Monday, 26 April 2010

Why won't my player read a recorded disc?

Failure to read recorded discs in standard CD and DVD players.

This is a subject raised by my good friend Keith V. I wish he hadn’t! However, I’ve ended up with quite a bank of information which I thought might make good subject material for a blog posting. I know he’s going to read this because I haven’t copied it to his email address (one way of getting traffic!). So, thanks Keith, I hope some of this answers your question! I haven’t done one for a little while, so here’s a post-and-a-half! -

A word of warning before reading on:- Have you ever noticed the yellow label that is on the back of CD, MD and DVD players (also the older laser disc players)? One is also frequently placed on or near the laser mech itself inside the machine. This is warning of laser emission which may damage your eye sight – never look directly into the laser, you could end up with impaired vision. The laser output is not something you can see, the emission that is doing the work is in the infra-red region of the light spectrum – out of the visible light range of our eyes. A number of customers that have “had a go”, insist that the laser is OK because they can see a red glow within the lens. This red glow is a visible portion of the light generated, it’s not the bit that actually does the work. It is a bi-product. Don’t forget how a disc is “burnt” in a recorder. The phrase may give a clue. In a recording machine the laser is powerful enough to locally heat and permanently change the dye on the reflective surface of the disc. Think safe and don't look directly into an exposed, working laser.

Failure to read recorded discs in standard CD and DVD players.

This is something that I come across frequently!

The first thing to consider is if the machine used to play such discs. If this is the case, chances are that something within the machine has changed. I find that normally the electronics are pretty robust and reliable. The problem is usually down to laser ageing or contamination. I have theorised a number of possible processes that can take place.

Age related

The laser diode itself can go "low emission" – put simply, the torch by which the CD mech is trying to read the data is fading. Lasers are a bit like light bulbs, they start wearing out from the moment you switch them on. Burnt discs are harder to read than standard production discs. One obvious observation is that they are less reflective, they have to be in order that energy from the recording laser can be absorbed by the surface for the process to take place. Because they are harder to read, it follows that they could also be the first to appear problematic when the laser is failing.

Contamination of the laser pick-up (and other parts of the machine, for that matter) can be a problem. This can be in the form of several types:-

• Dust – can be the usual stuff or pet dust
• Talcum powder – typically in the bedroom player
• Pet hair
• Fluids – spilt drinks, flowerpot overfill, pet fluids (typically cat pee!) – these will often render electronics un-repairable anyway!
• Smoke – it’s surprising how the number of problematic CD and DVD players from pubs and clubs has diminished with the smoking ban (same goes for projectors).

These are the killers of lasers. Surface contamination of the lens is not the problem, it’s deeper inside the laser assembly where the contaminants get into the internal optics where the issue becomes non-reversible. Even a service engineer can’t get to these areas to clean up. A single particle of dust in the right place can reduce the light output or deflect the beam as to make the laser useless. Replacement is the only cure.  By the way, I'm not against the use of lens cleaning discs.  So long as they are used regularly they can keep down the level of contaminants on the laer lens itself.  If you wait until there is a problem, usually they don't work.  Thats because the laser needs to read the TOC of the disc, if it's lens is too grubby, it will not register a disc is in the tray and therefore it won't try to play it.

Burnt discs vs. commercial discs

Commercial discs are “stamped” using a master. Obviously "burnt" discs are produced by a method different to that which commercial discs are made. This method, quite obviously, may not be as accurate a recording as a commercially made disc. All players have built in error detection and correction algorithms in the decoding circuitry/software. The data on a disc is encoded and the decoding in the machine are done in such a way that these errors show up. The player will attempt to anticipate what the data should have been and substitute a correction.

Errors can be due to a number of reasons including:-

• A bad "burn" - random failure of disc writing, see below
Writing burn speed too fast  (common – audio CD’s shouldn’t really be burnt faster than 4x)
• A fault with the burning machine including dust/contamination on the laser lens
• Minute air bubbles in the plastic of the disc
• Cheap discs (one thing I’ve heard very frequently is what a fantastic price a person has paid for discs in the supermarket or on the net, then in the next breath how many they are throwing away because their machine didn’t write properly. OK, there’s a pattern here!)
• Low quality media that has a poor “shelf life”
• Cheap recorders that make mistakes
• Scratches on the playing side of the disc
• Sticky labels – the glue can attack the disk surface (the disks own label on is the only protection between the outside world and the reflective surface of the reading side)
• Scratches on the label side of the disc (same as reason above)
• Discs written on by a sharp device such as ball point pen or pencil (same as reason above)

Errors can also happen when using a PC because of the following:-

• Dust getting into your machine when you open the tray - make sure the outside of the burner is clean to avoid this
• For maximum performance use the “Disc-at-once” mode – there is a greater chance of errors occurring if you use “Track-at-once”
• Fast burning speeds often cause lower quality burns
• Don’t run background programs or screen savers – increased processor activity can cause buffer undrruns
Defragging your hard drive before burning a disc will reduce the risk of your machine being erratic during the burn
• Don’t leave sessions open, always finalise your discs
• Make sure that your player can play the formats that your burner can produce
• Make sure that your media can run at the speed that you intend to burn
• Make sure that you burner firmware is updated
• If using DVD+R/+RW media, making sure that the “Booktype” field (bitsetting) is set to DVD-ROM will give a higher compatibility yield

But what if the problem appears to be none of the above?

Now, there are many methods, different software/firmware and design shortcuts that manufacturers use in the production of a machine (recorder or player). Different types of laser also make a difference to the way a machine retrieves the data. Many high street machines are built to a price. This, believe it or not, does affect the quality of the machine and the playback! I have found that, generally, the better the machine (and, therefore, the more expensive it is), the better equipped it is for detecting and correcting these errors. After all, if you spend a lot of your hard earned on a top-of-the-range Hi-Fi system, you'd hope that the music it played would be more lifelike.  The problem arises when a machine starts detecting multiple errors. Obviously, there could also be a problem within the machine – the manufacturer didn’t expect you to be playing a “low quality” disc and didn’t allow for a high degree of correction, or, the correction circuitry is overwhelmed and simply can’t keep up with the detection circuitry. The player could actually be trying to tell you that the disc you are attempting to play is rubbish! (It doesn’t conform to the recognised recording standard, there are a number of these depending on the type of recording and its intended use – red book, orange book, yellow book, etc.) The fact that the “bad” disc plays in a cheap machine may only be down to the fact that the cheap circuitry recognises the data as roughly correct and lets through some of the errors! This all does beg a compatibility issue.

Don’t forget that the media may not be clear of suspicion as well. If you do find a brand and type of media that works with both your burner and your player, stick with it and buy large quantities. Manufacturers do have a tendency to change the quality and their media ID.

Early machines

Don’t forget that the CD player was introduced in 1982, the CD-R wasn’t conceived until 1988 and wasn’t readily available until 1990. It is unlikely that you will get an early player to read a CD-R. CD-RW didn't come onto the market until even later.  The same may be true of DVD recordable discs and early DVD players.

CD players in “Midi”, “Mini” and “Micro” systems

The “Midi” system became popular around the late eighties. The tendency to build-in the CD player caused me to come up with some interesting theory. All was well with the CD as an add-on, optional, box. It usually sat at the bottom of the stack. When it went inboard, things were still fine…. as long as it was at the bottom! When the high street decided that vinyl was dead and the record player was no longer a necessary inclusion in the package, the CD player tended to move to the top of the stack and was most definitely integrated as part of the whole. That’s when the problems began. All of the heavy power consuming, heat producing components tend to be in the bottom of the box – power transformer, power supply PCBs, amplifiers and their heatsinks, etc. Probably the best place to put them. The point here is that, by simple convection, heat rises. There are normally ventilation holes in the back or sides or both, sometimes in the top. Cool air from the room is drawn in to replace the heated air which is rising and (hopefully) escaping from the top. Along with the cool air, is drawn any contaminants which the room’s air may contain. As this air is heated and it rises, so do the contaminants, which are very nicely deposited over the contents of the unit. Especially the CD player which is at the top. The laser is now dirty and cooked! Also it won’t read the data too well. These days, we now have “Mini” and “Micro” system as well, some with DVD decks instead of CD. You know what comes next.

You might say the disc drive in most PC’s is at the top and has a reasonable lifetime…. This is very true, but all the PC drives that I’ve come across are reasonably sealed in their own tin box, which is mounted into the tower. Dust can’t get in apart from through the front opening tray.

Separate Hi-Fi decks usually go on for a fair while without messing about. In fact, as touched on above, smoke can be the real killer here. Unfortunately, smoke particles are tiny and along with any vapours that they contain, they get everywhere. If the player is on 60 a day, you can bet that the laser is well oiled with tar, etc! They don’t read very well with this encumbrance! There are no hardworking, heat producing power supplies or amplifiers inside a stand alone player. Many of them don’t have any ventilation in the casework, it’s not necessary.

Media lifetime – how long will your recordings last?

When CDs were introduced, back in 1982, they were portrayed as being pretty much indestructible and would play in any state. I’ve searched everywhere to include a clip of the Tomorrow's World episode where a demonstration was done by spreading strawberry jam on a CD before trying to play it.  I can remember a man in Laskeys jumping up and down on a CD and a crowd of onlookers falling about as it skipped wonderfully on playback!
Recordable discs give the impression of a similar permanence and manufacturers have claimed a lifespan of anything between 10 and 200 years. However, tests have been carried out, by professional bodies, on discs stored for less than 2 years and found that a number had become unreadable.

This is not to be taken that all discs last for less than 2 years. Many recoded discs have been kept for much longer and have given no trouble. What can be drawn from all of the information contained here is that if you save precious documents, photos, music, video content, etc. on recordable discs:

• Use good, branded media
• Avoid self-adhesive labels
• Use only felt-tipped or “CD” pens for writing on the disc label area
• Store your CDs in protective “jewel” cases in a dark, cool, dry location
• Make multiple copies of important items
• Copy your data to new discs (or new formats as they appear) every 3 to 5 years

My own conclusion about recordings

As a rule of thumb, I have learnt to adopt the attitude that recorded DVDs are only guaranteed to play back on the machine that made the recording! If you do get a result in something else, it’s a bonus! CDs aren’t so bad and usually work fine.

And now, something completely different - "CD Rot", "CD Bronzing", "Disc Rot"

This I've come across (so far) only in commercially recorded CDs.  It does exist, I have several examples.  In the most frustrating varieties, some sort of chemical action within the CD has attacked the reflective layer and "holes" appear in the silvered (or gold) finish.  The areas around this problem are often tainted an orangey colour.  Worse case scenarios end up looking a bit "lace-edged".  Needless to say, playback is impaired.  It seems that once this does show up, it "spreads" through the entire disc rendering it useless.  This has happened to a number of my "limited" or "special" edition discs, which I now don't seem to able to replace.  Here's another example. The only good news is that it doesn't seem to be contagious!

Note to the reader

Some of the information contained here is based wholly on my experiences in testing, fault finding and servicing machines. Some individuals or organisations may not agree with my views! I have also tried to keep this as non-technical as possible, such that the average “man in the street” can understand what is being said.

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