HP 7925D Service Manual page 210

7925
• DRIVE FAULT lamp lights (FLTL = 0).
• Drive fault status bit becomes active (status bit 5
= 1).
The R • W fault flip-flop is reset by NDPS whenever the
power-on sequence is initiated (lLF
=
1), the RUN/STOP
switch is set to RUN (RUN
=
1), or a CPS command is
decoded (CPS
=
1).
A-64. Destructive Write Faults. The three fault
conditions classified as destructive are:
• A write gate without any alternating write current
(W.AC).
• More than one head selected (MH).
• DC write current without a write gate (DC. W).
In the first condition, the state of the ACW signal is
continually monitored. If the ACW signal remains inac-
tive (ACW
=
0)
during the write mode (WRITE
=
1) and
no write faults exist (WFLT
=
1), a W • AC fault is de-
clared. When a W. AC fault is detected, the following
events will occur:
• W. AC fault flip-flop is set (W • AC • WFLT
=
1).
• WAFL signal becomes active (WAFL = 0).
• W. AC fault LED lights (WAFL
=
0).
• DWF signal becomes active (DWF
=
0),
• WFLT signal becomes active (WFLT
=
0).
• Subsequent read/write faults are inhibited
(WFLT
=
0).
• Heads are unloaded. Refer to table A-6, steps 1 through
8, for the specific events.
The W • AC fault flip-flop is reset by DPS whenever the
power-on sequence is initiated (ILF = 1) or the RUN/
STOP is set to RUN (RUN
=
1).
In the second condition, the state of the MHS signal is
continually monitored. If the MHS signal becomes active
(MHS
=
0) and no other write faults exist (WFLT
=
1), a
MH fault is declared. When a MH fault is detected, the
following events will occur:
• MH fault flip-flop is set (MHS • WFLT = 1).
• MHFL signal becomes active (MHFL
=
0).
• MH fault LED lights (MHFL
=
0).
• DWF signal becomes active (DWF
=
0).
• WFLT signal becomes active (WFLT
=
0).
Appendix A
• Subsequent read/write faults are inhibited
(WFLT
=
0).
• Heads are unloaded. Refer to table A-6, steps 1 through
8, for the specific events.
The MH fault flip-flop is reset by DPS whenever the
power-on sequence is initiated (ILF
=
1) or the RUN/
STOP switch is set to RUN (RUN
=
1).
In the third condition, the state of the DCW signal is
continually monitored. If write current is being applied to
the heads (DCW
=
1), the disc drive is not in the write
mode (WRITE
=;
0), and no other write faults exist
(WFLT
=
1), a DC. W fault is declared. When a DC. W
fault is detected, the following events will occur:
• Both the W • AC and MH fault flip-flops are set (DC.
W. WFLT
=
1).
• Both the
WAFL
and MHFL signals become active
(WAFL and MHFL
=
0).
• Both the W • AC and MH fault LED's light (WAFL and
MHFL
=
0).
• DWF signal becomes active (DWF = 0).
• WFLT signal becomes active (WFLT
=
0).
• Subsequent read/write faults are inhibited
(WFLT
=
0).
• Heads are unloaded. Refer to table A-6, steps 1 through
8, for the specific events.
The W. AC and MH fault flip-flops are reset by DPS
whenever the power-on sequence is initiated (lLF
=
1) or
the RUN/STOP switch is set to RUN (RUN
=
1).
A-65. AIR CIRULATION AND
FILTRATION SYSTEM
The air circulation and filtration system (see figure A-9)
consists of a rotating impeller located on the disc drive
mainframe and an exhaust fan located on the power panel
assembly. In addition, a prefilter and absolute filter are
used to trap contaminants in the developed air supply.
As can be seen in figure A-9, a centrifugal blower draws
room ambient air into the prefilter enclosure through the
vent openings in the front door of the enclosure. The larger
airborne contaminants are trapped as the air is drawn
through the prefilter. Approximately one-half of the de-
veloped air flow bypasses the absolute filter element, pass-
ing directly through the lower half of the absolute filter
box. From there, the air is directed through a flexible hose
to the cooling air duct where it is diverted into three
separate paths. Two of these paths flow along the fins of
A-29