HP 7942 User manual

HEWLETT-PACKARD
HP 7942 AND HP 7946 DISC/T APE DRIVES
SERVICE MANUAL

CERTIFICATION
Products, materials, parts, and services furnished on this order
have been provided in accordance with all applicable Hewlett-
Packard specifications. Actual inspection and test data per-
taining to this order is on file and available for examination.
Hewlett-Packard's calibration measurements are traceable to
the National Bureau of Standards to the extent allowed by the
Bureau's calibration facilities.
The Hewlett-Packard Quality Program satisfies the require-
ments of FAR 52.246-15.

rlin- HEWLETT
.:~ PACKARD
SERVICE MANUAL
7942 AND 7946
DISC/T APE DRIVES
Manual part no. 07942-90903
Microfiche part no. 07942-90803
PRINTED: FEB 1987
Printed in U.S.A.
Serial Number Prefix
07942-90903
E0287
The main part of this manual applies directly to HP 7942 and HP 7946 Disc/Tape Drives with serial numbers prefixed 2615
and subsequent. Refer to Appendix A for serial numbers prefixed 2614 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 FREQUENCY INTERFERENCE
STATEMENT
Warning: This equipment generates and uses radio frequeucy energy and if not installed and used properly, that is, in
strict accordalllce with the manufacturer's instructions, may cause interference to radio and television reception. It has
been type test.~d and found to comply with the limits for a Class B computing disc/tape drive in accordance with the
specifications in Subpart J of Part 15 of FCC Rules, which are designed to provide reasonable protection against such
interference ill a residential installation. However, there is no guarantee that interference will not occur in a par-
ticular install~ltion. If this equipment does cause interference to radio or television reception, which can be determined
by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the fol-
lowing measures: reorient the receiving antenna; relocate the equipment with respect to the receiver; move the equip-
ment away from the receiver; plug the equipment into a different branch circuit. If necessary, the user should consult
the dealer or 3,uthorized field service representative for additional suggestions. The user may find the following booklet
prepared by tllte Federal Communications Commission helpful: "How to Identify and Resolve Radio-TV Interference
Problems". This booklet is available from the U.S. Government Printing Office, WashingtoD, 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
..
Second Edition
Third Edition .
FEB 1985
AUG 1986
FEB 1987
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-PARCORE
11

PREFACEI
This publication provides field service information for the HP 7942 and HP 7946 Disc/Tape Drives. 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 consists of a 55-megabyte disc drive and a tape drive combined
in a similar manner.
This publication
is divided into the following parts:
• Section I - Contains a general description of the disc/tape drive.
• Section II -Provides references to the CS/80 Instruction Set commands applicable to the disc/tape drive.
• Section III -- Describes the operating principles of the disc/tape drive.
• Section IV -- Contains servicing information for the disc/tape drive.
• Section V - Supplies step-by-step removal and replacement procedures for field replaceable assemblies
and parts in the
disc/tape drive.
• Section VI -- Lists and illustrates the field replaceable assemblies and parts in the disc/tape drive.
• Appendix A-Contains removal and replacement and relaceable parts for disc/tape drives with serial
number prefix 2614 and prior.
• Tape Drive -Consists of a Tape Drive Service Manual. This manual provides detailed service informa-
tion for the tape drive portion of the disc/tape drive.
iii/iv

Section I
GENERAL INFORMATION
Introduction
Documentation
Related Manuals
Options
Ch ar act eri st il cs
Section II
CHANNEL INTERFACE
Introduction ...... .
CS/80 Instruction Set
Transaction Structure
Real Time Commands
Complementary Commands
General Purpose Commands
Diagnostic Commands ..
Transparent Messages .
Hewlett-Packard Interface Bus
HP-IB Communications
Channel Management
Paralll~l Poll
Universal Device Clear
Message Structure
Section III
THEOR Y OF OPERATION
Introduction
Disc Drive Introduction
Disc Format ........ .
HOC peA-AS ......... .
HOC Internal Bus Architecture
HP-IB Data Bus ........ .
RAM Data Bus .
Microprocessor Address Bus
Microprocessor Data Bus
DMA Gate Array Data Bus
Read/Write Data Bus
Data/Control Interface Bus
Control/Status Data Bus
Control/Status Read Strobe
Control/Status Write Strobe
CONTENTS
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CONTENTS (continued)
Control/Status Address Bus
Select .............. .
Read/Write Data Bus
Data Request In/Data Request Out ...... .
Da ta St robe In/Da ta St robe Ou t ........ .
HP-IB
Interface IC ., ................ .
Microprocessor .....
HP-IB Address Switch
Channel Status ...
Sel f Tes t Swi tches ....................................... .
Self Test Display . . . . . . . . . . . . . . . . . . . . . . .............. .
DMA Ga te Array IC . . . . . . . . . . . . . . . . . . . . . . ..... .
RAM ........... ...................... . .............. .
EXEC EPROM . . . . .. ...................... . .............. .
DOC 0 EPROM ......................................... .
DOC 1 E PROM .................................. , . . . . .
Address Multiplexer ........................................ .
Clocks And Control Logic .................................... .
ROM Sw i t ch . . . . . . . . . . . . . . . _. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Buffers
Typical HOC Transaction ..................................... .
DOC PCA-A2 ................................................. .
HOC/DOC Commu ni cat ion .................. . . . . . . . . . . . . . . . .
Control/Status Data and Address Buses ..................... .
Read/Wri
te Data Bus ..................................... .
Receiver/Driver ........................................ .
Transceivers .......................... . .............. .
DOC/Disc
Drive A1 Communication ............. . .............. .
Controller IC and Register Decode Logic ....... . .............. .
HDA Desc r ipt ion PROM ..................................... .
Self-Test Register ....................... . ......... .
GPC Register ........................................... .
DOC Err 0 rs Reg i s t er ..................................... .
PUPO Register ........................... . ..... .
Disc Controller IC .................... . ......... .
Phase- Loc ked Loop IC ....................................... .
Latch ................................................... .
DMA Handshake Cont rol ...................................... .
Clock Generator ......................................... .
Write Precompensation .................................... .
Disc Drive A1 ............................................. .
Disc Drive A1/DDC Control Communication ...................... .
Input Buffers .......................................... .
Output Drivers .......................................... .
Disc Drive A1/DDC Data Communication ........................ .
Microprocessor and PLA ..................................... .
Microprocessor/PLA Control Signals .......................... .
Clock Generator ........................................... .
Head-Disc Module .......................................... .
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Actuator .....
............................ 3-15
vi

Recording Medium ............ .
Read/Wri te Heads ............ .
Read Preamplifier/Write Driver IC
Servo Head ........ .
Servo Preamplifier IC .
Spindle Moto r ...... .
Air Filtration Components
Actuator Lock Driver .
Spindle Speed Control
Spindle Speed Checker
Spindle Motor Brake Relay and Relay Driver
Actuator Servo Control
Demodu la to r ..... .
Mode Select Switch
Seek
~Iode
Velocity DAC
Tachometer .,
Slclpe Selector
Current Inverter
On-Peak Detector
Power Amplifier
Inverter ..... .
Track--Follow Mode .
Off-Track
Detector
Seek Operation
Restore to Track 0 Operation
Read/Wri t.e Data Channel .....
Head SelE!ct and Control Logic .
Read Chain ............ .
Ampli f
ier/Signal Condi tioner ..
Differential Line Driver
Wri te Chain ........ .
Line Receiver .... .
Transition Generator
Write Current Source
Write
Fault Detector
Sel f test ...... .
Power Supph' A4
AC Input Circuits
Swi tch-Mc)de Supply
Power-On Reset ....
Section IV
SERVICE INI4'ORMATION
Introduction
Service Tools
FRA Locations
CONTENTS (continued)
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vii

CONTENTS (continued)
Cable Connections ..
Signal Distribution
Power Distribution
Signal Notation
Block Diagram ..
Power Supply A4
HDC PCA-AS ... .
Self Test .... .
Self-Test Controls
Tape Drive FAULT Indicator
Tape Drive BUSY Indicator
Disc Drive FAULT/ON LINE Indicator
Se 1f T est Sw i tch ....
Self-Test Display
DISPLAY RESULTS Switch
Internal Diagnostics
Sel f Test ........... .
Self-Test Subtests
Self-Test Error Reporting
Fault/On Line Indicator
Self-Test Display ... .
Request
Status ..... .
Request
Status Example
Run Time Error and Fault Reporting
External Exerciser ........ .
Amigo Clear (AMCLEAR)
Cancel Transaction (CANCEL)
Test HP-IB Channel (CHANNEL)
Channel Independent Clear (CICLEAR)
Clear Logs (CLEAR LOGS) ........ .
Describe Selected Unit (DESCRIBE) .
Perform
Internal Diagnostics (DIAG)
Output Error Rate Test Log (ERT LOG)
Exit Program (EXIT) ....... .
Output Fault Log (FAULT LOG) .
Output Help Information (HELP)
Initialize Media (INIT MEDIA)
Update Device Logs (PRESET)
Request Status (REQSTAT) ....
Perform Read-Only Error Rate Test (RO ERT)
Output Run Log (RUN LOG) ..... .
Spare Sector (SPARE) ........ .
Output Spare Table (SPARE TABLE)
Output Device Table (TABLES)
Perform Servo Test (SERVO)
Set Unit Number (UNIT) ...... .
Perform Write-Then-Read
Error Rate Test (WRT ERT)
Troubleshooting
Disc Drive Maintenance
Tape Drive Maintenance .
viii
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