Special Tools; Diagnostic Techniques; Introduction; Soft Error" Detection And Correction - Zenith Z-100 PC series Service Manual

5.1.3 Special Tools
The following special tools are available for performing maintenance on the SA455/465.
Description
Part Number
SA128 Alignment Diskette
54573
SA126 Alignment Diskette 54382
Exerciser PCB 54157
Head Cable Extender 54578
Phillips Screw Drivers Medium and Small
Oscilloscope T extronix 465 or equivalent
5.2 DIAGNOSTIC TECHNIQUES
5.2.1 Introduction
Incorrect operating procedures, faulty programming, damaged diskettes, and "soft errors" created by airborne con ­
taminants, random electrical noise, and other external causes can produce errors falsely attributed to drive failure
or misadjustment. Unless visual inspection of the drive discloses an obvious misalignment or broken part. attempt
to repeat the fault with the original diskette, then attempt to duplicate the fault on a second diskette.
5.2.2 "Soft Error" Detection and Correction
Soft errors are usually caused by:
a.
Airborne contaminants that pass between read/write heads and disk. Usually these contaminants
can be removed by cartridge self-cleaning wiper.
b. Random electrical noise that usually lasts for a few microseconds.
c. Small defects in written data and/or track not detected during write operation may cause soft er­
rors during read.
d. Improper grounding of power supply, drive, and/or host system. Refer to SA455/465 OEM
manual
(PIN
39238) for proper grounding requirements.
e. Improper motor speed.
The follOWing procedures are recommended to recover from the above mentioned soft errors:
a. Reread track 10 times or until such time as data is recovered.
b. If data is not recovered after using step (a), access head to adjacent track in same direction
previously moved, then return to desired track.
c. Repeat step (a).
d. If data is not recovered, error is not recoverable.
5.2.3 Write Error
If
an error occurs during a write operation, it will be detected on the next revolution by doing a read operation,
commonly called a "write check." To correct the error, another write and check operation must be done. If the
write operation is not successful after 10 attempts have been made, a read operation should be attempted on
another track to determine if the media or the drive is failing. If the error persists, the diskette should be replaced
and the above procedure repeated. If the failure still exists, consider the drive defective. If the failure disappears.
consider the original diskette defective and discard it.
5-2
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