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Functional Description
7936 and 7937
MNEMONIC
TERR2-L
TRKCR-H
UNDER
VLT-L
US
WC
5-68
SIGNAL
Timing
Error 2*
Track
Crossing*
Under
Voltage
Unsafe
Write
Current
Table 5-l. List of Mnemonics (21 of 23)
SOURCE
IIA1
II A1
~A1
WI]
A3
IDII
A2
DESCRIPTION
DEDICATED SERVO TIMING AND PLL
output to FAULT LATCHES.
TERR2-L
is
the output of a circuit that monitors the sync
bit to make sure that it falls within a
specified window and is followed by a
specified gap.
TERR2-L
can be monitored at pin 35 of the
servo test point PCA.
TRACK CROSSING DETECTOR output to
SERVO CONTROLLER.
TRKCR-H
goes
high when a dedicated servo code track is
crossed.
TRKCR-H
can be monitored at pin 50 of the
servo test point PCA.
Output
from
UNDERVOLTAGE
DETECTOR.
UNDER VLT-L
signals to the
servo power amplifier CONTROL AND
FAULT INDICATION circuit that a failure
has occurred in either the +45V or -45V sup-
ply to the amplifier.
READ PREAMP/WRITE DRIVER IC out-
put line in which current flows whenever
writing is enabled and there is an absence of
write current or data transitions.
Possible
causes include:
•
One or both sides of selected head open
•
One or both sides of selected head shorted
•
Insufficient write current to heads
•
Failure to select write mode.
US
is
connected
to
the
UNSAFE
DETECTOR in read/write PCA-A2 via HDA
cable W8.
WRITE CHAIN output line which sends cur-
rent
to
the
READ
PREAMP/WRITE
DRIVER ICs during a write.
WC
is
connected
to
the
READ
PREAMP/WRITE DRIVER ICs in HDA A3
via HDA cable W8.
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