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devices. Considering that their prices have plummeted over the last few years (and still continue to drop, there is little economic sense in attempting a lengthy repair. When a fault occurs in the drive or in its adapter board, your best course is typically to replace the defective drive outright. Symptom 7-1. The drive has trouble accepting or rejecting a CD This problem is typical of motorized CD-ROM drives, where the disc is accepted into a slot or placed in a motorized tray. Before performing any disassembly, check the assembly through the CD slot for any obvious obstructions. If nothing is obvious, expose the assembly and check each linkage and motor drive gear very carefully. Carefully remove or free any obstruction. Be gentle when working around the load/unload assembly. Notice how it is shock mounted in four places. Disconnect the geared dc motor assembly and try moving the load/unload mechanism by hand. If you feel any resistance or obstruction, you should track it down by eye and by feel. Replace any worn or damaged part of the mechanism, or replace the entire load/unload assembly. Also check the geared motor for any damage or obstruction. Broken or slipping gear teeth can interfere with the transfer of force from motor to mechanism. Replace any damaged gears or replace the entire geared assembly. You might also simply replace the
CD-ROM drive mechanism outright. Symptom 7-2. The optical read head does not seek An optical head is used to identify pits and lands along a CD-ROM, and to track the spiral data pattern as the head moves across the disk. The optical head must move very slowly and smoothly to ensure accurate tracking. Head movement is accomplished using a linear stepping motor (or lin- If you like the idea of creating your own bootable CDs, but don’t like the idea of editing hex code manually, try the following utilities on the Companion CD MKBTCD1.ZIP, The companion CD contains a number of CD-ROM testing/caching utilities. Checkout ear actuator) to shift the optical assembly in microscopic increments—head travel appears perfectly smooth to the unaided eye. Check the drive for any damaged parts of obstructions. When the optical head fails to seek, the easiest and fastest fix is simply to replace the CD-
ROM mechanism outright. Symptom 7-3. The disc cannot be read This type of problem might result in a DOS level sector not found or drive not ready error. Before you reach for your tools, however, check the CD itself to ensure that it is the right format, inserted properly, and physically clean. Cleanliness is very important to a CD. Although the laser will often look past any surface defects in a disc, the presence of dust or debris on a disc surface can produce serious tracking (and read) errors. Try a different disc to confirm the problem. If anew or different disc reads properly, the trouble might indeed be in (or on) the original disc itself. Not only the disc must be clean, but the head optics must also be clear. Gently dust or clean the head optics, as suggested by your drive’s particular manufacturer.

If read problems persist, check the physical interface cable between the drive and its adapter board. Be sure that the cable is connected correctly and completely. Many CD drives use SCSI interfaces—if you are using multiple SCSI devices from the same controller card and other SCSI devices are operating properly, the SCSI controller board is probably intact. If other SCSI devices are also malfunctioning, try anew SCSI host controller board. At this point, either the drive’s optical head or electronics are defective. Your best course here is to replace the drive. If problems persist on a drive with a proprietary interface, replace the adapter board. Symptom 7-4. The disc does not turn The disc must turn at a Constant Linear Velocity
(CLV) that is directed and regulated by the spindle. If the disc is not spinning during access, check to be sure that the disc is seated properly, and is not jammed or obstructed. Before beginning a repair, review your drive installation and setup carefully to ensure that the drive is properly configured for operation. If the drive’s BUSY LED comes on when drive access is attempted (you might also see a corresponding DOS error message, the drive spindle system is probably defective. If the computer does not recognize the CD drive (i.e., invalid drive specification, there might be a setup or configuration problem (either the low-level device driver or MSCDEX might not have loaded properly. If your particular drive provides you with instructions for cleaning the optical head aperture, perform that cleaning operation and try the drive again. A fouled optical head can sometimes upset spindle operation. If operation does not improve, replace the CD-ROM drive mechanism. Symptom 7-5. The optical head cannot focus its laser beam As you saw earlier in this chapter, a CD-ROM drive must focus its laser beam to microscopic precision to properly read the pits and lands of a disk. To compensate for the minute fluctuations in disc flatness, the optical head mounts its objective lens into a small focusing mechanism, which is little more than a miniature voice-coil actuator—the lens does not have to move very much at all to maintain precise focus. If focus is out or not well maintained, the laser detector might produce erroneous signals. This might result in DOS drive error messages. If random, but consistent, DOS errors appear, check the disc to be sure that it is optically clean—dust and fingerprints can result in serious access problems. Try another disc. If anew disc continues to perform badly, try cleaning the optical aperture with Symptom 7-3. The disc cannot be read This type of problem might result in a DOS level sector not found or drive not ready error. Before you reach for your tools, however, check the CD itself to ensure that it is the right format, inserted properly, and physically clean. Cleanliness is very important to a CD. Although the laser will often look past any surface defects in a disc, the presence of dust or debris on a disc surface can produce serious tracking (and read) errors. Try a different disc to confirm the problem. If anew or different disc reads properly, the trouble might indeed be in (or on) the original disc itself. Not only the disc must be clean, but the head optics must also be clear. Gently dust or clean the head optics, as suggested by your drive’s particular manufacturer.

If read problems persist, check the physical interface cable between the drive and its adapter board. Be sure that the cable is connected correctly and completely. Many CD drives use SCSI interfaces—if you are using multiple SCSI devices from the same controller card and other SCSI devices are operating properly, the SCSI controller board is probably intact. If other SCSI devices are also malfunctioning, try anew SCSI host controller board. At this point, either the drive’s optical head or electronics are defective. Your best course here is to replace the drive. If problems persist on a drive with a proprietary interface, replace the adapter board. Symptom 7-4. The disc does not turn The disc must turn at a Constant Linear Velocity
(CLV) that is directed and regulated by the spindle. If the disc is not spinning during access, check to be sure that the disc is seated properly, and is not jammed or obstructed. Before beginning a repair, review your drive installation and setup carefully to ensure that the drive is properly configured for operation. If the drive’s BUSY LED comes on when drive access is attempted (you might also see a corresponding DOS error message, the drive spindle system is probably defective. If the computer does not recognize the CD drive
(i.e., invalid drive specification, there might be a setup or configuration problem (either the low-level device driver or MSCDEX might not have loaded properly. If your particular drive provides you with instructions for cleaning the optical head aperture, perform that cleaning operation and try the drive again. A fouled optical head can sometimes upset spindle operation. If operation does not improve, replace the CD-ROM drive mechanism. Symptom 7-29. You cannot change the CD-ROM drive letter under Windows 95 You need to change the drive’s settings under the Device manager:
- Open the Control panel and select the System icon.
- Once the System properties dialog opens, click on the Device manager page.
- Locate the entry for the CD-ROM. Click on the + sign to expand the list of CD-
ROM device.
-
Doubleclick on the desired CD-ROM.
- Once the CD-ROM drive’s Properties dialog appears, choose the Settings page.
- Locate the current drive letter assignment box and enter the new drive designation. Multiple letters are needed only when a SCSI device is implementing LUN addressing (i.e., multidisc changers.
- Click on the OK button to save your changes.
- Click on the OK button to close the Device manager.
- A System settings change window should appear. Click on the Yes button to reboot the system so that the changes can take effect, or click on the No button so that you can make more changes to other CD-ROMs before rebooting system. Changes will not become effective until the system is rebooted.

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