HP 7942 Service Manual page 60

Theory of Operation
7942 and 7946
MNEMONIC
us
VCMA, VCMB
WC
WFLT-L
3-28
Table 3 -1. List of Mnemonics (Continued)
SIGNAL
U nsaf e Current
Actuator Voice
Coil Drive
W ri te Current
Write Fault
SOURCE
Al
III
lA
III
lA
III
At
III
DESCRIPTION
A read preamplifier/write driver line
in which current flows whenever
writing is enabled and there is an ab-
sence of write current or data transi-
tions.
Drive current to actuator voice coil.
Signal is supplied by actuator servo
control circuit.
A line from the write current source
sending current to the read/write
head during a write. Output to the
read preamplifier/write driver IC's.
ST- 506 Interface control signal.
WFL T - L warns that a condition ex-
ists in disc drive assembly A 1 which
makes writing unsafe. Output to DDC
PCA-A2
III
via cable W3. Signal
becomes acti ve for the following
reasons.
WRITING:
• Open head.
• Shorted head.
• Improper write current.
• An off -track condition occurs.
• Invalid or multiple heads are
selected.
• Spindle speed loss when writing.
• A write is attempted when
SKCMP-L is inactive (high).
• Write gate but no write data.
• Attempting to write with
RDY -L inactive (high).
• A write attempted when the disc
drive is write protected with
the write protect option.
READING:
• Write current appears at head.
Disc drive assembly A 1 will not ac-
cept further commands after a write
fault has been detected by the micro-
processor.