Servo Amplifier Adjustment - HP 7901A Operating And Service Manual

Maintenance
OSCILLOSCOPE SETUP :
TIME BASE.
VERTICAL SENSITIVITY
7901-28
2 MS/CM
2
V/CM
Figure 5-6. Encoder Alignment Waveform
c. Set the C BAL variable resistor on encoder assembly A9
at midrange.
d. Set the VEL COM variable resistor on sector cylinder
assembly A11 fully counterclockwise; then advance it
1/4 turn clockwise.
e. Retract the carriage and turn off disc drive power.
f.
Connect the disc service unit to the disc drive. (Refer to
HP 132 19A Disc Service Unit Operating and Service
Manual.)
g. Connect linear motor L4 to A4P6 test plug on servo
amplifier regulator assembly A4.
Note : Current is limited to the linear motor
while in the TEST position, preventing
possible damage to the motor during
adjustments .
h. Remove the carriage detent. (See figure 5-7.)
i. Install cartridge receiver and a disc cartridge. Restore
disc drive power.
j. Ensure that the RESET DRIVE FAULT switch on the
disc service unit is on. Set the disc drive LOAD switch
on.
Note: After 30 seconds, the carriage will extend
to the home position (cylinder 000).
k. Connect the oscilloscope to channel C amplifier output
A9TP2.
I. Adjust the C BAL variable resistor to obtain an oscillo-
scope deflection of 0 ±0.1 volts.
5-10
7901A
Figure 5-7 . Carriage Detent
m. Using the disc service unit, perform one -cylinder
increment tests to ensure that the cylinder addressing
circuitry is functional.
n. Press the LOAD switch to the released position and
remove disc drive power.
o. Reconnect linear motor L4 to connector A4P5 on servo
amplifier regulator assembly A4 .
p. Remove disc cartridge and cartridge receiver.
q. Install the carriage detent and replace receiver and disc
cartridge.
r. Perform the servo amplifier adjustment procedure.
5-40. SERVO AMPLIFIER ADJUSTMENT.
5-41. To adjust the servo amplifier, proceed as follows :
a. Connect the disc service unit to connector A5J4 of the
disc drive. (Refer to HP 13219A Disc Service Unit
Operating and Service Manual.)
b. Apply power to the disc drive and press the LOAD
switch.
c. Set the RESET DRIVE FAULT switch of the disc
service unit to ON.
d. Set the ACCESS MODE switch of the disc service unit
to the INCREMENTAL SEEK position and the DRIVE
OPERATION control switch
to
ALLOW ACCESS
mode. Press RUN switch.