CD and DVD players

From Restarters Wiki

This page covers CD, DVD and Blu-ray players.

Summary

An optical disk (CD, DVD or blu-ray, and all the variants) contains a spiral track of minute pits, or spots of different reflectivity. Unlike a vinyl LP, the track starts in the middle and works outwards. In the case of a normal CD, the spiral if unwound would be 5.7km in length. The spots are only of the order of 1/1000mm wide, and the laser has to follow them precisely. In a DVD or blu-ray disk the spots are even smaller and the spiral is considerably longer. It's hardly surprising therefore that players not infrequently fail.

Safety

Warning03.png
Operating mains powered equipment with the covers off may be highly dangerous. You should not attempt it unless you are completely competent to understand and manage the risks, both to yourself and any bystanders.
Lasers in CD, DVD and blu-ray player are not normally powerful enough to present a danger, and in any case, the lens focusses the energy in a spot very close to the lens itself so it should be well scattered before it reaches your eye. Nevertheless, lasers should always be treated with caution. Examining the lens at close quarters or with a magnifying glass whilst the laser is on would be unwise and could be dangerous.

Diagnosis

A laser head from a CD/DVD drive. Two laser power adjustment controls are shown ringed in red.

Problems with the disk tray failing to eject or refusing to load are common, normally due to a mechanical problem.

A visual inspection should first be undertaken. Look for dust, hairs or fluff on the lens, but never touch it with your fingers. Normal house dust is not usually a problem unless the lid has been habitually left open.

The lens is typically suspended on four thin springy wires, allowing it to be moved up and down to focus or sideways to follow the track. Several coils attached to the lens cause it to move relative to fixed permanent magnets when a current is passed through them.

Using a small screwdriver or similar tool, very gently prod the lens to see if it moves freely and springs back to its rest position, but don't move it more than a fraction of a millimetre. Check for any signs that any of the springy wires are broken or distorted. In such a case, a repair is unfortunately not normally practical.

For a CD player that won't play a CD-RW or a CD-R, try a pre-recorded CD. Not all players can play a CD-RW, and it may be that some brands are more challenging to play than others.

For a CD/DVD or DVD/blu-ray player, check whether it will play some types of disk but not others. It may contain 2 lasers, one for CDs and another for DVDs. If it plays one type of disk but not the other then one of the lasers may have failed.

On players where you manually place the disk on the spindle and then close the lid there is usually an interlock which prevents the disk from spinning while the lid is open. You may be able to override this by pressing a lever or micro-switch with a suitable tool. You may need to partially disassemble the unit to do so.

The following should not be tried on mains powered equipment with the covers off unless you are completely sure you can do so safely. If you can override the interlock whilst turning the player on with no disk inserted, you should see the spindle start to rotate, then the lens move to a position close to the spindle. You may then see the laser come on and the lens jiggle up and down as it tries to focus on the disk. CD-only players may use an infrared laser which you won't be able to see come on, though a digital camera or camera phone may. The light from the red laser in a DVD player can be seen as a tiny red spec in the lens.

Repair

If the disk refuses to eject, check for a small hole in the front bezel. Straighten out a paper clip and push it gently but firmly into the hole to forcibly eject. This may not work in the case of a mechanical fault. Combining this with pressing the eject button may help. Also, if possible try ejecting with the unit stood on its end or upside down.

In the case of a CD or DVD drive with a disk tray, this can jam as a result of wear. It will help considerably if you can remove the drive from the equipment in order to examine the mechanism closely. The mechanism comprises an eject motor, a series of cog wheels and a rack and pinion to drive the tray in and out, and a mechanism that clamps the disk to the spindle when fully inserted, actuated by a peg sliding in a groove in the underside of the tray. There is often another peg attached to the latter which locates in a hole in the tray to prevent it moving while the disk is clamped. Through wear, sometimes the peg isn't fully retracted before the tray starts to eject, jamming both the tray and the peg. Using a craft knife or a needle file, sometimes taking a tiny shaving off the peg or slightly enlarging the hole it locates in can cure the problem.

In order to do so you may have to remove the tray. There is normally a catch that stops the tray moving further out than its fully extended position, though you may have to examine it very carefully to spot it and to see how to release it. On reinserting the tray you need to ensure the other parts of the mechanism are positioned correctly, by manually rotating one of the cogs driven by the eject motor. You may have to do this by trial and error.

Dust can be removed from the lens by gently blowing or very gently brushing with a camel hair brush (the sort photographers use for dusting camera lenses). Bits of fluff or hair may only be visible with a magnifying lens. If they won't blow or brush away, try removing very carefully with a fine pair of tweezers and a steady hand. If you use an air duster, don't use it closer than a couple of inches as the violent blast of air may damage the lens suspension.

Check all electrical connections. It may be worth reseating ribbon cables in their sockets as this is easy to do, though they rarely cause problems.

If everything looks good both mechanically and electrically but the player simply refuses to recognise disks or some types of disk, it may be worth adjusting the laser power. If you can gain access to the laser head, look for the laser power adjustment control. In the case of a CD/DVD or a CD/DVD/blu-ray player there may be two separate lasers, each with its own control. Unfortunately there is no simple way to tell which is which.

Adjusting the laser power should be regarded as a last resort. If you turn it up too far you may burn out the laser or damage recordable or re-recordable disks. If the laser is getting weak you may only hasten its deterioration. Mark the original position of the control in some way so you can restore it to its original setting, then move it clockwise by just a very small amount. Then see if the player now recognises disks.

Unlike computer CD/DVD drives, the mechanisms in domestic players are not standardised. Nevertheless, if you have another player with a different fault but a mechanism with the same mechanical fitting and electrical connections, you may be able to swap them over. Even if the players are different brands they could still have compatible mechanisms.