Fra Locations; Cable Connections; Signal Distribution; Power Distribution - HP 7942 Service Manual

Service Inf orma tion
7942 and 7946
4- 3. FRA LOCA TIONS
The locations of the field replaceable assemblies
(FRA's) identified by the self -test diagnostics are
shown in figure 4-4. Refer to section V for FRA
removal and replacement instructions and to sec-
tion VI for FRA iden tif ica tion and ordering in-
formation.
Note: The following FRA's contained
within tape drive assembly
U 1 - FRA 1 are not shown in detail
in figure 4-4. For their location,
refer to the Tape Drive Service
Manual, Section VI, Replaceable
Parts.
• U I-FRA3 (read/write assembly)
• U 1- FRA 7 (servo assembly)
• U I-FRA8 (head stepper motor)
• UI-FRA9 (capstan motor and
tachometer)
4-4. CABLE CONNECTIONS
An overall cabling diagram of the disc/tape drive
is provided in figure 4-11. The pin assignments
for the cable assemblies shown in figure 4-11 are
as detailed in figure 4-11 and Tape Drive Service
Manual, with the exception of power cable assemb-
ly WI. Details of how cable WI supplies voltages
from power supply assembly A4 to the components
of the drive are shown in figure 4- 5. Cable con-
nections to power supply assembly A4 are shown in
figure 4- 5.
Also, DC-IB cable assembly W2 in the drive has an
extra connector, allowing DC-IB signals to be con-
nected in parallel to both DDC's. The pin assign-
ments for the connectors on W2 remain as
described in the Tape Drive Service Manual.
4-5. SIGNAL DISTRIBUTION
Cable connections between the FRA's in the disc
drive are shown in figure 4 - 11. The distribution of
signals via these cables is shown in figure 4-12.
The mnemonics appearing in figure 4-12 are
defined in table 3-1.
4-2
4-6. POWER DISTRIBUTION
Details of ac input wiring and dc power distribu-
tion are shown in figure 3-4 and in figure 4-11.
4-7. SIGNAL NOTATION
In the disc drive logic circuits, a digital signal is
applied to its destination in one of two states: ac-
tive or inactive. The signal is active when its volt-
age level (high or low) makes the action occur for
which the signal was designed. This action is usual-
ly identified by a signal mnemonic. Refer to table
3-1. A mnemonic with an "-L" suffix indicates a
logic signal with an active low voltage level. A
mnemonic with an "-H" suffix indicates a logic
signal with an active high voltage level. Signal
mnemonics without an "-L" or "-H" suffix usually
indica te analog, data bus, or control bus signals.
4-8. BLOCK DIAGRAM
Block diagram of the disc/tape drive and disc drive
are provided in section III of this manual. (See
figures 3-3 and 3-4.) To facilitate references to
the three sheets of disc drive functional block
diagram (figure 3- 5) each sheet is identified by a
large bold numeral in the lower right-hand corner
of the page. These numerals are boxed in text and
table references, for example:
m.
Included in
figure 3 - 5 are diagrams for host dependent con-
troller FRA5
m,
device dependent controller
FRA2
III,
and disc drive assembly FRA 1
III·
Each of these diagrams in section III is accom-
panied by a circuit description.
4-9. POWER SUPPLY A4
A number of test points are provided in power
supply assembly A4 for troubleshooting and test
purposes. The locations of these test points are
shown in figure 4 -7. Also provided are details of
the voltages monitored at the test points.
It
should
be noted that access to the test points requires the
removal of the front panel assembly from the
drive. Refer to section V for removal details.
Note: Power supply assembly A4, part no.
07942-60024, used in the drive is a
higher wattage unit than power