NAD Laser Assembly

The laser mechanism within the CD transport is a reliable component as lasers go. Lasers are of course mysterious things that most people do not understand; a product of 1980s Star Wars technology, which people think lasts forever. The truth is that laser diodes have a finite lifetime and eventually they die from old age.

Nearly all CD transport mechanisms derive their design from the first mechanism that Philips invented. I always thought that they made a mistake in not standardising the parts, because within a few years, variations of the mechanism produced in the Far East started appearing. Since each mechanism was slightly different, the user had to pay large sums of money for the replacement, or have his lovely CD player thrown in landfill. Of course, everyone chose the cheapest route, which was to buy the latest player, which had more functions.

Laser diodes fail in an interesting way that frustrates the owner of the CD player profoundly. It fails intermittently, in that one-minute it will work and the next they it will not. The owner often blames the CD when he is unaware that the laser is about to go. The first signs are tracks skipping, however that is also associated with a worn out motor that cannot maintain the rpm. Another sign is a crackly and fuzzy sound, which occurs when the laser quality is poor -- due to a weak beam -- and about to fail. The user might also see the classic intermittent "NO DISC" error message. At first, it appears randomly when discs are changed, and then eventually, it will not detect any disc. The system uses the laser to detect the disc, so if the laser is not functioning, then the system simply tells you that there is no disc in the tray!

This unit has a semiconductor laser with a wavelength of 650 nm. Lasers are dangerous, and one must never look directly into the lens assembly. It can cause serious damage, so do NOT mess around with CD players if you are not a qualified and experienced engineer.

This Article Continues...