1 Top 2
3
10 4
5
8
6 7
Bottom
9
Figure 5.1 A typical 3 1/2-inch floppy disk drive.
1. 34-pin data cable connector 2. 4-pin power connector 3. Head-actuator motor
4. Worm gear to drive actuator motor 5. Read-write head (one of two)
6. Write-protect sensor
7. Media sensor (720KB or 1.44MB) 8. Spindle (left) and drive motor (right) 9. Disk ejector button
10. Logic board
Where Floppy Drives Fail—and Simple Fixes
I spent several years on the road carrying around disassembled PCs for use in computer-troubleshooting classes. Typically, I had more floppy-drive failures than about anything else, due to the combina-tion of inexperienced students, rough handling by airline baggage carousels, and the simple fact that a floppy drive is designed to be used within the confines of a computer case. I learned how to fix drives the hard way—when the only spare I had wasn’t working, either.
The Drive Cover
The drive cover acts as a dust cover, which is obviously a good idea for a drive that uses exposed, relatively soft flexible magnetic media. However, a damaged or bent drive cover can bind the disk ejector, preventing it from moving. The drive cover can easily be removed and bent back into shape.
The Stepper Motor
The stepper motor moves the head actuator across the surface of the floppy disk media, reading or writing data (see Figure 5.2).
Worm gear Head
assembly Mounting screw
Head mount
Head flex cable
Guide shaft
Head connector
Stepper motor
Figure 5.2 An expanded view of a stepper motor and head actuator.
On a 3 1/2-inch drive, the stepper motor is often a worm-gear arrangement rather than the band drive that was used on the older 5 1/4-inch drives. The worm gear is very compact, but can be jammed by shock. To free it up, carefully unscrew the stepper motor from the rear of the drive frame and move the head actuator back and forth
gently until the worm gear moves freely again. Reassemble the drive and test it outside the case by running the data and power cable to it before you secure it into its normal position.
Interface Circuit Boards
A drive’s interface circuit board (also called logic board) can be dam-aged by shock, static electricity, or a power surge. Usually, it can easily be removed from the bottom of the drive and replaced by a spare circuit board from an identical drive with a bad read/write head or stepper motor. Keep such failures around for spare parts.
Read/Write Heads
Because of the contact between the heads and disk, a buildup of the magnetic material from the disk eventually forms on the heads.
The buildup should periodically be cleaned off the heads as part of a preventive-maintenance or normal service program.
The best method for cleaning the heads involves the use of a com-mercial wet-method disk head cleaner and a program that spins the cleaning disk and moves the heads around the cleaning media.
MicroSystems Development (www.msd.com) offers the TestDrive floppy drive testing program, which contains such a cleaning util-ity. Depending on the drive use and the amount of contaminants (smoke, dust, soot) in the air, you should clean the read/write heads on a floppy drive only about once every six months to a year.
Do not use standard 3 1/2-inch floppy head cleaners with LS-120 SuperDisk floppy drives; although these drives can read and write to standard disks as well as the 120MB SuperDisk media, a conven-tional cleaner will damage their special read/write heads. Check www.superdisk.comfor a SuperDisk-compatible cleaning kit.
Floppy Drive Hardware Resources
Whether they are built in or not, all primary floppy controllers use a standard set of system resources:
• IRQ 6 (Interrupt Request)
• DMA 2 (Direct Memory Address)
• I/O ports 3F0-3F5, 3F7 (Input/Output)
These system resources are standardized and generally not change-able. This normally does not present a problem because no other devices will try to use these resources (which would result in a con-flict).
Floppy Drives 145
Don’t Use a Floppy Drive While Running a Tape Backup About the only circumstance that would cause a hardware conflict is the use of a floppy drive while a tape backup is running. While most high-capacity tape backup drives today no longer use the floppy interface, they still often use DMA 2 for fast data transfers.
Because DMA transfers are not checked by the CPU or any other part of the system, simultaneous use of DMA 2 by a tape backup and a floppy drive can easily result in data loss on either or both media types.
Disk Drive Power and Data Connectors
Two sizes are used for disk drive power connectors. Figure 5.3 shows the original “Molex” power connector used on 5 1/4-inch floppy drives. Most 3 1/2-inch floppy drives and tape backups use a smaller connector, but either size normally has the same 4-wire pinout shown in the figure.
1 2 3 4
(+5V) Red (Gnd) Black (Gnd) Black
(+12V) Yellow
2 1 4 3
Figure 5.3 A disk drive female power supply cable connector.
Some 3 1/2-inch tape drives come with an extension cable with only two wires: a ground wire (black) and a +5v wire (red), because their motors use the same +5v power as the logic board does.
Figure 5.4 shows a typical 5-connector floppy data cable. Typically, the 5 1/4-inch edge connectors are seldom used today, unless a 3 1/2-inch drive has a pin-to-edge connector adapter attached.
Table 5.1 compares floppy and hard disk ribbon cables.
Figure 5.4 Standard five-connector floppy interface cable.
Table 5.1 Comparing Ribbon Cables—Floppy Versus Hard Disk Interface
Type Floppy ST-506 ESDI IDE SCSI
Cable 34-pin 34-pin 40-pin or 50-pin or
Width 80-strand 68-pin
Notes Almost all have Can be straight 80-strand cable twist between A: or twisted; twist has 40 pins;
drive connectors away from pin 1; designed for and B: drive obsolete and use with connectors; twist seldom seen UDMA/66 toward pin 1 today; used motherboards (colored edge with 20-pin and drives of cable) ribbon cable
Table 5.2 lists the parameters for current and obsolete disk drives used on PCs. If you are preparing a drive with FORMAT that is smaller than the drive’s capacity, you will need to set the FORMAT parameters manually.
A damaged media descriptor byte will prevent programs from prop-erly accessing the disk; however, this problem can be fixed with Norton Utilities.
Table 5.2 Floppy Disk Logical Formatted Parameters
Current Formats Obsolete Formats Disk Size 3 1/2 3 1/2 3 1/2 5 1/4 5 1/4 5 1/4 5 1/4 51/4 (inches)
Disk Capacity 2,880 1,440 720 1,200 360 320 180 160
(KB)
Media F0h F0h F9h F9h FDh FFh FCh Feh
Descriptor Byte
Sides (Heads) 2 2 2 2 2 2 1 1
Floppy Drives 147
Pin 1 (Colored Wire)
Pin 34
“Twist”
Motherboard Connector
5.25" Drive “B” Connector
3.5" Drive “A”
Connector
5.25" Drive “A”
Connector 3.5" Drive “B” Connector
Table 5.2 Floppy Disk Logical Formatted Parameters Continued Current Formats Obsolete Formats
Tracks per 80 80 80 80 40 40 40 40
Side
Sectors per 36 18 9 15 9 8 9 8
Track
Bytes per 512 512 512 512 512 512 512 512
Sector
Sectors per 2 1 2 1 2 2 1 1
Cluster
FAT Length 9 9 3 7 2 1 2 1
(Sectors)
Number of 2 2 2 2 2 2 2 2
FATs
Root Dir. 15 14 7 14 7 7 4 4
Length (Sectors)
Maximum Root 240 224 112 224 112 112 64 64
Entries
Total Sectors 5,760 2,880 1,440 2,400 720 640 360 320
per Disk
Total 5,726 2,847 1,426 2,371 708 630 351 313
Available Sectors
Total 2,863 2,847 713 2,371 354 315 351 313
Available Clusters
Floppy Drive Troubleshooting
Table 5.3 Floppy Drive Troubleshooting Tips
Problem Cause Solution
Dead drive—the Bad power supply Measure the power at the cable with a drive does not or power cable. voltmeter; ensure that 12v and 5v are
spin and the LED available to the drive.
never comes on.
Drive or controller Check BIOS setup for proper drive type not properly and ensure the controller is enabled if configured in BIOS built in to the motherboard; if an add-on setup. card contains a floppy controller and the motherboard also has one, disable one or the other.
Bad data cable. Replace the cable and retest.
Defective drive. Replace the drive and retest.
Defective controller. Replace the controller and retest. If the controller is built into the motherboard, disable it via the BIOS setup, install a card-based controller, and retest, or replace the entire motherboard and retest.
Table 5.3 Floppy Drive Troubleshooting Tips Continued
Problem Cause Solution
Drive LED remains Data cable is on Reinstall the cable properly and retest.
on continuously. backward at either the drive or controller connection.
The data cable Reinstall the cable properly and retest;
could be offset on replace cable if this doesn’t work.
the connector by one or more pins.
Phantom Defective cable. Replace the cable and retest.
directories—you
have exchanged Improper drive Older drives must have their DC jumper disks in the drive, configuration. (for Drive Changeline support) enabled.
but the system
still believes the Defective drive or Replace the drive and retest.
previous disk is interface.
inserted, and even shows directories of the previous disk.
Note
Windows users: Windows does not automatically refresh the dis-play with File Manager, Explorer, and so on by default. Use the F5 key or click Refresh to re-read the disk.
Common Floppy Drive Error Messages—Causes and Solutions
Table 5.4 Handling Floppy Drive Error Messages
Error Message Cause Solution
Invalid Media or You are formatting the Make sure you are using the Track Zero Bad, disk and the disk media right type of disk for your drive Disk Unusable type does not match and formatting the disk to its
the format parameters. correct capacity.
Defective or damaged Replace the disk and retest.
disk.
Dirty read/write heads. Clean drive, allow heads to dry, and retest.
CRC Error or The data read from the Replace the disk and retest.
Disk Error 23 disk does not match the Clean the drive heads, allow them data that was originally to dry, and retest. Use Norton written. (CRC stands for Utilities or SpinRite to recover data Cyclic Redundancy Check.) from disk.
Floppy Drives 149
Table 5.4 Handling Floppy Drive Error Messages Continued
Error Message Cause Solution
General Failure The disk is not formatted Reformat the disk and retest.
Reading Drive A, or has been formatted for Abort, Retry, Fail, a different operating system or Disk Error 31 (Macintosh, for example).
Damaged areas on the Replace the disk and retest. Use disk medium. Norton Utilities or SpinRite to
recover data from disk.
Disk not seated properly Remove and reinsert in drive. Try in drive. holding disk in place with your
hand. If you can read the data, copy it to a reliable disk.
Access Denied You are trying to write Move the write-protect switch to to a write-protected disk allow writing on the disk, or or file. remove the read-only file attribute
from the file(s). File attributes can be changed by the ATTRIB com-mand or through the file properties in Windows.
Insufficient Disk The disk is filled, or the Check to see if sufficient free space Space or Disk Full root directory is filled. is available on the disk for your
intended operation. Use folders on the disk to store files, or change to a new disk.
Bytes in Bad Displayed after FORMAT, Operating system will not use bad Sectors CHKDSK, or SCANDISK if sectors, but this is a sign of a (greater than 0) allocation units (clusters) marginal disk; reformat or discard
have been marked bad. and use a new disk with no bad sectors.
Disk Type or You are attempting to Disks can be copied only between Drive Type DISKCOPYbetween two drives using the same disk density Incompatible incompatible drive and size. Use COPY or XCOPY unless
or Bad disk types. you are trying to create an exact
copy.