HP 7925D Service Manual page 77

7925
Table 4-1. Visual Indication of Drive Status
Troubleshooting
ACTIVE STATE
INDICATOR!
FUNCTIONAL
INDICATION
DIAGRAM
LOGIC EQUATION
CIRCUIT DESCRIPTION
Unit Select Identifi- SEL Indicator is lit when both of the following conditions are
I/O Control System,
cation Indicator met:
figure 4-24.
a. Control bus bits DO thru D2 match signals USO thru
US2 from UNIT SELECT switch S3.
b. Select flip-flop is set. [ADU (Address Unit) signal
selected on tag bus while STROBE signal is active
sets flip-flop.]
READ ONLY R01 Indicator is lit when READ ONLY switch S5 is set to Read/Write System,
Indicator READ ONLY.
ftgure 4-28.
DOOR UNLOCKED PSF. (STOP. CRB. SPD) Indicator is lit when all of the following conditions are met Spindle Rotation
Indicator (door unlock solenoid energized): System, figure 4-25.
a. RUN/STOP switch S2 set to STOP.
b. Carriage fully retracted.
c. Spindle stopped.
d. All power supplies are on.
DRIVE READY
Set
=
AGC • CB Indicator is lit when both of the following conditions are Head Positioning
Indicator
Reset
=
FLT
+
DL. PIP met: System, figure 4-26.
+
SPU
+
STOP
a. AGC (Automatic Gain Control) signal active.
b. SB (Servo Balanced) signal active.
DRIVE FAULT
FLTL
=
AGC
+
CBF
+
Indicator is lit when anyone of the following conditions is Head Positioning
Indicator
TO
+
ILF
+
W • AC
+
met: System, figure 4-26.
W • AR
+
R • W
+
MH
+
a. AGC (Automatic Gain Control) signal active, caused
DCW
by loss of servo information any time after drive be-
comes active.
b. CB (Carr iage Back) signal active, caused by defective
carriage back detector (phototransistor). This occurs
when drive is ready but the phototransistor or CB sig-
nals say that heads are retracted.
c. TO (Time Out) caused by anyone of the following:
1. Any head loading sequence or recalibration taking
more than 1.25 seconds.
2. Track-to-track seek taking more than 120 milli-
seconds.
d. ILF (Interlock) signal active, due to one of the following:
1. Out of tolerance or missing power supply voltage.
2. Excessive temperature condition, as sensed by
switch A9A1.
3. PCA improperly seated or missing.
4. Line voltage 15 percent below nominal value.
5. Current limit in spindle power amplifier.
e. Destructive write faUlt, caused by anyone of the
following:
•
1. Drive
lQ..
write mode with no data signal applied
(W • AC LED indicator is lit.)
2. More than one head selected for reading or
writing. (MH LED indicator is lit.)
3. DC write current is supplied to the head driver
while drive is not in write mode. (Both MH and
W. AC LED's are lit.)
4-3