HP 7942 Service Manual page 15

GENERAL INFORMA TION
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1-1. INTRODUCTION
The Hewlett'-Packard 7942 and 7946 Disc/Tape
Drives are medium performance, random access,
data storage devices designed for use with small
and medium sized computer systems. The HP 7942
consists of a 24-megabyte disc drive and a tape
drive combined in a single desktop cabinet to form
an integrated disc/tape drive. The HP 7946 con-
sists of a 55-megabyte disc drive and a tape drive
combined in a similar manner. In this manual, un-
less otherwise specified, "drive" refers to both the
HP 7942 and HP 7946.
The 24- and 55-megabyte disc drives employ two
and four non removable 130-millimetre
(5.l2-inch) discs, respectively, for storage media.
Each disc surface employs one movable head to
service its data tracks. The bottom surface of the
lowest disc in the stack contains continuous
prerecorded servo data which is used to ensure the
precise positioning of the read/write heads.
Head positioning is accomplished by a rotary ac-
tuator and closed loop servo positioning system.
Mechanical and contamination protection for the
discs, heads, and the rotary actuator is provided by
a sealed head-disc module. The head-disc module
includes a slelf -contained air filtration system
which supplies clean air and equalizes temperature
throughout the module.
The tape drive is a data storage device utilizing a
removable 1/ 4-inch tape cartridge. Two tape
lengths are available: 150 feet (16.7 megabyte) and
600 feet (67 megabyte). The tape drive functions
as a back -up device for the disc drive. The data
transfer rate for back -up is approximately two
megabytes per minute. (The actual data transfer
rate is host dependent.) The tape drive includes a
read -after-write capability for data verification,
as well as data recovery and automatic sparing.
The tape drive is compatible with existing
1/4-inch cartridge tape drives contained in other
HP disc/tape drives.
Also included in the drive are a Hewlett-Packard
Interface Bus (HP-IB)* controller and a power
supply.
The drive contains internal self -test diagnostics
and a fault-finding system which exercise key
functions of the drive. Self test is performed au-
tomatically at power on and can also be initiated
by the host or by a switch on the rear panel of the
drive. Go/no-go test results are indicated by
green/red indica tors on the f ron t panel. If a
failure occurs, information on the cause of the
failure can be determined by viewing a 2-digit
numeral display on the rear panel. Fault isolation
is to a unit level (disc drive, tape drive, controller,
and power supply), followed by field replaceable as-
sembly or assemblies within the identified unit.
Details of subtest failures are also provided.
The drive is packaged in a stand -alone desktop
cabinet. Accessories available include a desk-
height stand -alone cabinet designed to hold the
drive and other desktop stack modules. A kit for
rack mounting the drive in a standard EIA equip-
ment rack is also available.
1 - 2. DOCUMENT A TION
The documentation provided in this publication is
divided into two parts. The first part, H
P 7942
and 7946 Disc/Tape Drives Service Manual,
(Sections I through VI) provides details of how the
disc drive and tape drive are combined in a single
cabinet to form an integrated disc/tape drive.
Information provided includes circuit description,
servlclng details, removal and replacement
procedures, and replaceable parts information.
Detailed information on the disc drive theory of
operation, service information, and replaceable
parts is also provided. The second part, identified
by the liT APE DRIVE" tab, contains service
documentation for the tape drive.
*Not just IEEE-488, but the hardware, documentation and support that delivers the shortest path to a
computation system.
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