Air Circulation And Filtration System - HP 7925D Service Manual

Theory of Operation
7925
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).
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:
1-61.
AIR CIRULATION AND
FILTRATION SYSTEM
• 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 1-6, steps 1 through
8, for the specific events.
The air circulation and filtration system (see figure 1-11)
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 1-11, 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 developed air flow bypasses the absolute filter
element, passing 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
I~ --:"":"":"'~_ ABSO LUTE
FILTER
PREFILTER
ENCLOSURE
PREFILTER
7301-45
1·30
Figure 1-11. Air Circulation and Filtration System