Dsu Operation; Head Alignment Meter Calibrations - HP 7925D Service Manual

Maintenance
The labels S32, S16, S8, S4, S2, and Sl are used with the
manual function. The toggle switches select the desired
sector for operation.
The right-hand column of labels is used in the manual
mode. Switches T1 through T3 set the tag bus commands
and switches CO through C15 set the control bus
commands.
LED Indicators - Twenty indicators used in conjunction
with the toggle switches. When a switch is set to the right,
the corresponding LED lights indicating that the switch
line is active. The indicators also display the states of the
tag bus and control bus.
STOP Pushbutton - Momentary contact switch that stops
an operation in progress.
START Pushbutton - Momentary contact switch that
starts an operation, or in the manual mode, provides the
strobe (STB) as long as actuated.
DELAY Control - Varies time between seek operations
from one millisecond (MIN) to 1.2 seconds (MAX).
Digital Display - Three-digit display that indicates head
offset in 6.3 microinch increments. If head offset is out of
range, two decimal points on the left and center digits
light. For seek operations, the display reads out time in
milliseconds.
HEAD ALIGNMENT Meter - Analog meter is used dur-
ing head alignment. The meter displays head offset in
6.3-microinch increments. Each minor division represents
12.5 microinches. (See figure 2-3.)
7925
2-9. DSU OPERATION. The operating functions
of the DSU using the controls and indicators are described
in the following paragraphs.
FUNCTION 1 - ALTERNATE SEEK. This function is
used to exercise the disc drive. The toggle switches are
used to select the cylinder addresses for the seek opera-
tion. The top 10 switches are used to select the first cylin-
der address and the bottom 10 switches are used to select
the second cylinder address. When the START pushbutton
is pressed, the heads seek home (cylinder 0) then go to the
first cylinder address. When the heads reach the first
address, a seek to the second address is performed. This
operation continues until the STOP pushbutton is pressed
or the function is changed. If either address is greater than
822 the heads will remain at the address within range. If
both addresses are out of range, only the seek home opera-
tion will be performed. Seek delay time is adjusted by the
DELAY control.
Note: All operations are terminated when the
FUNCTION switch is set to any other
position.
FUNCTION 2 - INCREMENTAL SEEK. The bottom
10 switches are used to set the address increment the drive
will seek. When the START pushbutton is pressed, the
heads seek home and then will proceed to the next ad-
dress. The next address is determined by the present ad-
dress plus the address number set on the toggle switches.
The incremental seek begins at cylinder zero and progres-
ses to the next higher address until the highest cylinder
number selected is an out-of-range address. When the
out-of-range address is reached, the next seek will be the
present address less the number set on the toggle
switches. Seek delay time is adjusted by the DELAY
control.
~
,I-.--
62.5 MICROINCHES
I"
III
I 10
1 DIVISION
=
12.5 MICRO INCHES
I-n--/
1/2 DIVISION
=
6.3 MICROINCHES
I
o
\ \
~o
\ 30
"-
50
1~
/ /
30 /
/
50
FUNCTION 3 - RANDOM SEEK. Cylinder addresses
are generated with a pseudo random sequence provided by
the DSU. When the START pushbutton is pressed, the
heads seek home then progress through the random
sequence. The sequence continues until the STOP
pushbutton is pressed or the function is changed. The seek
time delay is adjusted by the DELAY control.
--- - -,-
-.
- - -
--
7301-29
Figure 2-3. Head Alignment Meter Calibrations
2-6
FUNCTIONS 4, 5, and 6 - INDEX SEQUENCES. These
functions are used for the circumferential alignment of the
heads.
FUNCTION 7 - HEAD ALIGNMENT. This function is
used to align the data heads. The data head offset to be
displayed on the meter and digital display are selected by
the four toggle switches denoted by H8 (C11), H4, H2, and
HI. When the START pushbutton is pressed, the heads
seek home then seek to track 490. The head offset is
displayed in 6,3-microinch units on the meter and digital
display.