Track Follower Alignment; Servo Head Alignment - HP 7925D Service Manual

7925
• Use the proper circumferential timing data graph.
The proper data graph is determined by:
(1)
The part number for the track follower on the
data graph matching the part number on track
follower PCA-A5 in the disc drive.
(2) The HP 13357A CE Disc Pack having a serial
number in the CE pack serial number range
indicated on the data graph.
The circumferential timing data graph is used as an aid to
determine the best solution to correct the circumferential
alignment. (Data graphs can be obtained from the field
service office.) To plot the data on the graph, proceed as
follows:
a. Perform the warmup procedure. (Refer to paragraph
3-13.) Perform the data head alignment check. (Refer to
paragraph 3-18.)
b. On the DSU, set the FUNCTION switch to position 4
(Cyl 0).
c. Select a head using the binary combination of toggle
switches H8, H4, H2, and HI on the DSU.
d. On the DSU, press the START pushbutton and note
the time on the digital display. Plot this value in the
proper location on the circumferential timing data
graph.
e. On the DSU, set the FUNCTION switch to position 5
(Cyl 410).
f. On the DSU, press the START pushbutton and note
the time on the digital display. Plot this value in the
proper location on the circumferential timing data
graph.
g. On the DSU, set the FUNCTION switch to position 6
(Cyl 820).
h. On the DSU, press the START pushbutton and note
the time on the digital display. Plot this value in the
proper location on the circumferential timing data
graph.
i. Repeat steps b through h for each data head.
After a data graph is completed for the disc drive under test,
follow the flowchart in figure 3-8. This flowchart is used in
conjunction with the description of circumferential timing
conditions, table 3-1, and the seven example data graphs,
figures 3-9 through 3-15, to determine the best solution to
correct the circumferential alignment.
A description of the seven possible conditions that can be
observed in the completed data graph for the disc drive
under test is contained in table 3-1.
Alignment and Adjustment
3-16. TRACK FOLLOWER ALIGNMENT. This
procedure should be performed only after the circumfer-
ential alignment shows that the disc drive is out of toler-
ance with a number 1, 2, 3, or 4 condition. (Refer to table
3-1.)
The alignment of the track follower PCA shifts all the
circumferential timing values by the same amount. The
amount of the shift is dependent on the adjustment of the
potentiometer, labeled IND DEL, on the track follower
PCA. To perform this alignment, proceed as follows:
a. Remove the exhaust shield (10, figure 6-1).
b. Perform the warmup procedure. (Refer to paragraph
3-13.)
c. Perform the circumferential alignment procedure.
(Refer to paragraph 3-15.)
d. On the data graph, identify the head and cylinder
position that is farthest out of tolerance (in the shaded
area) and set the DSU to this head (using the binary
combination of toggle switches H8, H4, H2, and HI)
and cylinder (Function Switch set to position 4, 5, or 6)
address.
e. Note the value on the data graph that is at the lower or
upper limit for the head and cylinder address identified
in step d.
f. On the DSU, press the start button.
g. As shown in figure 3-16, adjust the IND DEL potenti-
ometer on the track follower PCA until the value on the
DSU is within tolerance for the head and cylinder
selected.
h. Perform the circumferential alignment check. (Refer to
paragraph 3-14.) If the disc drive does pass, circumfer-
ential alignment is correct and the track follower PCA
is properly aligned. If the disc drive does not pass,
perform the circumferential alignment. (Refer to para-
graph 3-15.)
3-17. SERVO HEAD ALIGNMENT. Theservohead
normally requires alignment only after replacement. To
align the servo head, proceed as follows:
WARNING
Do not use any tools on the carriage
assembly while the heads are loaded
unless the DSU has just performed a
function 7 operation and the
5-second DSU head alignment cycle
time is completed. This precaution is
necessary to prevent the carriage
from emergency retracting and
damaging tools, or possibly causing
injury to personnel.
3-9