56FLOPPY DRIVE

TESTING AND ALIGNMENT

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CONTENTS AT A GLANCE

Floppy disk drives (Fig. 56-1) are basically electromechanical devices. Their motors,lead screws, sliders, levers, and linkages are all subject to eventual wear and tear. As a re-sult, a drive can develop problems that are caused by mechanical defects instead of elec-tronic problems. Fortunately, few mechanical problems are fatal to a drive. With theproper software tools, you can test a troublesome drive and often correct problems simplythrough careful cleaning and alignment. This chapter explains the concepts and proce-dures for floppy drive testing and alignment.

Understanding Alignment ProblemsRecognizing the problemsRepair vs. replaceTips to reduce floppy-drive problems

Using Alignment ToolsAdvanced tools

Aligning the DriveDrive cleaningClamping

Spindle speedTrack 00 testRadial alignmentAzimuth alignmentHead stepHysteresisHead width

Further Study

Understanding Alignment ProblemsThe causes behind floppy-drive alignment problems will vary somewhat depending on thedesign of the drive itself, but some common causes can crop up time after time:

■ Wear in the drive’s head positioning mechanism can eventually cause the radial align-ment to drift out of specification.

■ Various forms of debris often find their way into the drive’s mechanical parts and willoften accelerate wear in the drive—and in some cases, affect alignment directly bychanging the way that the drive’s sensors and mechanisms respond.

■ Dirt and normal wear might cause the head mechanism to not slide as easily as itshould. This puts an excessive load on the small stepper motor used to position theheads.

■ The read/write head assembly itself can become bent or otherwise damaged from acci-dental abuse—often not enough to cause a complete failure, but enough to significantlyaffect the alignment and cause problems when reading a diskette recorded by anotherdrive.

■ Drive alignment problems might also be revealed by marginal diskettes. If a drive isslightly out of alignment, it might work with a good data diskette, but not with a mar-ginal “cut priced” one.

RECOGNIZING THE PROBLEMS

As a technician, you will need to understand when a floppy drive is showing signs thatmight be related to alignment errors. In general, you should always respond to a chronicdrive error by examining the disk media itself. Slowly spin the disk and observe both sidesof the oxide layer. The layer should be smooth and even throughout—like the smooth sur-face of a quiet pond. If you see any marks or scratches on the disk, you should suspect thateither the R/W heads are misaligned or that a significant buildup of oxides are on the R/W

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FIGURE 56-1 A Teac FD-235 3.5" floppy drive. Teac America, Inc.

head(s). If you have not already cleaned the R/W heads as part of your regular repair prac-tices, clean them now. If the problem persists, the head assembly is probably severely mis-aligned and you should replace the drive or re-align it as you see fit.

Other classic indicators of alignment trouble are reading and writing errors. Data ischecked when it is read from or written to a drive. When you encounter a drive that hasdifficulty reading diskettes that were written on another PC (or writes diskettes that otherPCs have difficulty reading), the drive’s alignment is in serious doubt. Fortunately, align-ment software can test the drive and report on its specifications, allowing you to see anyunacceptable performance characteristics. If you find that the drive is faulty, you can thendecide to replace or re-align the drive at your discretion.

REPAIR VS. REPLACE

Floppy-drive alignment continues to be a matter of debate. The cost of a floppy-drivealignment package is often higher than the cost of a new drive. When compared withthe rising costs of labor and alignment packages, many technicians question the prac-tice of drive alignment when new drives are readily available. True, most casual PCenthusiasts would not choose to align a misbehaving drive. However, testing softwarehas an important place in any toolbox. At the very least, test software can confirm thefaulty alignment of a drive and eliminate the guesswork involved in drive replacement.For enthusiasts and technicians who have a volume of drives to service, alignment toolsoffer a relatively efficient means of recovering drives that might otherwise be dis-carded. Ultimately, one of a technician’s most vital tools is an open mind—you can re-pair or replace the drive, depending on what makes the most economic sense in yourparticular situation.

TIPS TO REDUCE FLOPPY-DRIVE PROBLEMS

Now that you’ve seen the most common causes of floppy-drive problems, you can recom-mend some pro-active steps to avoid or reduce problems in the future:

■ Keep the floppy drives clean Not only is it important to keep the drive’s R/W headsclean, but it is also important to keep dust and debris from accumulating inside thedrive’s mechanisms. A static-safe vacuum cleaner can usually remove unwanted dustor the debris can be removed by “blowing down” the drive with a can of electronics-grade compressed air and a long, thin nozzle.

■ Do not force disks in or out This is a classic cause of drive problems. Disks that be-come stuck in the floppy drive (usually because the drive does not release the 3.5"disk’s protective shroud properly) should be removed with the utmost care.

■ Keep air from circulating through the drive Floppy drives should generally be installedoutside of the normal air flow in a PC. This will reduce the amount of dust and debristhat normally flows around and through the drive.

■ Use good-quality diskettes “Bargain” diskettes often use inferior oxides, which tend torub off and accumulate on the R/W heads. If you encounter an unusual number of fail-ures with “bargain” diskettes, you should clean the R/W heads and switch to a betterbrand of diskettes.

1466 FLOPPY DRIVE TESTING AND ALIGNMENT

Using Alignment ToolsDrive alignment is not a new concept. Technicians have tested and aligned floppy drivesfor years using oscilloscopes and test disks containing precise, specially recorded data pat-terns. You might already be familiar with the classic “cat’s eye” or “index burst” align-ment patterns on oscilloscopes. This kind of manual alignment required you to find theright test point on your particular drive’s PC board, locate the proper adjustment in thedrive assembly, and interpret complex (sometimes rather confusing) oscilloscope displays.Traditionally, manual alignment required a substantial investment in an oscilloscope, testdisk, and stand-alone drive exerciser equipment to run a drive outside of the computer.

Although manual drive-alignment techniques are still used today, they are being largelyreplaced by automatic alignment techniques. Software developers have created interactivecontrol programs to operate with their specially-recorded data disks. These software toolkits provide all the features necessary to operate a suspected drive through a wide varietyof tests while displaying the results numerically or graphically right on a computer moni-tor (Fig. 56-2). As you make adjustments, you can see real-time results displayed on themonitor. Software-based testing eliminates the need for an oscilloscope and ancillary testequipment. You also do not need to know the specific signal test points for every possibledrive. Several popular tool kits are on the market, including FloppyTune by Data Depot,Inc. and DriveProbe (Fig. 56-3) by Accurite Technologies Inc. The contact informationfor both manufacturers is listed at the end of the chapter.

ADVANCED TOOLS

Although software tools make up a majority of the typical floppy-drive service options, thetools available to serious floppy-drive service technicians do not stop at software. Withthe proper supplemental test hardware (such as the Drive Probe Advanced Edition fromAccurite Technologies, Fig. 56-3), a PC can be turned into a comprehensive floppy-drive

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FIGURE 56-2 The DriveProbe automatic drive-test display.Accurite Technologies, Inc.

test bed that supports all types of standard PC drives, as well as Macintosh drives andmany types of floppy-disk duplicator drives.

Aligning the DriveAt this point in the chapter, you are ready to start the testing/alignment software and go towork. Before starting your software, however, you should disable any caching softwarethat will cache your floppy drive(s). Because caching software affects the way in whichdata is read or written to the floppy disk, caching will adversely affect the measurementsproduced by the alignment software. To ensure the truest transfer of data to or from thefloppy disk, boot the PC from a “clean” boot disk to disable all TSRs or device drivers inthe system. Once the alignment software is started, eight major tests gauge the perfor-mance of a floppy drive: clamping, spindle speed, track 00, radial alignment, azimuthalignment, head step, hysteresis, and head width. Remember that not all tests have adjust-ments that can correct the corresponding fault.

DRIVE CLEANING

Floppy-drive R/W heads are not terribly complex devices, but they do require precisionpositioning. Heads must contact the disk media to read or write information reliably. Asthe disk spins, particles from the disk’s magnetic coating wear off and form a deposit onthe heads. Accumulations of everyday contaminants, such as dust and cigarette smoke,

1468 FLOPPY DRIVE TESTING AND ALIGNMENT

FIGURE 56-3 DriveProbe: the advanced edition. Accurite

Technologies, Inc.

also contribute to deposits on the heads. Head deposits present several serious problems.First, deposits act as a wedge—forcing heads away from the disk surface, resulting in lostdata and read/write errors, and generally unreliable and intermittent operation. Depositstend to be more abrasive than the head itself, so dirty heads can generally reduce a disk’sworking life. Finally, dirty heads can cause erroneous readings during testing and align-ment. Because alignment disks are specially recorded in a very precise fashion, faultyreadings will yield erroneous information that can actually cause you to improperly adjustthe drive. As a general procedure, clean the drive thoroughly before you test or align it.

R/W heads can also be cleaned manually or automatically. The manual method is justas the name implies. Use a high-quality head cleaner on a soft, lint-free, anti-static swab,and scrub both head surfaces by hand. Wet the swab, but do not soak it. You might needto repeat the cleaning with fresh swabs to ensure that all residual deposits are removed. Becertain that all computer power is off before manual cleaning and allow a few minutes forthe cleaner to dry completely before restoring power. If you do not have head-cleaningchemicals on-hand, you can use fresh ethyl or isopropyl alcohol. The advantage to man-ual cleaning is thoroughness—heads can be cleaned very well with no chance of damagefrom friction.

Most software tool kits provide a cleaning disk and software option that allows you toclean the disk automatically. With computer power on and the software tool kit loaded andrunning, insert the cleaning disk and choose the cleaning option from your software menu.Software will then spin the drive for some period of time—10 to 30 seconds should be ad-equate, but do not exceed 60 seconds of continuous cleaning. Choose high-quality clean-ing disks that are impregnated with a lubricant. Avoid “bargain” off-the-shelf cleaningdisks that force you to wet the disk. Wetted cleaning disks are often harsh and prolongeduse can actually damage the heads from excessive friction. Once the drive is clean, it canbe tested and aligned.

CLAMPING

A floppy disk is formatted into individual tracks laid down in concentric circles along themedia. Because each track is ideally a perfect circle, it is crucial that the disk rotate evenlyin a drive. If the disk is not on-center for any reason, it will not spin evenly. If a disk isnot clamped evenly, the eccentricity introduced into the spin might be enough to allowheads to read or write data to adjoining tracks. A clamping test should be performed first,after the drive is cleaned because high eccentricity can adversely effect disk tests. Clamp-ing problems are more pronounced on 5.25" drives, where the soft mylar hub ring is vul-nerable to damage from the clamping mechanism.

Start your software tool kit from your computer’s hard drive, then insert the alignmentdisk containing test patterns into the questionable drive. Select a clamping or eccentricitytest and allow the test to run a bit. You will probably see a display similar to the one shownin Fig. 56-4. Typical software tool kits can measure eccentricity in terms of microinches-from true center. If clamping is off by more than a few hundred microinches, the spindleor clamping mechanisms should be replaced (be sure the diskette itself is not damaged).You can also simply replace the floppy drive. Try reinserting and retesting the disk sev-eral times to confirm your results. Repeated failures confirm a faulty spindle system.

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SPINDLE SPEED

Media must be rotated at a fixed rate in order for data to be read or written properly. Adrive that is too fast or too slow might be able to read files that it has written at that wrongspeed without error, but the disk might not be readable in other drives operating at a nor-mal speed. Files recorded at a normal speed also might not be readable in drives that aretoo fast or too slow. Such transfer problems between drives is a classic sign of speed trou-ble (usually signaled as “general disk read/write errors”). Drive speeds should be accurateto within ±1.5%, so a drive running at 300 RPM should be accurate to ±4.5 RPM (295.5 to304.5 RPM), and a drive running at 360 RPM should be accurate to within ±5.4 RPM(354.6 RPM to 365.4 RPM).

After cleaning the R/W heads and testing disk eccentricity, select the spindle speed testfrom your software menu. The display will probably appear much like the one in Fig. 56-5.Today’s floppy drives rarely drift out of alignment because rotational speed is regulated byfeedback from the spindle’s index sensor. The servo circuit is constantly adjusting motortorque to achieve optimal spindle speed. If a self-compensating drive is out of tolerance,excess motor wear, mechanical obstructions, or index-sensor failure is indicated. Checkand replace the index sensor or the entire spindle-motor assembly. You can also replacethe entire floppy drive outright.

TRACK 00 TEST

The first track on any floppy disk is the outermost track of side 0, which is track 00. Track00 is important because it contains the boot record and file-allocation information vital forfinding disk files. The particular files saved on a disk can be broken up and spread out allover the disk, but the FAT data must always be in a known location. If the drive cannotfind track 00 reliably, the system might not be able to boot from the floppy drive or evenuse disks. Floppy drives utilize a sensor, such as an optoisolator, to physically determinewhen the R/W heads are over the outermost track.

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FIGURE 56-4 Screen display from a DriveProbe eccentricitytest. Accurite Technologies, Inc.

Select the track 00 test from your software menu and allow the test to run. A track 00test measures the difference between the actual location of track 00 versus the point atwhich the track 00 sensor indicates that track 00 is reached. The difference should be lessthan ±1.5 mils (one-thousandths of an inch). A larger error might cause the drive to en-counter problems reading or writing to the disk. The easiest and quickest fix is to alter thetrack 00 sensor position. This adjustment usually involves loosening the sensor and mov-ing it until the monitor display indicates an acceptable reading. Remember that you onlyneed to move the sensor a small fraction, so a patient, steady hand is required. The track00 sensor is almost always located along the head-carriage lead screw. Mark the originalposition of the sensor with indelible ink so that you can return it to its original position ifyou get in trouble.

RADIAL ALIGNMENT

The alignment of a drive’s R/W heads versus the disk is crucial to reliable drive opera-tion because alignment directly affects contact between heads and media. If head con-tact is not precise, data read or written to the disk might be vulnerable. The radialalignment test measures the head’s actual position versus the precise center of the outer,middle, and inner tracks (as established by ANSI standards). Ideally, R/W heads shouldbe centered perfectly when positioned over any track, but any differences are measuredin microinches. A radial alignment error more than several hundred microinches mightsuggest a head-alignment error.

Select the radial alignment test from your software tool kit and allow the test to run. Atypical radial alignment test display is illustrated in Fig. 56-6. If you must perform an ad-justment, you can start by loosening the slotted screws that secure the stepping motor, andgently rotate the motor to alter lead screw position. As you make adjustments with the testin progress, watch the display for the middle track. When error is minimized on the innertrack, secure the stepping motor carefully to keep the assembly from shifting position. Use

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FIGURE 56-5 Screen display from a DriveProbe motor-speedtest. Accurite Technologies, Inc.

extreme caution when adjusting radial head position—you only need to move the head afraction, so a very steady hand is needed. You should also re-check the track 00 sensor tobe sure the sensor position is acceptable. If you are unable to affect radial head alignment,the drive should be replaced.

AZIMUTH ALIGNMENT

Not only must the heads be centered perfectly along a disk’s radius, but the heads mustalso be perfectly perpendicular to the disk plane. If the head azimuth is off by more thana few minutes (1⁄60 of a degree), data integrity can be compromised and disk interchange-ability between drives—especially high-density drives—might become unreliable. Whenthe heads are perfectly perpendicular to the disk (at 90 degrees), the azimuth should be 0minutes.

Select the azimuth test from your software tool kit and allow the test to run. Figure 56-7shows an azimuth-alignment test display. An azimuth-alignment test measures the rota-tion (or twist) of R/W heads in terms of + or – minutes. A clockwise twist is expressed asa plus (+) number, and a counterclockwise twist is expressed as a negative (–) number.Heads should be perpendicular to within about ±10 minutes. It is important to note thatmost floppy drives do not allow azimuth adjustments easily. Unless you want to experi-ment with the adjustment, it is often easiest to replace a severely misaligned drive.

HEAD STEP

The head step (or index step) test measures the amount of time between a step pulse fromthe coil-driver circuits and a set of timing mark data recorded on the test disk. In manualoscilloscope adjustments, this would be seen as the “index burst.” Average index time istypically 200 s for 5.25" drives, and 400 s for 3.5" drives. In automatic testing with yoursoftware tool kit, you will see time measurements for both heads on the inner and outertracks (Fig. 56-8). The actual range of acceptable time depends on your particular drive,but variations of ±100 s or more is not unusual.

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FIGURE 56-6 Screen display from a DriveProbe radial-alignment test. Accurite Technologies, Inc.

If the head step timing is off too far, you can adjust timing by moving the index sensor.As with all other drive adjustments, you need only move the sensor a small fraction, so beextremely careful about moving the sensor. A steady hand is very important here. Be sureto secure the sensor when you are done with your timing adjustments.

HYSTERESIS

It is natural for wear and debris in the mechanical head-positioning system to result in some“play”—that is, the head will not wind up in the exact same position moving from outsidein, as moving from the inside out. Excessive play, however, will make it difficult to find thecorrect track reliably. Testing is accomplished by starting the heads at a known track, step-ping the heads out to track 00, then stepping back to the starting track. Head position is thenmeasured and recorded. The heads are then stepped in to the innermost track, then back to

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FIGURE 56-7 Screen display from a DriveProbe azimuth-alignment test. Accurite Technologies, Inc.

FIGURE 56-8 Screen display from a DriveProbe index-to-datatest. Accurite Technologies, Inc.

the starting track. Head position is measured and recorded again. Under ideal conditions,the head carriage should wind up in precisely the same place (zero hysteresis), but naturalplay almost guarantees some minor difference. A typical hysteresis test-measurement dis-play is shown in Fig. 56-9. If excessive hysteresis is encountered, the drive should be re-placed because it is difficult to determine exactly where the excess play is causes in the drive.

HEAD WIDTH

Another test of a drive’s R/W heads is the measurement of their effective width. Effectivehead widths are 12 or 13 mils for 5.25" double-density drives, 5 or 6 mils for 5.25" high-density drives, and 4 or 5 mils for all 3.5" drives. As you run the head-width test with yoursoftware tool kit, you will see effective width displayed on the monitor (Fig. 56-10). As

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FIGURE 56-9 Screen display from a DriveProbe hystersistest. Accurite Technologies, Inc.

FIGURE 56-10 Screen display from a DriveProbe head-widthtest. Accurite Technologies, Inc.

R/W heads wear down, their effective width increases. If the effective width is too low,the heads might be contaminated with oxide buildup. When small head widths are de-tected, try cleaning the drive again to remove any remaining contaminates. If the widthreading remains too small (or measures too large), the heads or head carriage might bedamaged. You can replace the R/W head assembly, but often the best course is simply toreplace the drive outright.

Further StudyThat’s all for Chapter 56. Be sure to review the glossary and chapter questions on the ac-companying CD. If you have access to the Internet, take a look at some of these floppy-drive maintenance resources:

Accurite Technologies: http://www.accurite.com

Data Depot: http://www.datadepo.com

NEC: http://www.nec.com

FURTHER STUDY 1475

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