Hi guys,
I have a strange problem with my CD player. It reads computer-recorded CD-R discs without problem, but does not see matrix discs. The player is Сyrus with a Philips CDM-12 mechanism.
What is the difference in the reflective surface of the two types of discs?
I have a strange problem with my CD player. It reads computer-recorded CD-R discs without problem, but does not see matrix discs. The player is Сyrus with a Philips CDM-12 mechanism.
What is the difference in the reflective surface of the two types of discs?
What is a matrix disc?
About 90% of CD problems is a dirty lens that accumulates a greasy dust coating and can blur the image of the pits/lands. This makes reading the CD hit and miss- some CD's will read, some won't. I'm guessing that is the only difference- the visibility of the data, not what it contains.
Have you opened it up and cleaned the lens with a new Q-tip and alcohol? That is step one, then go from there. If you have trouble getting to the lens post some pictures and we can be helpful.
About 90% of CD problems is a dirty lens that accumulates a greasy dust coating and can blur the image of the pits/lands. This makes reading the CD hit and miss- some CD's will read, some won't. I'm guessing that is the only difference- the visibility of the data, not what it contains.
Have you opened it up and cleaned the lens with a new Q-tip and alcohol? That is step one, then go from there. If you have trouble getting to the lens post some pictures and we can be helpful.
Matrix discs are all music discs that we buy from music stores.
The lens is cleaned.
In general, players have a harder time reading CD-R discs, but in my case it's the other way around.
There must be something different about these disc types because this regularity is permanent - CD-Rs are read without problem, but the CDs spins three times briefly and says "no disc".
The lens is cleaned.
In general, players have a harder time reading CD-R discs, but in my case it's the other way around.
There must be something different about these disc types because this regularity is permanent - CD-Rs are read without problem, but the CDs spins three times briefly and says "no disc".
I can only work with the information that you give me.
When the tray is inserted, the laser is usually turned on, and the lens focused in and out to see if a reflection is received indicating a disc is present. If so, then it tries to spin up the disc to read the table of contents (TOC). This is happening on both formats. There are certainly differences in the formatting of the TOC for CD-R than music CD's, but unless you have been hacking/modifying the ROM of your CD player, I stick by my assertion that this is not related to content but a marginality in reading pits and lands/ which are remarkably different in appearance in a laser burned disc than a molded/manufactured disc, and am proceeding with that assumption.
I have seen CD players fail to read the table of contents or have reading errors because:
Once you have eliminated all of the dirt/lube/mechanical issues that are possible, you boil the problem down more and more towards the need for an electrical/optical alignment. Early units have the test connections, adjustments, and documentation you need for an advanced oscilloscope user to walk through this process with a test/alignment disk. It's tricky and difficult. Newer units have this alignment more and more automated, and there is less that you can do to correct it. Do all the easy stuff, then do a deep dive into the service literature, to see what can be done from an alignment standpoint. In the end, it might be better to just replace the unit, but most I have had great luck with the easy stuff I have detailed here.
When the tray is inserted, the laser is usually turned on, and the lens focused in and out to see if a reflection is received indicating a disc is present. If so, then it tries to spin up the disc to read the table of contents (TOC). This is happening on both formats. There are certainly differences in the formatting of the TOC for CD-R than music CD's, but unless you have been hacking/modifying the ROM of your CD player, I stick by my assertion that this is not related to content but a marginality in reading pits and lands/ which are remarkably different in appearance in a laser burned disc than a molded/manufactured disc, and am proceeding with that assumption.
I have seen CD players fail to read the table of contents or have reading errors because:
- the lens is dirty from dust (90% likely)
- the laser is weak after many years of use and worn out (not common but model dependent, check other forum complaints)
- the laser/lens mechanism is out of physical or optical alignment (was touched or dropped)
- the sled rails are dirty and/or dragging from dirt accumulation and lube drying out (very common, maintenance item #2 after lens cleaning)
- the laser/lens electrical control system is out of alignment due to mechanical and component aging (more common depending upon age)
- the CD is not sitting flat on the spindle due to schmutz on the spindle traction ring or missing ring. (very typical, maintenance item #3)
- the CD is scraping/dragging on part of the tray assembly due to tray wear or worn out belts (very common some models, often in older units)
- the spindle compression puck is scraping on it's holder because the tray is not actually locking fully closed due to belt wear or slipping.
- the spindle motor is too slow to bring the disc up to speed before it times out (damaged, worn out, or dry lube). I saw this in a big number of CD players from the 90's that had "weak" spindle motors- we changed out dozens, thousands nationally.
Once you have eliminated all of the dirt/lube/mechanical issues that are possible, you boil the problem down more and more towards the need for an electrical/optical alignment. Early units have the test connections, adjustments, and documentation you need for an advanced oscilloscope user to walk through this process with a test/alignment disk. It's tricky and difficult. Newer units have this alignment more and more automated, and there is less that you can do to correct it. Do all the easy stuff, then do a deep dive into the service literature, to see what can be done from an alignment standpoint. In the end, it might be better to just replace the unit, but most I have had great luck with the easy stuff I have detailed here.
CD-R are typically less reflective (about 60 to 70% the value of a commercial disc) and CD-RW a lot lower still. The data coming off the disc is always more jittery and less well defined than a commercial pressed disc. So your problem is a strange one 😉
I would always suggest looking at the RF to see how clean it looks and crucially what the amplitude is like. CDM12's (12.1 and 12.4's are typically around 1.2 to 1.5 volts peak to peak) If the laser power is to high (how could that happen though...) then its remotely possible for CDR's to seem OK while commercial discs fail.
So you need initially to look at the RF and also look at what is present while the pressed disc briefly spins.
Maybe the problem is too much laser power.
CD-R are less reflective than CD originals, with too much laser power, RF is distorted in CD originals. Maybe this can be the explanation.
CD-R are less reflective than CD originals, with too much laser power, RF is distorted in CD originals. Maybe this can be the explanation.
I call RF the signal that laser pickup deliver to the CD Player. Yes, you can see RF signal with a cheap oscilloscope. It's is something like this:
https://www.diyaudio.com/community/attachments/img_6672-jpg.1049010/
First of all, don't touch laser power adjust, just take some pictures of CD and CD-R RF signal and show it to us.
https://www.diyaudio.com/community/attachments/img_6672-jpg.1049010/
First of all, don't touch laser power adjust, just take some pictures of CD and CD-R RF signal and show it to us.
Please correct me if I am wrong: CDRs have a "burnt in" landscape that the laser reads, matrix discs are "stamped": there are high and low areas, with one the laser tends to cancel out, with the other it adds up light. The "burnt" disc contains burnt and not burnt areas: where it's burnt (imagine blackened plastic bubbles or the like) the reflection becomes dim. Sorry for the primitive explanation, hope it helps...
Did you bother to work through the check-list of many much more basic and very common problems first? What did you find? I would strongly suggest not touching ANY trimmer unless you are geared up with the service literature procedures, skill, test disc, interconnects, and adequate sensitivity high speed scope to enact the full alignment, because once you dork with this very sensitive and cranky system you will likely be inducing much more difficult to solve problems. No, lasers to not magically change to suddenly run at too high an output, and no, I would not turn it down, that's not the problem. This is a reading marginality in an older player that just happens to show up more on one format than another because of a myriad of reasons. If the check list does not help, then gear up and do a full alignment from scratch, don't pot-shot and hope to get lucky. There are youtube videos that can be very helpful in understanding what you are getting into.
You need a scope with a decent bandwidth (say 10MHz +) so a cheap handheld type (if that is what you have) probably won't cut it. An very modest analogue (CRT based) scope will outperform even a fairly expensive digital one for this kind of thing. The RF is the combined signal from the photodiode array in the pickup of the encoded data on the disc. To look at it consists of what seem like overlapping sine waves and any music disc always gives the same pattern to look at when playing.
RF looks like this on an analogue scope.
It could be either depending how the circuit is configured. Only way to know is to either use a laser power meter (which I don't like for various reasons) or look at the RF.
A cheap analogue scope will easily cope with this. Different story for cheap digital though.
Essentially yes, that's correct. Pressed (stamped) disc are all reflective (pits and lands) and the 1's register wherever there is a transition from one to the other. These transitions are linked to the clock frequency. To get a sequence of 1's or 0s there must be no change over a period of time that spans one or more clock pulses. The reflected light uses phase cancellation to get a difference in level between the pit and land.
CDR's and RW's use a reflective disc and dye. The dye can be darkened by 'burning' with the laser and that creates a similar effect to the pit and land but now only the land is reflective, the 'pit' (or where the pit would be) is just dark.
I had read somewhere that exactly these waves, as in the picture above, cannot be observed even with an expensive digital scope. Must be analog.
Some time ago I bought an old analog "Philips PM 3226" but it needs service, maybe dirty switches and dry capacitors. So I have to do this first. The one I have is a 20MHz USB type.
Some time ago I bought an old analog "Philips PM 3226" but it needs service, maybe dirty switches and dry capacitors. So I have to do this first. The one I have is a 20MHz USB type.
Try it. The bandwidth is OK but I suspect you will see a lot of quantisation errors on what is a complex waveform.
Put it this way, a 50 year old analogue scope of 10Mhz bandwidth will blow away a typical 100 or 150Mhz digital scope (and lets say digital in the 1 to 2k £$ range for stuff like this).
For sure top of the line digital is good but you are looking at 12 bit scopes with 500Mhz bandwidth to do what a regular cooking grade analogue can show and display when it comes to resolution on something like an eye pattern.
Not these days, as my 200MHz Siglent 'scope will testify, like most new digital 'scopes it has phosphor emulation which does what you want here. And truly expensive digital 'scopes will have eye-diagram visualization modes which blow away anything analog, as you can directly measure eye statistics.
The typical digital scopes we often see folk on the forum using will not show an eye pattern with the resolution and clarity of analogue. For sure 'expensive digital' is a different ball game. Analogue simply shows it as it is, digital tries to show what it thinks it should be by use of complex processing and algorithms. It is a bit like comparing 128kb MP3 with wideband analogue.
As with anything though, price gets you performance.
https://www.diyaudio.com/community/threads/kav-300-cd-spin-but-stops.412507/post-7681209
As with anything though, price gets you performance.
https://www.diyaudio.com/community/threads/kav-300-cd-spin-but-stops.412507/post-7681209
In an era of an increasing anti-science tendency, this kind of comment does no one any favours.
I disagree and its nothing to do with being 'anti science' either. You have to look at the full picture and compare like for like and when it comes to digital costs escalate dramatically to get the performance needed for displaying what are complex waveforms.
The image by jpk73 is a perfect example. It initially looks good... but look closer and it is a poor representation of what it should be. What is all the noise at the top and bottom of the signal. Quantisation noise? or is the player faulty (it's not).
There is just no comparison in resolution. I certainly 'get' the appeal of a digital scope but unless you go really high spec you will not match a basic analogue scope for resolution and resolving power.
Great example of an analog scope showing the RF eye pattern: is that posssible with a vintage 10MHz oscilloscope?
Slightly OT but my Arcam 170 (with CDM-1 MK2 which is a CDM4 with hall motor and cast iron chassis) also was not reading CDRs properly but had no problems with CDs. I found this posting and lowered the bearing cup at the underside of the spindle by 0.2mm: now it reads CDRs fine. Don't know if that's applicable to a CDM12 though...
Slightly OT but my Arcam 170 (with CDM-1 MK2 which is a CDM4 with hall motor and cast iron chassis) also was not reading CDRs properly but had no problems with CDs. I found this posting and lowered the bearing cup at the underside of the spindle by 0.2mm: now it reads CDRs fine. Don't know if that's applicable to a CDM12 though...
The above is factual. Your reference to trying and thinking isn't. It attacks the underlying science.