Troubleshooting; Diagnostic Test Programs; Troubleshooting Flowcharts; Power Sources - HP 7925D Service Manual

WARNING
TROUBLESHOOTING
I~
4-2. TROUBLESHOOTING
FLOWCHARTS
This disc drive does not contain
operator-serviceable parts. To pre-
vent electrical shock, refer all instal-
lation and maintenance activities to
service-trained personnel.
This section contains information useful for trouble-
shooting the HP 7925 Disc Drive. Included are functional
diagrams, troubleshooting flowcharts, wiring diagrams,
and test waveforms. The information provided is for the
isolation of malfunctions within the drive and not for
equipment external to the drive.
4-1. DIAGNOSTIC TEST PROGRAMS
Diagnostic test programs for use with Hewlett-Packard
systems containing disc drives are available from
Hewlett-Packard. It is recommended that the user of an
HP 7925 Disc Drive installed in a non-HP system have
available a diagnostic test program with capabilities simi-
lar to those offered by Hewlett-Packard.
An HP-generated diagnostic tests the system devices
which are associated with disc drive operation. In addition
to this testing capability, the diagnostic can also be used to
isolate a group of circuits within the drive as the possible
cause of a malfunction. These include the read/write cir-
cuits, the head positioning circuits, and the head and sec-
tor storage circuits. It should be noted that the diagnostic
is the only readily available means by which the user can
check the ability of the read/write circuits to write data on
the disc surfaces, read it back from the disc surfaces, and
store and retain the data. The disc service unit (DSU) will
not issue a write command and does not check data gener-
ated by the drive in response to a read command.
The diagnostic is also able to determine the status of the
drive (drive busy, not ready, seek check, first status, and
attention). It also monitors the on/off status of the DRIVE
FAULT indicator (fault).
The diagnostic can also be employed to detect patterns
exhibited by intermittent errors. This may be done by
running the diagnostic continuously over a period of time
and checking for the conditions present at each occurrence
of the error.
Detailed operating instructions for HP-supplied diag-
nostic test programs are contained in the documentation
delivered with the software.
If a malfunction can be associated with a certain circuit
through knowledge of the drive, the service-trained and
equipped user can go directly to the appropriate trouble-
shooting flowchart (figures 4-2 through 4-21) and follow-
ing the instructions given, attempt to remedy the fault.
Visual indication of the drive status, as described in table
4-1, is intended to aid in isolating the malfunction to a
particular area of the drive. If the malfunction cannot be
located in this manner, carry out the procedure described
in the power-up flowchart (figure 4-1). Failing this, the
diagnostic test program should be used to isolate the fault.
It should be noted that the power-up flowchart checks, in
general, operation of the blower, power sources, door lock
circuits, spindle rotating circuits, and head positioning
circuits. The diagnostic test program, on the other hand,
checks operation of the I/O control circuits, read/write
circuits, sector sensing circuits, and the portions of the
head positioning circuits that seek to a cylinder addressed
by the disc controller. Refer to table 4-3 for a description of
the symbols used on the troubleshooting flowcharts.
4-3. POWER SOURCES
The troubleshooting procedures in this section assume
that all power sources in the drive are within tolerance. If
they are not, the cause of the trouble will be apparent (IL
LED indicator lit) and the PSU LED on drive control
PCA-A4 will be off. If the +5 Vdc power source exceeds
approximately +5.6 Vdc, a crowbar circuit on PCA-A7
disables the 5-volt supply, causing all. indicators to be
extinguished. The mainframe assembly wiring diagram
(figure 4-23) can be used to trace power source malfunc-
tions. To check the voltages, proceed as follows:
WARNING
The following procedure is per-
formed with power supplied to the
disc drive, and protective covers re-
moved. This troubleshooting should
be performed only by service-trained
personnel who are aware of the
hazards involved (for example, fire
and electrical shock).
a. If applicable, remove the disc pack from the disc drive.
b. Remove ac power from the disc drive.
c. Remove the shroud as outlined in paragraph 5-3.
4-1