Warmup; Circumferential Alignment; Data Head Alignment Locations - HP 7925D Service Manual

7925 Alignment and Adjustment
c. On the disc drive, set the READ ONLY switch to the
protected position (.), the unit select switch to 0
(zero), and the RUN/STOP switch to RUN.
d. Set the DSU to function 3 and rotate the DELAY
control to a position near MIN. Press the START
pushbutton and allow the disc drive to perform ran-
dom seek operations for 5 minutes.
e. Set the DSU to function 7 and press the START
pushbutton. Allow the disc drive heads to remain
positioned at cylinder 490 for 15 minutes before
proceeding.
Note: Do not stop the spindle while the DSU is
set to FUNCTION 7. If the spindle must
be stopped, remove any tools from the
actuator assembly; set the DSU to
FUNCTION 1; press the START
pushbutton, then the STOP pushbutton;
and then set the RUN/STOP switch to
STOP.
REF 7311-52
Figure 3-5. Data Head Alignment Locations
3-13. WARMUP. The warmup is performed to allow
for temperature stablization before proceeding with head
alignment or head alignment check. To perform the warm-
up, proceed as follows:
a. Install the DSU as outlined in paragraph 3-9. Hook the
liquid crystal thermometer to the outside of the front
door (6, figure 6-1), as shown in figure 3-6.
b. Install the HP 7925 CE Disc Pack (13357 A) in the disc
drive.
REF 7301-80
Figure 3-6. Thermometer
Note: When the DSU is set to function 7 and
the START pushbutton is pressed, en-
sure the meter pointer moves to the far
right, then to the far left, and then back
again. If the meter does not act as de-
scribed, perform the servo head align-
ment. The time required for this cycle is
5 seconds. This operation is referred to as
the 5-second cycle throughout the
alignment procedures.
3-14. CIRCUMFERENTIAL ALIGNMENT
CHECK. This procedure is used to check the circumfer-
ential alignment of the data heads and the servo head.
Note: To test an HP 7925 Disc Drive, the DSU
must have a date code of 1845 or greater.
The date code is located on a tag on the
back of the DSU.
The HP 13357A CE Disc Pack has a circumferential timing
tolerance label attached to the outside cover. (Refer to fig-
ure 3-7.) The information on each label is divided into 3
rows and 9 columns. The columns labeled HO through H8
correspond to the number of the data head in the disc drive
selected by the DSU toggle switches. The rows 0, 410, and
820 are the cylinder numbers of the disc pack selected by
setting the DSU to positions 4, 5, or 6, respectively. The
label gives the range for the DSU digital display reading,
depending on the selection of the data head and the
cylinder position. The first number in each column is the
minimum acceptable digital display reading for the DSU.
The last number in each column is the maximum accept-
able digital display reading for the DSU.
The following procedure verifies circumferential align-
ment by ensuring that the DSU digital display reading is
within the range specified on the CE disc pack label.
3-7