October 13th, 2005
OK, here's another installment of "The PC Doctor takes stuff apart so you don't have to!" This time I'm taking apart an old (and dead) [tag]CD-RW[/tag] drive.
This entry is going to be image intensive so I will post thumbnails - click on these you'll get a bigger image.
OK, so here’s the drive I’m taking apart – an old TDK [tag]CD burner[/tag] that just mysteriously died on me. Next to it is the only tool I’ll be using – a Leatherman Ti Charge.
First, find the screws to get the case off. This drive was held together by four.
After undoing the screws it’s a case of lifting off the metal plate to uncover the internals of the drive.
The front fascia of the drive is held in place by small plastic clips that need to be depressed to release them. I had to depress then a little way now to free the circuit board.
The circuit board is also held in place by small clips that need pressing out of the way to release it. This can be quite a task as there are a number of clips and each seem to pop back into the locked position as soon as you let go of it.
It’s now also time to undo the ribbon cables. To do this all you need to do is pull back on the locking mechanism on the connector and the ribbon comes out – a very neat idea indeed!
Here’s a closeup of the removed ribbon and the connector.
Here is the circuit board separated from the rest of the drive.
This little switch on the circuit board is used by the drive to detect when the tray is open. It is moved from side to side by the tray release mechanism. Pretty clever really!
This is a closeup of the drive tray release mechanism. This is motor controlled usually but this is also the bit that you push against with a paperclip to release the drive tray in an emergency.
The front of most drive trays separate from the trays easily so you can remove the fascia (although some are glued on permanently).
Now it’s time to release the fascia and remove it from the drive.
Now I can remove the internals of the drive from the metal outer case and see the insides of the drive. At the bottom-left of the picture you can see the motor that moves the read/write laser head and in the top-right of the picture you can see the tray motor mechanisms.
Now to undo the spindle cover so I can get at the laser assembly. Most of the internal screws in the drive are tough to remove because they are locked in place using a thread adhesive.
Here’s out first closeup of the laser assembly that runs along a greased rail and the spindle that grips and turns the CD. In the top-right of the picture is the tray motor assembly.
Here is a closeup of the motor that powers the laser assembly to move it along the spinning disc. Not much to see from the top!
This is a closeup of the tray control mechanism. If you take a close look at the center of the second code from the right you’ll notice that this is held in place by a clip. All the other cogs are held in place by this single cog.
Here is the tray locking mechanism that keeps the tray shut when it’s closed. Notice the load of grease used to keep things moving smoothly. You can also see a screw to the right that has a rubber vibration-dampening washer on it. A lot of attention is given to dampening vibrations in optical drives.
These six screws need removing to free the laser head assembly and see underneath.
Laser assembly removed! The cogs that control the head movement are now easily visible.
This is a clever bit – the main head control motor cog has segments of magnetic material embedded in it that is detected by the reed switch that you can see to the bottom-left of the cog. This is used by the drive to know how many rotations it has made so it can keep track of the position of the laser head relative to the CD.
The cog on the left, also part of the laser head assembly, is very interesting. It features a spring to eliminate backlash so that the system doesn’t jump teeth on the cog and cause problems. The shock is absorbed by the spring you can see at the top.
This is a side-view of the cog assembly.
Here I’ve removed the laser head. This is a view of the underneath of it. The comb on the right is the big that the teeth of the main drive cog connects to in order to move the head assembly. It’s not a solid big of plastic because this way they can press it against the cog and it acts as though it’s spring-loaded.
This is a closeup of the laser lens. Notice that this is on a tiny motor that controls its orientation. This is a magnificent bit of engineering!
Here the cover of the lens assembly is removed so you can get a closer look at the motor that controls it.
This is the rear of the laser/lens assembly.
This is the big that does the reading and the writing – this is the laser module which emits the laser beam that comes out of the lens.
Here again is another shot of the laser, but this one also shows two prisms – a bar of glass that looks pink (this is because it is coated) and below that a more normal looking prism. These prisms take the laser light and pass it to the lens and also takes the laser light reflected back from the disc to the detector, which you can just see here at the top-middle of the image.
Here are the two prisms removed from the assembly. They were held in place by a waxy adhesive.
Here is the laser assembly removed from the drive.
Closeup of the front of the laser assembly. Pretty boring shot!
Another shot of the laser assembly.
Here is the actual laser from the assembly. It’s tiny and I had to be quite brutal with it to get it out!
And finally, there is a closeup of the laser detector. This picks up on the scattering of the laser light when it strikes the disk. This, like the laser, is a tiny bit of kit.
This entry was posted on Thursday, October 13th, 2005 at 15:19 and is filed under Kit!, Random Stuff .... You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.