drive the size of a shoe-box connected to a PC, Spectrum Analyzer, Time Interval Counter and other supporting equipment.
The two main purposes for using this equipment are QC and optimization of the manufacturing process. QC is easy. You test the first disc and if it is bad you stop the press. Optimization needs a lot more knowledge of the CD technology and the production processes. From Polycarbonate to playback and everything in between.
I think you could say that I have a good level of understanding of the technology.
These are the toys I play with and where the analyzers play an important roll:https://www.youtube.com/watch?v=NDHIDhoLtE0
Hi Salar,
The three beam system is the one to go with. A single beam system requires an oscillator to swing the beam back and forth to find and keep on the track on the CD/DVD.
The three beam systems have a main beam in the center, then two minor lobes to each side. The track edges are captured by the E and F diodes in the pickup array, the others being A through D in a square divided into four equal squares. This signal is used for both focus and recovering the information off the media. It is a robust system, and I think all CD players are now 3 beam.
The jigs I am referring to are milled brass or other metal used to position parts with extremely high accuracy into a larger assembly. Jigs can be a variety of shapes and sizes and be designed to position just about anything. They are - were often used for tape transports and can be extremely close tolerance. For your purposes, they would be used to position the parts of a laser head assembly.
The diffraction grating is often positioned with a jig, then fine adjusted. After this the set components (screw or cam) are locked into place and often hidden from the outside as they are now set forever. It's not normally something that needs periodic adjustment. The adjustment is done in the field by monitoring the eye pattern while adjusting the grating position. There will be three points where you can see an eye pattern, you tune to the maximum level for the middle eye pattern. The CD loses lock completely in five areas, so the servo must be in a test mode. After this there is an electrical balance done for the pick up diodes called E-F balance. This is a critical, touchy adjustment. It makes all the difference in the world to performance.
The spring is used to maintain pressure on the components as the temperature changes cause expansion and contraction. Pretty neat eh? The only other reason why they might put a spring in is to surprise the heck out of folks who like to take things apart!
When you are dealing with dimensions on the order of a laser light phase, a grain of dust can create disaster. Everything is done in a clean room or inside a machine that has a clean compartment (like making a CD for example). So there are tiny adjustments that are needed, and lasers are used to indicate where the proper alignment position is.
I don't know who produced the laser. I know Sharp does, probably Toshiba too. I'm sure this is a well served market.
-Chris
The three beam system is the one to go with. A single beam system requires an oscillator to swing the beam back and forth to find and keep on the track on the CD/DVD.
The three beam systems have a main beam in the center, then two minor lobes to each side. The track edges are captured by the E and F diodes in the pickup array, the others being A through D in a square divided into four equal squares. This signal is used for both focus and recovering the information off the media. It is a robust system, and I think all CD players are now 3 beam.
The jigs I am referring to are milled brass or other metal used to position parts with extremely high accuracy into a larger assembly. Jigs can be a variety of shapes and sizes and be designed to position just about anything. They are - were often used for tape transports and can be extremely close tolerance. For your purposes, they would be used to position the parts of a laser head assembly.
The diffraction grating is often positioned with a jig, then fine adjusted. After this the set components (screw or cam) are locked into place and often hidden from the outside as they are now set forever. It's not normally something that needs periodic adjustment. The adjustment is done in the field by monitoring the eye pattern while adjusting the grating position. There will be three points where you can see an eye pattern, you tune to the maximum level for the middle eye pattern. The CD loses lock completely in five areas, so the servo must be in a test mode. After this there is an electrical balance done for the pick up diodes called E-F balance. This is a critical, touchy adjustment. It makes all the difference in the world to performance.
The spring is used to maintain pressure on the components as the temperature changes cause expansion and contraction. Pretty neat eh? The only other reason why they might put a spring in is to surprise the heck out of folks who like to take things apart!
When you are dealing with dimensions on the order of a laser light phase, a grain of dust can create disaster. Everything is done in a clean room or inside a machine that has a clean compartment (like making a CD for example). So there are tiny adjustments that are needed, and lasers are used to indicate where the proper alignment position is.
I don't know who produced the laser. I know Sharp does, probably Toshiba too. I'm sure this is a well served market.
-Chris
Here is a German supplier of lasers and optics. They may also be able to help with the design or even do simulations.
Laser Diodes - Laser Components GmbH
Laser Diodes - Laser Components GmbH
Hi Mark,
You don't seem to completely understand how a CD player works after your product has been made. I think what is happening here is that in your plant, someone has come up with some quick metrics that are supposed to indicate if a disc would fail to read properly. The main assumption is that an error rate below a certain minimum indicates a good disc. This isn't always true of course. To assess the quality of a CD requires training some human machines - not very cost effective. However, poor eye patterns and translucent discs are a fact and these things are poor quality. You have to understand that the business of making DVDs or CDs tends to save money in every place it can be done without (not dropping quality) complaints from customers. As long as a CD doesn't skip or not read, they have no idea when the audio quality suffers.
Every test CD is opaque with high reflectivity and very good pit shape. What is being produced as normal fodder is nothing close to what the standard says. If you were to assess the quality of the eye pattern you would see what I mean, but you don't. You rely on error rate numbers generated by a highly tuned sample machine (would we love to be able to buy those!). You can feel good about your job and the product you produce and there is no truth to be leaked. Perfect business model.
I have seen a real CD plant in operation where they stamp the Poly-carbonate, then silver it. Back then they created a good product and most of the beam went where it was supposed to go. Today's CD manufacture is more efficient and probably has a lower failure rate. They have become very good at producing a mediocre product where quality sails a little above the defective line. It's never a good product compared to what it could be - or what it was. It has been carefully engineered to be so-so okay, not good.
I know more than I want to about CDs and DVDs. My view is at the interface between your product and the various machines out on the market designed to play them. The eye pattern is more sensitive to conditions than an error rate number is. You know far more about how to create that product, but you seem to be unaware of what happens during the playback process and how disc defects impact playback. If you were told to optimize a certain factor, you could do that competently I'm sure.
Mark, if you do get a chance, take some CDs into your service area and have a gander at the various eye patterns. Try some different machines, some older ones as well. Play with things like focus offset and tracking offset. Then play with some gains. If you have a good technician there with you, have him show you E-F balance and have him identify the various disc defects and the resulting eye pattern. I promise you that the level of your understanding will have increased to a point where you might even get a feel for CD players in distress and the distortion it can create.
Too bad you couldn't see the eye pattern from a Nakamichi OMS-5 or 7 with a good disc. This is as good as things get, because a playing CD looks like a picture of the perfect eye pattern in a book. This is while it is playing. Throw some of your new ones in for sh*ts and giggles. This is one of those things that you will understand once you see things for yourself. Then you will know that BLER rate is only a poor approximation for what is really happening.
This is all said with sincere hopes that you can experience things "where the rubber meets the road". (I hate clichés) I think the experience would teach you a lot.
Best, Chris
You don't seem to completely understand how a CD player works after your product has been made. I think what is happening here is that in your plant, someone has come up with some quick metrics that are supposed to indicate if a disc would fail to read properly. The main assumption is that an error rate below a certain minimum indicates a good disc. This isn't always true of course. To assess the quality of a CD requires training some human machines - not very cost effective. However, poor eye patterns and translucent discs are a fact and these things are poor quality. You have to understand that the business of making DVDs or CDs tends to save money in every place it can be done without (not dropping quality) complaints from customers. As long as a CD doesn't skip or not read, they have no idea when the audio quality suffers.
Every test CD is opaque with high reflectivity and very good pit shape. What is being produced as normal fodder is nothing close to what the standard says. If you were to assess the quality of the eye pattern you would see what I mean, but you don't. You rely on error rate numbers generated by a highly tuned sample machine (would we love to be able to buy those!). You can feel good about your job and the product you produce and there is no truth to be leaked. Perfect business model.
I have seen a real CD plant in operation where they stamp the Poly-carbonate, then silver it. Back then they created a good product and most of the beam went where it was supposed to go. Today's CD manufacture is more efficient and probably has a lower failure rate. They have become very good at producing a mediocre product where quality sails a little above the defective line. It's never a good product compared to what it could be - or what it was. It has been carefully engineered to be so-so okay, not good.
I know more than I want to about CDs and DVDs. My view is at the interface between your product and the various machines out on the market designed to play them. The eye pattern is more sensitive to conditions than an error rate number is. You know far more about how to create that product, but you seem to be unaware of what happens during the playback process and how disc defects impact playback. If you were told to optimize a certain factor, you could do that competently I'm sure.
Mark, if you do get a chance, take some CDs into your service area and have a gander at the various eye patterns. Try some different machines, some older ones as well. Play with things like focus offset and tracking offset. Then play with some gains. If you have a good technician there with you, have him show you E-F balance and have him identify the various disc defects and the resulting eye pattern. I promise you that the level of your understanding will have increased to a point where you might even get a feel for CD players in distress and the distortion it can create.
Too bad you couldn't see the eye pattern from a Nakamichi OMS-5 or 7 with a good disc. This is as good as things get, because a playing CD looks like a picture of the perfect eye pattern in a book. This is while it is playing. Throw some of your new ones in for sh*ts and giggles. This is one of those things that you will understand once you see things for yourself. Then you will know that BLER rate is only a poor approximation for what is really happening.
This is all said with sincere hopes that you can experience things "where the rubber meets the road". (I hate clichés) I think the experience would teach you a lot.
Best, Chris
Hi Chris!
As far as I see, not for the wavelength of 785 nm
So you think we should not bother with the one-beamers in the Nakamichi OMS-7 and Toshiba XR-Z70 (OPH-32).
BTW, the lasers look like twins:
http://vintage-audio-laser.com/A-l-atelier-page-65
Great servo control!
And at the bottom of this page about the Nak OMS-7 and Kyocera DA-910:
Clean Eyepattern!
http://vintage-audio-laser.com/A-l-atelier-page-58
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This has APC:
Roithner Lasertechnik - Dot Laser Modules, 780 nm
Mean time to failure (MTTF) >10,000 hours - 13 Months permanent use
No APC and maybe a printing error, lasers from Sheaumann:
http://media.wix.com/ugd/53cbac_6cfba1f0b2264199a13ddbc053378cb4.pdf
Lifetime of 100,000 hours - NINE years?
Roithner Lasertechnik - Dot Laser Modules, 780 nm
Mean time to failure (MTTF) >10,000 hours - 13 Months permanent use
No APC and maybe a printing error, lasers from Sheaumann:
http://media.wix.com/ugd/53cbac_6cfba1f0b2264199a13ddbc053378cb4.pdf
Lifetime of 100,000 hours - NINE years?
Hi Salar,
I can see a nine year life being possible these days. Don't forget how far we have come with LEDs. This is what Sheaumann is basically saying. I think the 80 mW model is what is in current use. Now, if this is in fact a Sanyo replacement, then copying the SF-90 head would be a good idea. It was cheap and cheerful, plus didn't have the distortion the Sony heads and chip sets do. The only problem with the SF-90 head was the crappy bearing for the rod (it didn't have one!!). I believe if you put an SF-90 in a carrier similar to the Nakamichi OMS-7, you would have as close to a perfect eye pattern and long life as you are going to get.
That eye pattern isn't as good as what is normal for the Nakamichi. In fact, that eye pattern isn't about single or three beam laser at all. It's about the laser head assy being aligned mechanically and electrically. I could probably get a great eye pattern from a Sony KSS-210A if it were in a carrier like the Nakamichi unit. The great servo in the Nak doesn't hurt either. The OMS-7II was a bitter disappointment compared to what I was use to. Previously the KSS-123A was used in the OMS-3/4 machines, and they had a better eye pattern than the OMS-7 II. The transport in the OMS-7 II was springy as heck and that sure didn't help the tracking.
I have an OMS-4 as well. I'll bring that out and play with it some more. That one had a stuck laser, that center post problem. I took it apart and repaired it. It would be interesting to see if it still works.
Salar, my vote would be to an SF-90 clone with a good carrier. You might even be able to buy SF-90's and mount them on that universal carrier we talked about earlier.
-Chris
I can see a nine year life being possible these days. Don't forget how far we have come with LEDs. This is what Sheaumann is basically saying. I think the 80 mW model is what is in current use. Now, if this is in fact a Sanyo replacement, then copying the SF-90 head would be a good idea. It was cheap and cheerful, plus didn't have the distortion the Sony heads and chip sets do. The only problem with the SF-90 head was the crappy bearing for the rod (it didn't have one!!). I believe if you put an SF-90 in a carrier similar to the Nakamichi OMS-7, you would have as close to a perfect eye pattern and long life as you are going to get.
That eye pattern isn't as good as what is normal for the Nakamichi. In fact, that eye pattern isn't about single or three beam laser at all. It's about the laser head assy being aligned mechanically and electrically. I could probably get a great eye pattern from a Sony KSS-210A if it were in a carrier like the Nakamichi unit. The great servo in the Nak doesn't hurt either. The OMS-7II was a bitter disappointment compared to what I was use to. Previously the KSS-123A was used in the OMS-3/4 machines, and they had a better eye pattern than the OMS-7 II. The transport in the OMS-7 II was springy as heck and that sure didn't help the tracking.
I have an OMS-4 as well. I'll bring that out and play with it some more. That one had a stuck laser, that center post problem. I took it apart and repaired it. It would be interesting to see if it still works.
Salar, my vote would be to an SF-90 clone with a good carrier. You might even be able to buy SF-90's and mount them on that universal carrier we talked about earlier.
-Chris
Your right about that. One is called Sony, the other Philips. They wrote the RED BOOK (audio) and the YELLOW BOOK (rom).
We use the eye-pattern or really several measurements of the eye pattern.
Jitter, Itop, I3, I11 and asym as specified in the system descriptions. Can you see by looking at the eye-pattern if the T3 pits or the T5 lands are within spec? We take this to a much higher level than just looking at eye-patterns.
If you can extract this data from the eye-pattern that would be great.
Found this thread about the SF-90 in a German forum. What coincidence, seems only to be 2 weeks old:
https://translate.google.com/transl...i-cec-einstein-yba-und-audiomecca/&edit-text=
Used google translate for this.
So both heads could be sticky - what makes the SF-90 better...?
Servo circuitry has to be redesigned anyway, a KSS-123A clone could be made
adjustable in a carrier...?
https://translate.google.com/transl...i-cec-einstein-yba-und-audiomecca/&edit-text=
Used google translate for this.
So both heads could be sticky - what makes the SF-90 better...?
Servo circuitry has to be redesigned anyway, a KSS-123A clone could be made
adjustable in a carrier...?
BTW what is the use of the diodes´angled window in the KSS-123A?
The beam still leaves the can long the middle axis towards the cylindrical lens
like in a "flat" window, doesn´t it?
Is this the reason:
https://en.wikipedia.org/wiki/Brewster's_angle
Doesn´t this mean, that flat windows might have angled lasers - and that a can with an angled widow can be replaced with a flat one?
Interesting...
The beam still leaves the can long the middle axis towards the cylindrical lens
like in a "flat" window, doesn´t it?
Is this the reason:
https://en.wikipedia.org/wiki/Brewster's_angle
Doesn´t this mean, that flat windows might have angled lasers - and that a can with an angled widow can be replaced with a flat one?
Interesting...
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Hi Mark,
Okay, you are monitoring the eye pattern. Fantastic!
Well, to determine Jitter and asym isn't that difficult. You could easily set up a mask for the oscilloscope, almost any Keysight equipment could be used. As the price goes up these better instruments can give you direct jitter values without you having to calculate it. Can you please define these acronyms for me? They are Itop, I3 and I11. The reference "I" makes me think you are looking for values of current in the laser pickup at two locations in the eye pattern. I am doubtful of this being your intent.
-Best, Chris
Do you have to consider the T3 pits or the T5 lands separately? You can easily see the decision points on a good eye pattern. If the pattern becomes stressed and/or noisy you have other problems that are more severe. The eye pattern would need to have processing done to pick out these values in a weedy pattern. But all of your lands and edges are important and it is doubtful the T3 pits or T5 lands will be in specification if the rest of the pattern has gone so far south.
Many of the measurements can be automated with some masks and scripts. You can test a disc in the beginning, and and middle. I'll bet that if you monitor the focus and tracking servos, you could easily and directly get values for eccentricity and warp as well. Those are good indicators if your process becomes a bit uncontrolled somewhere.
Okay, you are monitoring the eye pattern. Fantastic!
Well, to determine Jitter and asym isn't that difficult. You could easily set up a mask for the oscilloscope, almost any Keysight equipment could be used. As the price goes up these better instruments can give you direct jitter values without you having to calculate it. Can you please define these acronyms for me? They are Itop, I3 and I11. The reference "I" makes me think you are looking for values of current in the laser pickup at two locations in the eye pattern. I am doubtful of this being your intent.
-Best, Chris
Do you have to consider the T3 pits or the T5 lands separately? You can easily see the decision points on a good eye pattern. If the pattern becomes stressed and/or noisy you have other problems that are more severe. The eye pattern would need to have processing done to pick out these values in a weedy pattern. But all of your lands and edges are important and it is doubtful the T3 pits or T5 lands will be in specification if the rest of the pattern has gone so far south.
Many of the measurements can be automated with some masks and scripts. You can test a disc in the beginning, and and middle. I'll bet that if you monitor the focus and tracking servos, you could easily and directly get values for eccentricity and warp as well. Those are good indicators if your process becomes a bit uncontrolled somewhere.
Hi Salar,
I guess the SF-91 is the improved replacement. In that case use the SF-91.
The most serious problem with the cheaper heads is related to not using sleeve bearings for the rod(s) where they slide back and forth. Once the wear gets to a certain point, the head begins to crab as it travels and becomes stuck until enough pressure has built up to snap it free. Once that happens the head travels too far forward. Eventually the drive gears will be sheared off somewhere, probably near the head. A small motor can create a lot of pressure due to the reduction ratio normal in the sled motor assemblies. This also sends the tracking motion of the lens to it's maximum forward location. This can cause the servo to overdrive the coil so that it melts the lens housing and outer cover. It will for sure damage the insulation in the coil itself. Not pretty.
Why use the SF family? Cost and ease of dealing with the parent company. I'm not sure about Sanyo, but Sony is both more expensive and a real PITA to deal with.
I may be wrong, but buying an existing product where the tooling already exists will be a lot less expensive than attempting to build from scratch. Just avoid using the guides for anything other than an attachment point to an improved sled. If you can align the head in free space and provide a better sled movement mechanism, you will have achieved the most important step in obtaining a very low error rate compared to other current (and maybe past) CD / DVD players.
It always seemed (to me) that it was such a pity that good optics in the SF-90 were burdened with a poor quality rail interface. The guides wore out long before the head went bad and they were capable of a great eye pattern. Anyone who knows me personally is well aware that I disliked Sanyo products. I liked the Sony product because they were delivering an okay eye pattern, but they lasted longer due to the fact that they really used sleeve bearings. They were also smart enough to use only one guide and a flat surface to drag the opposite head support on. A two post transverse mechanism will be far more picky about alignment if sleeve bearings are used on both sides. The three point guide is far more forgiving of wear.
-Chris
I guess the SF-91 is the improved replacement. In that case use the SF-91.
The most serious problem with the cheaper heads is related to not using sleeve bearings for the rod(s) where they slide back and forth. Once the wear gets to a certain point, the head begins to crab as it travels and becomes stuck until enough pressure has built up to snap it free. Once that happens the head travels too far forward. Eventually the drive gears will be sheared off somewhere, probably near the head. A small motor can create a lot of pressure due to the reduction ratio normal in the sled motor assemblies. This also sends the tracking motion of the lens to it's maximum forward location. This can cause the servo to overdrive the coil so that it melts the lens housing and outer cover. It will for sure damage the insulation in the coil itself. Not pretty.
I didn't know about the SF-90 getting sticky, the guides always wore out first. Maybe its because over time in storage the oil is attacked by microbes so that now there is a problem. They seemed to have solved the problem with the SF-91 - so use that one.
Why use the SF family? Cost and ease of dealing with the parent company. I'm not sure about Sanyo, but Sony is both more expensive and a real PITA to deal with.
I may be wrong, but buying an existing product where the tooling already exists will be a lot less expensive than attempting to build from scratch. Just avoid using the guides for anything other than an attachment point to an improved sled. If you can align the head in free space and provide a better sled movement mechanism, you will have achieved the most important step in obtaining a very low error rate compared to other current (and maybe past) CD / DVD players.
It always seemed (to me) that it was such a pity that good optics in the SF-90 were burdened with a poor quality rail interface. The guides wore out long before the head went bad and they were capable of a great eye pattern. Anyone who knows me personally is well aware that I disliked Sanyo products. I liked the Sony product because they were delivering an okay eye pattern, but they lasted longer due to the fact that they really used sleeve bearings. They were also smart enough to use only one guide and a flat surface to drag the opposite head support on. A two post transverse mechanism will be far more picky about alignment if sleeve bearings are used on both sides. The three point guide is far more forgiving of wear.
Sure it can, except that the head itself is more expensive. You will be paying more for a head that doesn't buy you anything above the SF-91 (say).
-Chris
Hi Salar,
The head should avoid as many turns as possible due to the losses that accumulate with each added element.
Now, here is a thought. It may be less expensive to purchase entire (cheap) machines that have a collection of servos and even the MPU to run the transport. At this point you could retain the mechanism control MPU and modify the servo control for the sled's changed dynamics. The focus and tracking servos wouldn't need any adjustment at all. You can introduce the PIC controller to handle things the way you would like to handle them. An improved disc motor would require a retuned servo.
Thoughts? Mark, thoughts?
-Chris
Think Prism. This could be to sample the beam strength via the monitor diode. I am not at all certain of this. We were taught the basics of head construction ... so many years ago now. My notes (somewhere if not in the garbage) might have defined each element in detail.
Correct for this optical layout.
The head should avoid as many turns as possible due to the losses that accumulate with each added element.
This is where the new sled assembly might become the major cost. The completed SF-91 heads are priced as a commodity. They would be a good value for a complete assembly.
Now, here is a thought. It may be less expensive to purchase entire (cheap) machines that have a collection of servos and even the MPU to run the transport. At this point you could retain the mechanism control MPU and modify the servo control for the sled's changed dynamics. The focus and tracking servos wouldn't need any adjustment at all. You can introduce the PIC controller to handle things the way you would like to handle them. An improved disc motor would require a retuned servo.
Thoughts? Mark, thoughts?
-Chris