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SERVICE MANUAL

7941 AND 7945
DISC DRIVES
Manual part no. 07940-90903
Microfiche part no. 07940-90803

PRINTED: SEP 1985 07940-90903
Prin ted in U.S.A E0985

FliD'l HEWLETT
~~ PACKARD
PRINTING HISTORY
New editions incorporate all update material since the previous edition. Updating Supplements, which are is-
sued between editions, contain additional and revised information to be incorporated into the manual by the
user. The date on the title page changes only when a new edition is published.

First Edition SEP 1984
Change 1 10 DEC 1984
Second Edition JAN 1985
Third Edition . SEP 1985

NOTICE
The information contained in this document is subject to change: without notice.

HEWLETT-PACKARD MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS
MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Hewlett-Packard shall not be
liable for errors contained herein or for incidental or consequential damages in connection with the furnish-
ing, performance or use of this material.

This document contains proprietary information which is protected by copyright. All rights are reserved. No
part of this document may be photocopied or reproduced without the prior written consent of
Hewlett-Packard Company.

COREFILE-FLITCORE

11
Fli:n- HEWLETT
~~ PACKARD

SERVICE MANUAL

7941 AND 7945
DISC DRIVES
Manual part no. 07940-90903
Microfiche part no. 07940-90803

PRINTED: SEP 1985 07940-90903
Printed in U.S.A E0985

Serial Number Prefix

The main part of this manual applies directly to HP 7941 and HP 7945 Disc Drives with serial numbers prefixed 2540 and
subsequent. RI~fer to Appendix B for disc drives with serial numbers prefixed 2515 and prior. Refer to Appendix A for disc
drives with sel"ial numbers prefixed 2438 and prior.

OPTIONS COVERED

In addition to the standard models, this manual
covers the following options: 01 5 and 550.

FOR U.S.A. ONLY

The Federal Communications Commission (in 47 CFR 15.838) has specified that the fol-
lowing notice be brought to the attention of the users of this product.

FEDERAL COMMUNICATIONS COMMISSION
RADIO FREQl!ENCY INTERFERENCE
STATEMENT

Warning: Thiis equipment generates and uses radio frequency energy and if not installed and used properly, that is, in
strict accordance with the manufacturer's instructions, may cause interference to radio and television reception. It has
been type tested and found to comply with the limits for a Class B computing device in accordance with the specifiu-
tions in Subpart J of Part 15 of FCC Rules, which are designed to provide reasonable protection against such inter-
ference in a I'esidential installation. However, there is no guarantee that interference will not occur in a particular in-
stallation. If this equipment does cause interference to radio or television reception, which can be determined by turn-
ing the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following
measures: reclrient the receiving antenna; relocate the computer with respect to the receiver; move the computer away
from the rec.liver; plug the computer into a different branch circuit. If necessary, the user should consult the dealer or
authorized field service representative for additional suggestions. The user may find the following booklet prepared by
the Federal (~ommDnications Commission helpful: "How to Identify and Resolve Radio-TV Interference Problems". This
booklet is aV:lilable from the U.S. Government Printing Office, Washington, DC 20402. Stock No. 004-000-00345-4.

HEWLETT -PACKARD COMPANY
P.O. BOX 39 BOISE, IDAHO 83707, U.S.A.
PRINTING HISTORY
New editions incorporate all update material since the previous edition. Updating Supplements, which are is-
sued between editions, contain additional and revised information to be incorporated into the manual by the
user. The date on the title page changes only when a new edition is published.

First Edition SEP 1984
Change 1 10 DEC 1984
Second Edition JAN 1985
Third Edition . SEP 1985

NOTICE
The information contained in this document is subject to change without notice.

COREFILE-FLITCORE

11
CONTENTS

Section I Page
GENERAL INFORMATION

Introductiorl 1 -1
Scope Of Manual 1-1
Options 1-2
Related Manuals 1-2
Characteristics 1-2

Section II Page
CHANNEL INTERFACE

Introduction . . . . . 2-1
CS/80 Instruction Set 2-1
Transaction Structure 2-1
Real Time Commands .. 2-1
Complementary Commands 2-1
General Purpose Commands 2-9
Diagnostic Commands . . . 2-9
Transparent Messages 2-9
Hewlett-Packard Interface Bus 2-9
HP-IB Communications 2-12
Channel Management . . . . . 2-13
Parallel Poll . . . . . . 2-13
Universal Device Clear 2-13
Message Structure 2-13

Section III Page
THEORY OF OPERATION

Introduction 3-1
Disc Format 3-3
SBC PCA-A5 . 3-5
SBC Internal Bus Architecture 3-5
HP-IB Data Bus . . . . . . . 3-6
RAM Di!lta Bus 3-6
Microprocessor Address Bus 3-6
Microprocessor Data Bus 3-6
DMA Gj!lte Array Data Bus 3-6
Read/Write Data Bus 3-6
Control/Status Data Bus 3-6
Control/Status Read Strobe 3-6
Control/Status Write Strobe 3-6
Control/Status Address Bus . 3-7

iii
CONTENTS (continued)

Read/Write Data Bus . . . . . . . . 3-7
Data Request In/Data Request Out 3-7
Data Strobe In/Data Strobe Out 3-7
HP-IB Interface IC . 3-7
Microprocessor 3-7
HP-IB Address Switch 3-7
Channel Status 3-7
Self-Test Switches 3-7
Self-Test Display 3-7
DMA Gate Array IC 3-8
RAM 3-8
EXEC ROM . . . . . . 3-8
DDC ROM . . . . . . . 3-8
Address Multiplexer 3-8
Clocks And Control Logic 3-8
Bu f f e rs . . . . . . . . . . . 3-8
Typical Host Dependent Transaction 3-8
Host Dependent to Device Dependent Communications 3-9
Control/Status Data and Address Buses 3-9
Read/Write Data Bus 3-9
Receiver/Driver . . . . . 3-9
Transceiver . . . . . . . 3-10
SBC/Disc Drive A1 Communication 3-10
Controller IC and Register Decode Logic 3-10
Self-Test Register . 3-10
GPC Register 3-10
DDC Errors Register 3-10
PUPO Register . . . 3-10
Disc Controller IC .. 3-10
Phase-Locked Loop IC 3-11
La tch . . . . . . . . . . 3-11
DMA Handshake Control 3-11
Clock Generator 3-11
Disc Drive A1 . . . . . . . 3-11
Disc Drive A1/SBC Control Communication 3-12
Input Buffers . . . . . . . . . . . . . . . 3-12
Output Drivers . . . . . . . . . . . . . . 3-12
Disc Drive A1/SBC Data Communication 3-12
Microprocessor and PLA ..... 3-13
Microprocessor/PLA Control Signals 3-13
Clock Generator 3-13
Head-Di sc Modu Ie .. 3-13
Actuator . . . . . 3-13
Recording Medium 3-13
Read/Write Heads 3-13
Read Preamplifier/Write Driver IC 3-14
Servo Head . . . . . . . 3-14
Servo Preamplifier IC . 3-14
Spindle Motor . . . . . . 3-15
Air Filtration Components 3-15

IV
CONTENTS (continued)

Actuator Lock Driver 3-15
Spindle Speed Control 3-15
Spindle Speed Checker 3-15
Spindle Motor Brake Relay and Relay Driver 3-15
Actuator Servo Control 3-15
Demodulator 3-16
Mode Select Switch 3-16
Seek Mode 3-16
Veloc i ty DAC .. 3-16
Tachometer . . . 3-16
Slope Selector 3-17
Current Inverter 3-17
On-Peak Detector 3-17
Power Amplifier 3-17
Inverter 3-17
Track-Follow Mode 3-17
Off-Track Detector 3-17
Seek Operation 3-17
Restore to Track 0 Operation 3-17
Read/Write Data Channel 3-18
Head Select and Control Logic . 3-18
Read Chain . . . . . . . . . . . 3-18
Amplifier/Signal Conditioner 3-18
Differential Line Driver 3-18
Write Chain 3-18
Line Receiver . . . . 3-18
Transition Generator 3-18
Write Current Source 3-19
Write Fault Detector 3-19
Self Test 3-19
Power-On Reset 3-19
Power Supply A4 3-19
AC Input Circuits 3-19
Switch-Mode Supply 3-20
Power-On Reset 3-20

Section IV Page
SERVICE IN1FORMATION

Introduction 4-1
Service Tools 4-1
FRA Locations 4-1
Cable Connectors 4-1
Signal Distribution 4-2
Power Distribution 4-2
Signal Notation 4-2
Block Diagram 4-2
Test Points .. 4-2

v
CONTENTS (continued)

Self-Test Controls 4-2
Fault/On Line Indicator 4-2
Sel f Test Swi tch .. 4-3
Self-Test Display 4-3
Display Results Switch 4-3
Internal Diagnostics 4-4
Sel f Tes t ...... . 4-4
Self-Test Subtests . 4-4
Self-Test Error Reporting 4-5
Fault/On Line Indicator 4-5
Self-Test Display 4-5
ReQuest Status 4-6
ReQuest Status Example 4-7
Run Time Error and Fault Reporting 4-8
External Exerciser 4-8
Amigo Clear (AMCLEAR) 4-8
Cancel Transaction (CANCEL) 4-8
Test HP-IB Channel (CHANNEL) 4-8
Channel Independent Clear (CICLEAR) 4-8
Clear Logs (CLEAR LOGS) . . . . . . . 4-8
Describe Selected Unit (DESCRIBE) 4-8
Perform Internal Diagnostics (DIAG) 4-8
Output Error Rate Test Log (ERT LOG) 4-9
Exit Program (EXIT) ..... 4-9
Output Fault Log (FAULT LOG) 4-9
Output Help Information (HELP) 4-9
Initialize Media (INIT MEDIA) 4-9
Update Device Logs (PRESET) .. 4-9
ReQuest Status (REQSTAT) . . . . 4-9
Perform Read-Only Error Rate Test (RO ERT) 4-10
Output Run Log (RUN LOG) . . . . . 4-10
Spare (SPARE) . . . . . . . . . . . . 4-10
Output Spare Table (SPARE TABLE) 4-10
Output Device Table (TABLES) 4-10
Perform Servo Test (SERVO) 4-10
Set Unit Number (UNIT) 4-10
Perform Write-Then-Read Error Rate Test (WRT ERT) 4-10
Troubleshooting 4-10

Section V Page
REMOVAL AND REPLACEMENT

Introduction 5-1
Preparation for Service 5-1
Removal And Replacement 5-2
Top Shroud . . . . . . 5-2
ROM Removal . . . . . 5-2
FRA5 (Single Board Controller PCA-A5) 5-2

vi
CONTENTS (continued)

Front Panel 5-3
Fan . . . . . . . . . . . . . . . . . 5-3
FRA4 (Power Supply Assembly A4) 5-4
FRA1 (Disc Drive Assembly A1) . 5-4

Section VI Page
REPLACEABLE PARTS

Introduction 6-1
Ordering Information 6-1

Section A Page
APPENDIX A

Backdating Information (Serial Numbers Prefixed 2438 and prior) . . . . . . . . . . . . . . A-1

Section B Page
APPENDIX B

Backdating Information (Serial Numbers Prefixed 2515 and prior) ........... B-1/8-2

Section C Page
APPENDIX C

Service Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1/C-2

vii
ILLUSTRATIONS

Figure Page

Transaction Structure . . . . . . . . . . . . . . 2-10
Hewlett-Packard Interface Bus Signal Lines 2-11

Disc Recording Format . 3-4
Track Recording Format . 3-5
Disc Drive, Block Diagram 3-29/3-30
Disc Drive, Functional Block Diagram, (Sheet 1 of 3) 3-31/3-32
Disc Drive, Functional Block Diagram, (Sheet 2 of 3) 3-33/3-34
Disc Drive, Functional Block Diagram, (Sheet 3 of 3) 3-35/3-36

Self-Test Controls and Readout 4-11
P8 Signal Source (Sheet 1 of 3) 4-19
P8 Signal Source (Sheet 2 of 3) 4-20
P8 Signal Source (Sheet 3 of 3) 4-21
Field Replaceable Assembly (FRA) Locations 4-26
FRAl (Disc Drive Al), Layout and Cable Connections 4-27
FRA4 (Power Supply A4), Layout and Cable Connections 4-28
FRA5 (SBC PCA-A5), Layout and Cable Connections 4-29
FRA4 (Power Supply A4), Test Points and Voltages 4-30
Cabling Diagram 4-31/4-32
Signal Distribution . 4-33/4-34

Order of Disassembly 5-5/5-6

Disc Drive, Exploded View 6-3

Appendix A Illustrations A-3

Appendix B Illustrations B-7

Vlll
TABLES

Table Page

Disc Drive Characteristics 1-3/1-4

Device Command Summary. . 2-2
Disc Drive Utilities .. . 2-9
HP-IB Def ini tions . . . . 2-12
Universal Command Formats. 2-12
HP-IB Message Structure. 2-14

Lis t 0 f Mn emo n i c s. . . . . 3-21

Single-Board Controller (Unit 2)
Self-Test Subtest List . . . 4-12
Disc Drive (Unit 0) Self-Test Subtest List. 4-13
Disc Drive Error Condition List. 4-18
Fault Code List .. 4-22
Diagnostic Summary . . . . . 4-25

Disc Drive Replaceable Parts. 6-2
Abbreviaticlns . . . " . . . . 6-4
Code List of Manufacturers 6-5/6-6

Appendix A Tables. A-4

Appendix B Tables. B-8

ix
SAFETY CONSIDERA TIONS

GENERAL - This product and related documenta- BEFORE APPLYING POWER - Verify that the
tion must be reviewed for familiarization with product is configured to match the available main
safety markings and instructions before operation. power source according to the input power con-
figuration instructions provided in this manual.

SAFETY SYMBOLS If this product is to be operated with an autotrans-
former make sure that the common terminal is
Instruction manual symbol: the connected to the earth terminal of the main power
product wIll be marked with this source.
symbol when it is necessary for
the user to refer to the instruc- SERVICING
tion manual in order to protect
the prod uc t against damage.
WARNING
Any servicing, adjustment, main-
Indicates hazardous voltages. tenance' or repair of this product
must be performed only by service-
trained personnel.

- Indica tes earth (ground) terminal. Adjustments described in this
manual may be performed with
power supplied to the product while
The WARNING sign denotes a protective covers are removed.
WARNING hazard. It calls attention to a Energy available at many points
procedure or practice which, if may, if contacted, result in per-
not correctly performed or ad- sonal injury.
he red to, could result in personal
injury. Do not proceed beyond a Capacitors inside this product may
WARNING sign until the indi- still be charged after the product
cated conditions are fully under- has been disconnected from the
stood and met. main power source.

To avoid a fire hazard, fuses with
The CAUTION sign denotes a the proper current rating and of
CAUTION hazard. It calls attention to an the specified type (normal blow,
opera ting procedure or practice time delay, etc.) must be used for
which, if not correctly performed replacement.
or adhered to, could result in
damage to or destruction of part To install or remove a fuse, first
or all of the product. Do not disconnect the power cord from the
proceed beyond a CAUTION sign device. Then, using a small flat-
until the indicated conditions are bladed screw driver, turn the
fully understood and met. fuseholder cap counterclockwise
until the cap releases. Install
SAFETY EARTH GROU~D - This is a safety either end of a properly rated fuse
class I product and is provIded with a protective into the cap. Next, insert the fuse
earthing terminal. An uninterruptible safety earth and fuse holder cap into the
ground must be provided from the main power fuseholder by pressing the cap in-
source to the product input wiring terminals, ward and then turning it clockwise
power cord, or supplied power cord set. Whenever until it locks in place.
it is likely that the protection has been impaired,
the product must be made inoperative and be
secured against any unintended operation.

x
GENERAL INFORMATION -
[ IJ
1 -1. INTRODUCTION desk-height stand-alone cabinet designed to hold
the disc drive and other desktop stack modules. A
The Hewlett -, Packard 7941 and 7945 Disc Drives kit for rack mounting the disc drive in a standard
are medium performance, random access, data EIA equipment rack is also available.
storage devic~~s designed for use with small and
medium sized. computer systems. The formatted This manual provides all the service information
storage capacities of the HP 7941 and HP 7945 are needed to maintain the disc drive. Details of the
24 megabytes and 55 megabytes, respectively. In control functions provided by the host computer
this manual, unless otherwise specified, "disc drive" are described in the installation documentation
'refers to both the HP 7941 and HP 7945. provided with the computer.

The disc driv

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