HP 7970B, 7970C Operating And Service Manual

~--------------------HEWLETTiPPACKARD--------------------~

OPERATING

7970B/7970C

DIGITAL

AND

MAGNETIC

TAPE TRANSPORT

Prin ted-Circuit Assemblies:

07970-60481, Series 1101 07970-61010, Series 1323 07970-61020, Series 1229 07970-61080, Series 1042 07970-61150, Series 1049 07970-62172,Series1322 07970-62173, Series 1329 07970-62086, Series 1013 07970-62089, Series 1206

SERVICE

PART

2

TAPE

MANUAL

UNIT

07970-90383

Copyright 11000

Wolfe

HEWLETT-PACKARD

Road,

Cupertino,

COMPANY

California

95014,

1972

U.S.A.

PRINTED: AUG 1973

7970B/7970C

Description

SECTION

DESCRIPTION

1-1.

1-2. This section describes the transport for the HewlettPackard vides a functional description critical assemblies are defined and optional assemblies are described.

1-3.

1-4. The tape unit consists sembly and a sheet metal housing assembly. The housing assembly contains the power supply, the power distribution assembly, the control and status assembly, and interfacing provisions. The read and write modules are also contained in the housing assembly.

1-5. The transport casting assembly consists moving assemblies, reel motors, capstan servo motor, sion arm assemblies and the circuits associated with these assemblies. The magnetic tape head assembly, photosense assembly, write interconnect assembly, and read fier assembly are also mounted sembly. mounted are accessible and assembly open.

INTRODUCTION.

7970B/7970C Digital Magnetic Tape Units and pro-

of

the transport circuits. Speed

PHYSICAL DESCRIPTION.

of

a transport casting

to

the transport casting

All

standard and optional switch assemblies are

to

the transport casting assembly.

all

circuits will operate with the transport

All

assemblies

of

all tape

ten-

preampli-

as-

1-10.

1-11. Capstan Motor Assembly MG1, 60140, 10 ips and 37.5 ips. Capstan Motor Assembly MG1, part number 07970-60141, ranges between 37.6 ips and 45 ips.

1-12.

1-13. The capstan servo connector dummy connector pending upon the speed range motor A9

CAPSTAN MOTOR ASSEMBLY.

part

number 07970-

is

used on tape units with tape speed ranges between

is

used on tape units with tape speed

Note

Capstan Motor Assembly MG1, part number 07970-60140, may be used ating

at

45 ips. However, program restrictions

must be maintained.

CAPSTAN SERVO PRINTED-CIRCUIT ASSEMBLY.

that

functions

is

installed in one

assembly used. See figure 7-10, Capstan Servo PCA

Schematic Diagram, for details

CAUTION

on

tape units oper-

PCA

is

equipped with a dummy

as

a strapping network. The

of

six positions, de-

of

the tape unit and capstan

of

dummy connector.

1-6. SPEED

1-7. The tape 10

ips and 45 ips. The actual tape speed

fied when the unit

to

critical

1-8. REEL MOTORS.

1-9. Reel Motors B1/B2, part number 07970-60170, are used on tape units with tape speed ranges between and 37.5 ips. Reel Motors B1/B2, part number are used on tape units with tape speed ranges between 37.6 and 45 ips.

Part 2

tape speed:

Reel Motor Assembly.

a.

Capstan Motor Assembly.

b. c. Capstan Servo

Magnetic Tape Head Assembly.

d.

Read Modules.

e. f.

Write Modules.

CRITICAL

unit

will operate

is

ordered. The following are limited or

PC

ASSEMBLIES.

at

Assembly.

tape speeds between

of

the unit

07970-60171,

is

speci-

10

ips

Ensure

that

dummy connector proper position prior unit. Attempting to operate the unit without the connector installed wrong position may result in damage

1-14.

1-15. The magnetic tape head assembly consists guides, a tape cleaner, and, depending upon configuration, read, write, and erase heads. The tape head assembly critical; refer of

1-16. READ MODULES.

1-17. The read modules are described in detail in part 3 or

1-18. WRITE MODULES.

1-19. The write modules are described in detail in of

MAGNETIC

to

section VI for

the magnetic tape head assembly.

part 5 of

this manual.

to

or

with the connector in the

TAPE HEAD ASSEMBLY.

is

installed in the

applying power

part

numbers and speed ranges

to

the unit.

to

the

is

of

speed

part

tape

1-1

4

Description

7970Bj7970C

1-20. BASIC AND OPTIONAL ASSEMBLIES.

1-21. The tape unit tions. Regardless basic and applicable

a. Transformer Assembly. b.

Photosense Assembly. c. Tension Assemblies (two). d. Capstan Assembly. e.

Reel Motor Assemblies (two). f.

Reel Servo Printed-Circuit Assembly. g.

Capstan Servo Printed-Circuit Assembly.

Control and Status Printed-Circuit Assembly.

h.

is

available in a variety

of

tape speed, the following assemblies are

to

all tape units.

of

configura-

i. Power Distribution Assembly. j. Power Regulator Printed-Circuit Assembly.

1-22. The control switch assembly however, if the tape unit

is

equipped with write data cir-

cuits, the control switch assembly

is

a basic assembly;

wHi

contain the write en-

able indicator.

1-23. The following assemblies are optional and, depend-

of

ing upon the use of

the tape unit.

a.

Write Enable Assembly.

b.

Density Select Assembly.

c.

Unit Select Assembly.

the tape unit,

mayor

may

not

be a part

1-2

Part 2

7970B/7970C

Theory

of

Operation

SECTION

THEORY

2-1. INTRODUCTION.

2·2. This section provides an overall functional descrip· tion

of

the tape transport and description circuits. Block diagrams are included ing the operation

2-3.

2-4. The tape transport controls the movement netic tape, provides power for read and write

and supplies status signals

mands (High-Speed, Reverse, Forward, Rewind, and Off-

Line) are generated by the interface. The off-line and online commands are processed by the control and status circuits and result in controlling signals for the capstan servo,

reel servo, and front panel indicators are also provided by the control and status circuits. Figure 2-1 of

OVERALL

the tape transport circuits.

of

the transport circuits.

FUNCTIONAL DESCRIPTION.

to

the interface. Off-line com-

and

data circuits. Status signals for the interface

is

a functional block diagram

of

the transport

to

aid in understand-

data

OF

of

mag-

circuits,

II

OPERATION

the

2-9. A Rewind command generated by will initiate the rewind sequence. The control and status circuits place the capstan servo circuits verse mode and switch the reel servo feedback circuits. The capstan rewinds tape with current feedback. When the trailing edge beginning-of-tape status circuits terminate second delay, establish a load

2-10. Pressing RESET releases the tape unit from interface control. Pressing REWIND in this condition rewinds the tape take-up reel, the tension arms switches, the capstan motors are shorted. This provides dynamic braking reel motors.

2-11.

on

the supply reel. When the tape

CIRCUIT

at

160

ips and the reel servo operates

(BOT) tab

motor

is

detected, the control and

the

rewind mode, and after a one-

point

contact

circuit

DESCRIPTIONS.

in

search mode.

the tension arm limit

is

broken and the reel

interface

a high-speed re-

of

is

run-off

of

the

2-5. At initial power-on, the capstan open, and the reel servo motors are shorted. When the LOAD switch are completed. When tape tension arms swing away from the tension limit switches. With tape tensioned, the capstan and reel When the circuits initiate a load the reel servo circuit operates with voltage feedback and the capstan servo pulls tape forward

sense assembly, the control and status circuits terminate the load point search, and tape motion stops. The control and status circuits provide a load and the

control controls have

of

data

voltage feedback and tension of-tape tab vide the interface with an end-of-tape (EOT) status.

is

pressed, the capstan

LOAD switch

point

2-6. When the load

front

panel LOAD indicator illuminates.

2-7. Pressing the ON-LINE switch establishes interface

of

the tape unit. Except for RESET, the front panel

no

control

releases the interface control and allows

the tape unit.

2-8. When the tape unit

is

being processed, the tape unit pulls tape

nous speed

as

required. The reel servo circuits operate with

is

detected, the control and status circuits pro-

motor

is

motor

is

released, the control and status search. During load

at

20

point

tab

is

point

of

the tape unit. Pressing RESET

is

under interface control and

is

maintained. When the end-

motor

circuit

and reel

established, the tension

returns are maintained.

detected by the photo-

status

ips.

motor

to

the interface,

front

panel control

point

at

synchro-

circuits

search,

is

2-12. The following paragraphs describe the power supply circuits, control and status circuits, capstan servo circuits and reel servo circuits of

the circuits are provided operation schematic diagrams

2-13.

2-14. The power supply a power transformer, three center-tapped bridge rectifiers, filter capacitors, and bleeder resistors. primary circuit switch power on-off switch, and a line filter/power connector_ When 115 of vides overload protection. When 230 Vac power the two primary windings series, and fuse F2 ing

2-15. The power distribution circuits are distribution and connectors for power distribution. The assembly also contains a printed-circuit connector for the power regulator printed-circuit assembly. cuits and the ±12 volt distribution circuits provide circuit protection.

of

the circuits. Refer

POWER SUPPLY AND POWER DISTRIBUTION CIRCUITS.

that

allows selection

Vac power

the power transformer are in parallel and fuse F1 pro-

to

provide overload protection.

PCA. The assembly contains secondary fuses

of

the tape transport. Block Diagrams

as

an aid in understanding the

to

section VII for detailed

of

the tape transport.

of

the tape transport consists

(See figure 7 -2.) The

of

the power supply transformer includes a

of

115

or

230 Vac operation, a

is

selected, the

of

the power transformer are

is

placed in series with the primary wind-

Silicon diodes in the ±20 volt cir-

two

primary windings

is

selected,

on

the power

of

in

Part 2

2-1

Theory

of

Operation

SUPPL Y REEL TENSION ARM

TAKEUP TENSION ARM

REEL

SERVO

REEL

CIRCUITS

SUPPLY REEL MOTOR

M

TAKEUP

REEL MOTOR

M

7970B/7970C

bl

7970 508

TENSION

SWITCHES

OFF-LINE COMMANDS (FRONT

PANEL!

STATUS (FRONT

PANEL!

ON-LINE COMMANDS (INTERFACEI

STATUS (INTERFACEI

PHOTOSENSE

ASSEMBLY

t

CONTROL

AND

STATUS

CIRCUITS

BOT/EOT

t

CONTROL

r-~,

I

DATA

CIRCUITS I

(SEE

PARTS I

3,4

I

L

OR

__

Figure 2-1. Tape Transport Functional Block Diagram

51

I

AND

FEEDBACK

STATUS

-.J

CONTROL

MOTION

CONTROL

TENSION/TENSION

LATCH

CAPSTAN

SERVO

CIRCUITS

CAPSTAN MOTOR

M

'1

TACHOMETER I

'-.J

I

1

I

I I

I

·1

I

1

I

I I

Kl

(LOCATED

REEL SERVO

ON

PC

AI

2-16. tributed to

Unregulated power from the power supply

to

the power regulator printed-circuit assembly and

heatsink-mounted power transistors. Unregulated ±40 volts (57.5 volts nominal) from the power supply through heatsink-mounted resistors to the power regulator printed-circuit assembly. Regulated power (+5

-12V) from the regulator-controlled transistors mounted) are distributed

to

the transport circuits and data

circuits by the power distribution printed-circuit assembly.

2-17. the power supply ing diodes CR1 and CR2 allows the switch from 22.5 volts dc

Unregulated ±20 volts (22.5 volts nominal) from

is

provided for the reel servo circuit. Steer-

±20/40

to

57.5 volts dc.

2-2

is

routed

V,

+ 12V, and

(heatsink-

volt lines

is

dis-

2-18.

POWER REGULATOR CIRCUITS.

2-19. The power regulator printed-circuit assembly contains a + and a +5 volt regulator circuit.

12

volt regulator circuit, a

-12

volt regulator circuit,

(See figure 2-2.) The power regulator printed-circuit assembly also contains a reel servo voltage switching circuit and

a delay circuit. These circuits

are described with related circuits.

2-20. +12 VOLT REGULATOR. The +12 volt regulator uses an integrated circuit voltage regulator with an internal

to

temperature compensated voltage reference. Regulation obtained by dividing the

output

voltage (R3,

R4,

is

and R5)

Part 2

7970B/7970C

Theory

of

Operation

TRANSFORMER

ASSEMBLY

+40V (NOM)

-40V

(NOM)

+20V

-20V (NOM)

+12V (NOM)

~&

J

+5

VOLT

REGULATOR

'"'"

~:9

~

~&

/1-

+

-12 VOLT +12

REGULATOR REGULATOR

~

VOLT

REF

~

+40V UNREG

-40V UNREG

+20V UNREG

-20V UNREG

+12V

REG

-12V

REG

+5V

REG

7970·509

Figure 2-2. Power Supply Voltage Regulators, Simplified Diagram

and comparing the divided voltage with the internal refer· ence. The able by variable resistor R4. cated on a heatsink external by current limiting. The current foldback knee

output

voltage

of

the +12 volt regulator

Series pass transistor

of

the regulator)

is

adjust·

Q2

is

protected

is

set

to

(lo-

approximately 2.8 amperes by R1 and R2. Short circuit current

is

set

to

approximately 1.3 amperes by R7 and R8

(located on heatsink external

-12

2-21.

VOLT REGULATOR. The

to

the regulator).

-12

volt regulator uses an integrated circuit voltage regulator. The reference for the

volt source. at

protects the mode voltage. Diode volts in the event that the + 12 volt reference

2-22.

-12

volt regulator

Current limiting

1.2 amperes

+5

VOLT REGULATOR. The

is

derived from the regulated + 12

of

the

-12

volt regulator

as

determined by R9 and R20. Diode CR14

-12

volt regulator against excessive common

CR17 limits the

output

+5

voltage

is

lost.

volt regulator

to

is

set

-14.7

uses an integrated circuit voltage regulator. The reference

+5

for the lator

output

+5

volt regulator

using R23, R25, and R26. Current limit

is

generated from the + 12 volt regu-

is

approximately 4.0 amperes controlled

of

the

by current sense resistor R6, located external

of

lator on a heatsink. In the event controlled rectifier

CR1 conducts and shorts the +5 volt

an over-voltage, silicon

of

the regu-

supply. The 4 ampere short circuit current will blow fuse

is

F5 which

in series with the +10 volt unregulated supply.

2-23. CONTROL AND STATUS CIRCUITS.

2-24. The control and status circuits process commands from the front panel controls and interface and generate controlling signals for the tape transport and data circuits. The control and status circuits also generate status signals for the interface and front panel indicators.

2-25. After power

sioned, limit switch

is

applied, the tape

W2S1

is

open and the capstan and

is

not

ten-

reel servo circuits are disabled (figure 2-3). The capstan and reel servo circuits are disabled because relay

deenergized and because ground voltage is supplied

the Tape Tension signal line through deenergized relay on the control and status output from

the

Kl.

Ground voltage supplied

PCA,

LDFD

FF

to

the

B contacts

results in an inactive

the capstan servo circuit.

to

K1

to of

Q4,

is

Part 2

2-3

Theory

of

Operation

7970B/7970C

Also, ground voltage supplied servo

PCA

holds switch Q20 closed, grounding the input Q2, Q4, and Q6. Ground voltage applied reel servo amplifier

PCA, by the Tape Tension signal and through the normally closed contacts switch, cause it

to

close switches Q16, Q17, and Q20 on the reel servo amplifier reel servo amplifiers grounded, abled. Relay

K1

is

also kept deenergized through the normally closed contacts on

the reel servo amplifier

switch

is

pressed, +5 volts

R103 to activate the Tension signal

the reel servo amplifier

energizes relay K1.

(Once energized,

to

Q22

on

the capstan

on

the capstan servo

to

motor drive amplifiers

to

Q19

of

the LOAD

PCA.

With the inputs

the

reel motors are dis-

of

the LOAD switch and Q13

PCA.

When the LOAD

is

supplied through R9 and

to

Q13 and Q19 on

PCA.

The high input

K1

remains ener-

to

on

to

PCA

the

Q13

gized, through R109, CR11, and Q13, until tension lost.) Pressing the LOAD switch also applies a high

on

input to Q19

gate Q19 holds Q16, Q17, and

inputs are high. With

the reel servo amplifier

Q20 open if either

K1

energized,

both

are high causing switches Q16, Q17, and

reel servo amplifier ments for enabling

PCA

to

open. Thus,

the

reel servos (K1 energized and

PCA.

inputs

Q20

both

Nand

of

its

to

Q19

on

the

require-

switches Q16 and Q17 open) are met and the reel servos tension the tape. Thus, with K1 energized and Q20

on

the reel servo amplifier

PCA

capstan servo capstan servo

(through Q21) opens Q20

PCA

and enables the amplifier. With tape tension established, tension arm switch supplying a high input ward

FF

and

to

Q19

to

the reel servo amplifier

2-26. When the LOAD switch search sequence set. The to signal

output

clock the Load Forward flip-flop (U12A). The LFWD

is

gated with DELAY

is

initiated. Load Latch (U1A and U2A)

of

the load latch

PCA

open, Q22

W2S1

terminal D

to

provide the capstan servo

of

the Load For-

is

released, the load point

is

gated with

REW

on

closes,

PCA.

(false)

the the

with the load point search command.

to

the interface and rewind status

to

assembly

illuminate the REWIND indicator.

2-30. When the trailing edge

of

the load

to

the

tected during rewind the Load Point flip-flop

is

Rewind flip-flop

11). Load point also gates U3B

set through the rewind clock input (U6B-

to

prevent rewind commands from clearing the Rewind flip-flop. With the Rewind flop set, the Load Forward flip-flop This starts the load

point

search mode.

is

set through gate U13A.

2-31. The control and status printed-circuit assembly tains a unit select network

that

allows up

to

controlled by one interface. The network consists

(W1)

is

jumper position the interface.

and 5 connecting pins (OFF, 0,

of

the jumper determines the unit

If

the units connected

to

the interface are equipped with the unit select switch option, the jumper must be in the position the select match circuitry printed-circuit assembly

OFF position. With the jumper in the

of

the control and status

is

disabled.

If

the tape units are equipped with the unit select switch option, the jumper must be connected

to

positions 0 through 3 depending upon

unit designation.

2-32. The unit select command from (CSO,

CS1, CS2 or CS3)

is

gated with ON-LINE

generate SOLA and SOLB (selected and on-line). The

SOLA condition allows status signals

the interface. The SOLB condition

to

is

gated with

(load sequence completed) to generate EXT (external

control). The EXT condition allows interface commands

to

is

be processed. The OFF-LINE command from the

not

interface does LINE command to

clear the On-Line latch (U1D and U2B).

require the EXT condition. The OFF-

is

gated with the unit select command

control switch

point

tab

is

de-

is

set and the

flip-

con-

four units

to

of

1,

2,

3)_

The

be selected by

OFF

not

the

interface

be

supplied

COMP

be a

to

2-27. The DELAY signal

is

generated by a delay circuit located on the power regulator printed-circuit assembly. The delay circuit provides a one-second delay when changing

to

from a high speed operation

a synchronous

search mode.

is

2-28. When the load point tab

is

Load Forward flip-flop

cleared by

detected (BOT), the

LP U13B. Pressing RESET will also clear the Load Forward flip-flop. search motion Load Complete flip-flop

When

will

Load Forward

is

cleared, tape load point

stop. The edge transition

U12B. Except for a rewind condition, Load Complete remains set during normal operation of

the tape transport.

2-29. Rewind flip-flop REWIND switch when the unit face command Rewind flip-flop (U4B and U3A)

REW

is

U6B

is

cleared

is

off-line,

when the unit

is

cleared, the Rewind Status flip-flop

set. This provides rewind status

2-4

or

load point

through U16D and

of

LDFD clocks

by

pressing the

or

by inter-

on-line. When the

SRW

2-33. The Rewind command (REW) from the interface gated with EXT provided and high-speed (FWD, REV and to

provide motion commands

that

to

clear (assert) the Rewind flip-flop (U6B),

tape

is

not

at

load

point. The forward, reverse,

HIGH SPEED) are gated

to

the tape transport servos

and data circuits.

All

2-34.

status signals

SOLA. The load point status (SLP) indicates

is

at

unit

load point (load point tab under photosense head).

The end-of-tape status (SET) indicates

to

the interface are gated with

that

the tape

that

the tape

is

at

beyond the end-of-tape tab. The rewind status (SRW) indi-

cates that the tape

point search operation. The ready status (SR) indicates the tape unit is

complete

is

(not mode). The on-line status (SL) and file protect status indicate

that

stalled on the supply reel hub

is

rewinding

or

in an automatic load

selected, on-line, and that the load sequence

rewinding and

not

in a load point search

(SFP)

the. unit

is

on-line, and that the tape reel

is

not

equipped with a write

that

enable ring.

Part 2

is

or

in-

7970B/7970C

Theory

of

Operation

2,35.

The one-second delay (generated on the power regulator printed-circuit assembly) following a high-speed reverse command prevents additional high speed commands

from being processed by the control and status circuits. The delay also prevents the load point search from occurring for one-second following a rewind operation.

2-36.

CAPSTAN SERVO CIRCUITS.

2-37. The capstan servo circuits control the speed and

direction

The capstan servo consists

and a capstan servo printed-circuit assembly. The servo

of

tape motion across the magnetic head assembly.

of

a capstan motor/tachometer

cir-

cuit employs current and velocity feedback. The velocity

is

feedback

ometer attached to the capstan

back

is

motor

provided by the magnetic moving coil tach-

motor

shaft. Current feed-

provided by a pair

return circuit. Figure

of

sensing resistors in the capstan

2-4

is

a block diagram

of

the

capstan servo circuit.

2-38. Motion commands from the control and status printed-circuit assembly control switching circuits and a polar ramp generator. The

output

of

the ramp generator

bi-

and high-speed control signals control the capstan closedloop servo amplifier. The capstan servo amplifier consists

of an integrated circuit servo preamplifier (U4) and a capstan power amplifier

(Ql

through Q6).

2-39. The forward and reverse switching circuits contain temperature compensated zener diodes

that

provide a basic reference voltage for forward and reverse speeds. When a FWD

command from the control and status circuits service switch verse biased. Bias current for CR6

R33

to

(U2 and U3). A REV command

switch

in

S2

is

placed in the on position (up),

is

then provided through

establish a

the

-6.2

volt reference for the ramp generator

or

placing the REV service

on position (up) will provide bias current for

of

Q7

FWD

is

re-

CR2 through R27. CR2 will provide a +6.2 volt reference

for the ramp generator. The forward and reverse reference voltages to

at

the

output

control the forward

of

U3

are independently adjustable

or

reverse speeds.

HSFWD------~----------------~_:~::~

LPSEARCH-----------------+~----~

TENSION

----------------4~

7970511A

'-

....

--------------------------------------------------------------_

HSFWD

L---o-~

.12V

12V

OFFSET

TENSION

TO

REE L

cCA

SE

RVO

Part 2

Figure 2-4. Capstan Servo, Block Diagram

2-7

Theory

2-40.

of

Operation

The bi-polar ramp generator consists grated circuit operational amplifiers cal 8-volt clipping network ramp control network

(CR7 through CR11), and a

(R42/C28).

of

two inte-

(U2 and U3), a symetri-

is

10

volts

per

volt determined by RIO and R11. The power

amplifier

is

operated in class B with Q6 providing negative

current for forward motion and

rent

for reverse motion.

7970B/7970C

Q5

providing positive cur-

2-41. Operational amplifier saturating is

given

down

comparator

or

removed. Near the end

U2

changes from a saturating comparator

when a forward

amplifier with the non-inverting input

2-42. The clipping network

output

of

U2

(CR7 through CR11) which establishes current for the ramp control network. The slope ramp

is

determined by the current through R42 (RAMP

is

U2

initially operates

of

at

held

to

8 volts by a symetrical

or

reverse command

a ramp-up

or

to

a linear

O-volts.

as

ramp-

of

the

control) into integrating capacitor C28. Feedback through

R66 nulls the reference input voltage

voltage

of

the ramp generator (U3-6)

ratio determined by R66 (R35 + R34)

2-43. When the Forward or Reverse command the current through R66 drives operational amplifier to

saturation and the ramp integrates the 0 volts.

output

of

the ramp generator (U3-6) approaches 0 volts, reverts generator

to

a linear amplifier and the

is

maintained

at

0 volts.

to

U2

and the

is

held steady by the

or

R66 (R29 + R28).

output

is

removed,

As

output

of

the ramp

U2

in-

the

U2

2-44. A High-Speed Forward command (HSFWD) from the control and status circuits or placing the + switch in the on position (up) will allow conduct is of

and reverse bias Q8. With Q8 reverse biased, C25

charged through R49. The exponential voltage at the base

Q9 rises

to

+ 12 volts

but

is clipped at +6 volts when Q9

CR12 and CR13

saturates. When the HSFWD command +160 service switch

is

placed in the

off

U1B conducts placing U1B-4, CR12, and CR13 This allows Q8

to

conduct and C25 discharges through R48.

The threshold caused by the base emitter turn-on voltage

Q9

and the diode drop across CR14 results in a delay

approximately 100 ms before motion starts

2-45. A High-Speed Reverse command (HSREV)

ing the

-160

service switch

the high-speed reverse ramp circuit

in

the

on

position, (up) will cause

to

function the same the high-speed forward ramp circuit, except polarities are reversed. Capacitor

C26

is

160 service

is

removed

or

position (down),

at

0 volts.

or

stops.

or

plac-

that

voltage

charged through

to

the

of of

as

R56 and discharged through R54 and R55.

2-46. The circuits does the capstan servo amplifier resulting in a nominal

2-47. The

LOAD command from the control and status

not

control a ramp circuit. The load switch

is

a single step input

to

the capstan servo

of

20 ips tape motion.

outputs

of

the bi-polar ramp generator, highspeed forward ramp generator, high-speed reverse ramp generator and load switch form a summing junction at the input of

the capstan servo preamplifier (U4). Diodes CR17 and CR18 provide clipping load. The preamplifier drives the capstan plifier (Q1 through Q6). The dc gain

to

protect

the amplifier from over-

motor

power am-

of

the power amplifier

a

2-48. A

the tachometer

sponse

notch

filter in the velocity feedback circuit from

is

selected

of

the motor-tachometer combination. A compensat-

to

attenuate

the mechanical re-

ing network in the current feedback circuit depending upon synchronous speed

of

the tape unit.

2-49. Transistor switch Q22 senses the presence tape tension. While the tape is tensioned, Q22 is on,

keeping switch

Q22 turns off, allowing

input

of

Q20 off. However, when tension is lost

Q20

to

turn

on

motor

drive amplifiers Q2, Q4, and Q6

ground. This disables the capstan servo. The capstan

motor relay energized. Relay button

circuit

K1

is

completed through

on

the reel servo amplifier

K1

is energized when the LOAD push-

is pressed. Once energized,

the

PCA

it

remains energized

until tension is removed.

2-50. REEL SERVO CIRCUITS.

2-51. The reel servo circuits consist

of

a tension circuit, a voltage switching circuit, a delay circuit, voltage/current feedback switches, tension arm photosense circuits, preamplifiers, is

motor

power amplifiers, and reel motors. Figure 2-5

a block diagram

of

the reel servo circuit.

2-52. At initial power-on, the tension circuit The normally closed contacts prevent Q13 the

LOAD control allows Q13

K1. With

of

the tension circuit from conducting. Pressing

K1

energized, the capstan and reel servo

circuits are completed.

As

of

tape

LOAD

to

is

pushbutton

conduct, energizing relay

tensioned and the tension

arms swing away from the limit switches, power through the

limit switches maintain a forward bias

is

removed,

across the reel

or

tape tension

motor

is

windings

lost, the relay contacts short to

2-53. The voltage switching circuit

of

Q13. When power

provide dynamic breaking.

is power regulator printed-circuit assembly. During a highspeed operation forward or reverse, power power amplifiers

is

switched from 22.5 volts

(nominal).

2-54. During a high-speed reverse operation (rewind), the HSREV command from the control and status circuits

gated with TENSION. When r/min, the

motor

voltage exceeds the break-down voltage

both

reel motors approach full

CR4. The condition established by the gating and Tension allows current through Q5. Voltage switch the

+20/40 printed-circuit assembly volts from entering the

Q6/Q7

conducts placing +57.5 volts on

line. Diode CR2

is

back-biased preventing +57.5

+20 volts line.

CR4

on

the power distribution

is

also selected

of

and switch the

to

B contacts

when

is

of

K1

is

disabled.

switch

motor

located

to

the

to

57.5 volts

on

the

motor

is

of

HSREV

to

forward bias

2-8

Part 2

7970B/7970C

+SV

~~~~-4~~~~~~~~~~~AI

Theory

KIA

(ENERGIZED)

).

of

Operation

I

L

+20V

------------iM-----

-----------t4----i>---+---,--II

-20V

HSFWD

__

_

R26

...

---+-..

">cHI-_

-20/40V

R27

+20/40V

..

-20/40V

MOTOR VOLTAGE

DELAY CONTROL STATUSPCA

FEEDBACK CONTROL

TO

AND

R47

VOLTAGE FEEDBACK

SUPPLY REEL MOTOR

-SV

7970-512

Part 2

VOLTAGE

>-

.... -__

-20/40V

RB

R7

-<11-

____

Figure 2-5. Reel Servo, Block Diagram

RIOS FEEDBACK

-----------

...

I

.J..

KIC

TAKEUP

REEL

MOTOR

(ENERGIZED)

2·9

Theory

2-55. During a high-speed forward operation, the voltage switching circuits function the same operation. voltage

of

Operation

HSFWD

to

switch the

is

gated with tension

-40

volt switch

as

in the fast reverse

to

allow

(QI2/QI3).

motor

7970B/7970C

C8

is

then charged through R33 (one-second time constant).

is

When C8 feedback control changes from switches

charged

to

0 volts.

to

+5V, Q16 and Q18

-8V

conduct

to

+8V. The DELAY

and the

2-56. The delay circuit printed-circuit assembly. The delay circuit provides an tional one-second delay following the end command. The one-second delay prevents further high-speed commands from the interface from being processed during the one-second period. The one-second delay switch the reel servo operating mode from voltage feedback to

current feedback. The additional one-second following a high speed operation allows the reel servo current feedback mode until reels are slowed.

2-57. During normal operation, U5A-3 and U5B-4 rest

o volts. A HSFWD

and status circuits will cut-off U5A for Q15 ducts, capacitor C8 immediately discharges through Q15 causing Q16 and Q18 reel servo changes from approximately +8 volts mately Q17 and the DELAY line switches

2-58. When the high-speed command HSREV)

is

supplied through R28

-8

volts. The negative potential also reverse biases

is

removed and Q15 loses base current, capacitor

is

located on the power regulator

of

a high-speed

is

also used

to

operate in a

or

HSREV command from the control

or

U5B

and base current

or

R29. When Q15 con-

to

be cut-off. Feedback control

to

approxi-

to

+5

volts.

(HSFWD

addi-

to

at

the

or

2-59. The reel servo tension arm assemblies contain dual

that

element photo-conductors shining through a slotted disc. The slot

spiral attached slot exposes different areas result, the to

the position

2-60. The reel servo preamplifier tional amplifier sion arm. The tension arm photo-conductor ended, therefore, an off-set The preamplifier drives a class B The

motor

2-61. When operating in a normal mode (synchronous or

load speed), the servo operates with voltage feedback.

The +8 volts from the feedback switching network back control) back-biases the feedback FET switch (Q14 and

QI5).

RI05.

During a high-speed operation, the feedback control changes biased and feedback

to

the tension arm.

output

to

of

the photo-conductor

of

the tension arm.

that

amplifies the position

power amplifier has a gain

Feedback

-8

is

volts. The feedback FET switch

is

current through the switch.

are illuminated by a lamp

is

in

the

form

of

As

the arm moves, the

of

the photo-conductor.

is

proportional

is

an integrated opera-

error

output

is

provided by R39

motor

then provided through R47 and

drive amplifier.

of

10 volts

of

the ten-

is

or

per

is

forward

As

single-

R41.

volt.

(feed-

a

2-10

Part 2

7970B/7970C

Performance Checkout

SECTION

PERFORMANCE

3-1.

3-2. This section provides checkout instructions ify specifications. The test procedure assumes ing general conditions apply structions

3-3. TEST EQUIPMENT REQUI RED.

3-4. For the purpose that computer the ing instructions for the equipment tation applicable

3-5. available all adjustments. Computer operation following electronic test instruments (or equivalent) are also required:

Generator.

meter Plug-In.

3·6.

port

various signals for accurate speed measurements

3-7. CHECKOUT PROCEDURES.

3-8. Performance checkout procedures for the tape unit consist of:

I NTRODUCTI ON.

that

the tape unit conforms

to

the contrary are stated as part

the person conducting

or

an off-line test set

following requirements.

to

the

equipment.

a.

Provides all standard functional commands.

b. Responds

An

as

a.

HP

b.

c.

HP

In addition

test tape

a.

Preliminary Power-Off Checks. Operator Control Checks.

b.

to

all status outputs.

HP

13191A Control and Status Test Board

a service accessory and will meet the needs for

140A Oscilloscope with

1421A Dual-Trace Preamplifier (for

5245L Counter with

to

the listed test equipment, a trans-

HP

part number 5080-4525

to

published performance

at

all times unless specific

of

this procedure,

the

test will be using either a

that

is

It

is

also presumed

is

provided by documen-

is

HP

5265A Digital Volt-

to

that

the follow-

of

a test routine.

it

is

presumed

capable

of

meeting

that

operat-

also suitable. The

1421A

that

Time

HP

140A).

generates

is

required.

Base

ver-

in-

III

CHECKOUT

c.

Service Switches and Accessory Checks.

d. Tape

e.

f.

g.

3-9.

3-10. Preliminary power-off checks are performed follows:

a.

and have no end play.

b.

should operate freely and should have clearance between

of

face ness without binding).

is

c. Tension Arm Limit Switches: The three limit switches associated with the tension arms must operate when the arm stop. The roller on the switch arm should be approximately on the center stop. There should be positive travel yond

the check can or

with an ohmmeter if room noise

d. finger nominal location dimensions should be

Path Evaluation.

Power Supply Voltage Checks.

Tape Speed and Capstan Servo Checks.

Transport Function, Motion, and Status Checks.

PRELIMINARY POWER-OFF CHECKS.

Tape Rollers: The tape rollers must operate freely

Head Crosstalk Shield: The head crosstalk shield

head and shield (room

is

approximately 1/8 inch from the rubber

of

the arm when the arm

point

at

which it actuates the microswitch. The

be

made audibly if ambient noise level permits,

Write Enable Sensing: The write enable sensing

(1) The distance between the outside surface

the write enable sensing finger and the outside flange diameter should be 3/32-inch (nominal).

(2) In the file protected position (inoperative),

the dimension between the sensing finger and the turntable should be 3/16-inch (nominal) above the turntable surface.

(3) In the write enable position (with solenoid

energized) the should be 1/16-inch below the turntable surface.

(4) The sensing finger must

table under any condition.

to

slip a punched card thick-

is

fully against

of

the switch lever be-

is

too

high.

as

of

the reel turntable

outer

face

of

outer

tip

of

the sensing finger

not

touch the turn-

follows:

tip

of

the reel

the

as

of

the

Part 2

3-1

Performance Checkout

7970B/7970C

e. Reel Retaining Knob: With the locking lever

re-

leased, the reel should slip over the rubber grip ring easily,

and it should be possible lever

is

closed, positive resistance should be felt

ber

is

compressed. In the locked position, possible place a piece the should hours

to

move the reel by hand.

of

masking tape

hUb.

A mark placed in alignment on

not

become misaligned by more

of

operation. To correct tape reel slippage, release locking lever and loosen the pozidrive screw, retainer

knob

clockwise, and tighten the screw. Repeat until

tape reel mounts firmly and does

3-11.

OPERATOR CONTROL CHECKS.

3-12. Verify position connect unit

to

appropriate power source and check the

to

easily rotate the reel. When the

as

the rub-

it

should

If

of

115/230

slippage

on

the reel, and another on

not

slip.

volt selector switch;

both

than

is

suspected,

pieces

of

1/8 inch in

rotate

the reel

not

be

tape

16

following operating modes.

3-13. reel the power switch on. After threading tape, press verify

TAPE LOADING AND WRITE ENABLE. Place a

of

tape (with write enable ring) on unit and thread with

LOAD and

that

the following takes place.

a.

Tape tension

is

established. RESET indicator

il-

luminates.

the load command and will return the tape to the position (LOAD indicator may be terminated prior Transfer

to

on-line

on

with tape stopped). Rewind

to

load

point

by pressing RESET.

is

also possible immediately following

load

point

this sequence.

3-17. SERVICE SWITCHES AND

ACCESSORY

CHECKS.

in

3-18. There are three service switches incorporated

the capstan servo card. These together with the REWIND and LOAD controls provide a means modes for service and

lor adjustment purposes. There

of

operating all five drive

is

no

capability for cyclic drive operation.

HP

3-19. The

13191A available for use with the tape unit. With this test board is

possible

of

the control and status function

to

completely adjust and verify the performance

Control and Status

of

a tape unit

Test

Board

under

is it

offline conditions. Complete operating details are included with the test board. The Board provides normal drive modes gramming which

HP 13191A Control and Status Test

as

well

as

cyclic pro-

is

suitable for adjustment

of

the capstan start/stop ramp. The board also includes status indicator lamps

to

verify all normal status functions. The test board

is

installed in the connector

status

PCA.

of

the tape unit control and

b.

WRITE ENABLE indicator illuminates.

20 ips

to

load

point

c. Tape moves forward at

tab

(BOT tab).

d.

LOAD indicator illuminates.

3-14.

control and status

OFF and load tape. Following completion with tape positioned

press

commands.

process will also result in

pleting the search (LOAD indicator

the unit will

tion

3-15. DYNAMIC BRAKING AND

POWER

well

turn

stop

ON-LINE TRANSFER AND RESET. Place the

PC

assembly unit select jumper

pin (this

ON-LINE and verify

is

not

the same

at

as

OFF

on unit select option)

of

a load sequence

load point (LOAD indicator on),

that

unit will respond

to

Pressing ON-LINE while load point search

ON-LINE operation upon com-

is

ON). While ON-LINE,

not

of

RESET.

respond

to

local controls with the excep-

RECOVERY FROM

FAILURE. Place unit in rewind mode after tape

into

take-up reel. When full rewind speed

power switch

without

off

to

any damage

simulate power failure. Tape should

to

tape. Proceed with recovery

is

in

the

external

is

in

reached,

to on-line status by following normal load sequence. Except that

when tape unit goes into the load

load

point

tab may be simulated by pressing the RESET

button.

3-16. REWIND

This can then be followed by an on-line command.

OPERATION. The REWIND control

operational only while the unit

point

search mode,

is

in the reset state which

permits local control. The rewind command will override

3-20. TAPE PATH

3-21. With undamaged tape threaded

EVALUATION.

on and with the unit in the appropriate operating mode, ate the following characteristics

a.

Capstan Height: Capstan height should be such the tape edge

is

guided equal distance in from the

of

the capstan. The air escape grooves provide a means

of

the tape path.

for judging.

b.

Tension Position: Arms should be aligned with the centering marks on the rear ceptable provided the arm than the diameter

of

the arm.

c. Tape Tracking

of

the casting. Position

is

not

out

of

location by more

Over the Tape Guides: Tracking over the guides should be smooth with no evidence forces anywhere in the tape path. Transverse reflected light may be used

is

the 1/2-inch width points

d. sembly should be parallel tioned

3-22.

to

assist in judging. Light reflections across

of

the tape should

of

stress.

Photosense Position: Face

to

the path

1/8

inch from the tape.

not

of

photosense head

of

the tape and posi-

POWER SUPPLY VOLTAGE CHECKS.

is

3-23. Both regulated and unregulated supplies should be

checked for the following specifications.

the

outer

be

bent

tape unit

evalu-

that

and inner

is

ac-

of

edge

due

to

as-

3-2

Part 2

7970B/7970C

3-24. REGULATED SUPPLY VOLTAGES. Regulated

voltages will remain within tolerances over a primary voltage

of

range as

±10 percent.

specified below. The peak-to-peak ripple values are nom-

inal and minor variances may be expected. Ripple

DC

voltages and tolerances are

is

stated

to

be

under tension-only conditions.

+5

a. The

volt supply must be +5.000 ± 0.050 Vdc.

b. The ±12 volt supplies must be 12.000 ± 0.360 Vdc.

3-25. UNREGULATED SUPPLY VOLTAGES. Unregu-

lated supply voltages are a direct function

The following table only at a line voltage nominal and apply at

a.

±40 Vdc: Nominal value

150 mv

POp

(sawtooth).

of

nominal values should be judged

of

115 volts.

60

Hz.

is

of

line voltage.

RMS

ripple values are

±57.5 volts; ripple

of

Performance Checkout

that

the

output

of

For

the follow-

the read HP

part

bit-to-bit distances be read, and preamplifier be connected number accurately spaced

50S0-4525 Transport Test Tape provides frequencies

to

better

to

than

a suitable counter.

0.1 percent. ing tests reference frequencies are based on using the signal that

will

be avail abel from the channel 3 preamplifier track units and channel 6 preamplifier This has a bit-to-bit spacing duce a frequency

of

speed

30.000 ips. Frequencies for

direct ratio

of

10,000

to

the change in speed relation to 30 ips. Ex-

of

Hz

of

0.00150 inch when reproduced at a tape

other

ample: 60 ips would produce 20,000 Hz.

seven-track units.

Use

of

nine-

and

will pro-

speeds are in

this principle

and check the following:

a. High-Speed Forward:

53,333

Hz.

160

ips, basic frequency

(1) Maximum acceptable operating limit: ±1050

Hz

(±2 percent).

(2) Adjustment recommended if greater than:

±SOO

Hz

(±1.5 percent).

is

+20 Vdc: Nominal value

b.

600

mv

Pop

(sawtooth).

c.

-20

Vdc: Nominal values

300 mv

900 mv

3-26. TAPE SPEED

Pop

(sawtooth).

+10 Vdc: Nominal value

d.

POp

(sawtooth).

AND

3-27. The tape speed and capstan servo checks consist

measuring capstan

motor

offset current, measuring long term

speed variation (tape units capable

is

+22.5 volts; ripple

is

-22.5 volts; ripple

is

+12 volts; ripple of

of

CAPSTAN SERVO CHECKS.

of

reading data), measur-

of

ing start and stop time and distance, measuring instantaneous speed variations, and measuring fast forward, reverse, start

is

and stop. Included

a dynamic tape skew check for tape

units equipped with read and write electronic circuits.

3-2S. CAPSTAN MOTOR OFFSET CURRENT. Connect

or

a suitable dc voltmeter percent resistor (R21 tors

is

sion

connected

but

no tape motion, the voltage should

to

following referenced

a.

Maximum acceptable operating limit: ±100 mv

oscilloscope across the 3 ohm 1

or

R22). The return side

pin 2

of

CJ-1. With the tape under ten-

not

to

0 V dc.

of

the resis-

exceed the

dc

at 25°C.

b. Adjustment recommended if greater than:

±SO

mv

dc.

3-29. tape speed accuracy over any interval greater than one ond and under each of

LONG TERM SPEED VARIATION. Measure the

of

the

five

drive speeds. The principle

measurement requires

that

a tape having highly accurate

sec-

b. Rewind (High-Speed Reverse): Checked identically

to

the limits applicable

the rewind mode

is

to

high-speed forward, except

used.

that

c. Forward and Reverse Drive: Frequency depends

other

on tape speed and must be calculated for speeds

than

25 ips and 37.5 ips which are tabulated below. Maximum

is

acceptable operating limit justment recommended if speed error

based on ±1 percent with ad-

is

+O.S

percent

or

greater.

is

(1) The 25 ips drive nominal frequency

Hz.

Acceptable limits are ±S3 Hz; adjustment

is

required if greater than ±65 Hz.

(2) The 37.5 ips drive nominal frequency

S,333

is 12,500 Hz. Acceptable limits are ±125 Hz; adjustment

is

recommended if greater than

±100 Hz.

d. Load Point Search:

6,667

Hz.

(1) Maximum acceptable limit

20 ips; basic frequency

is

±1330

Hz

(±20

is

percent).

(2) No adjustment

3-30.

START

MEASUREMENT. Start measurements (both forward and reverse) are made ment of the characteristics defined requires unit be driven with commands greater than the specified start/stop times and

is

provided.

that

are adjustable

as

follows. Measure-

that

the tape

to

that

there be

periods

a provision to synchronize an oscilloscope sweep directly

to

from these commands (both start and stop). The tape

be read may be any previously recorded tape, preferably at SOO

cpi,

as

this provides the best resolution where measure-

ments from preamplifier

outputs

are required. Wavelength

Part 2

3-3

Performance Checkout

7970B/7970C

accuracy

is

not

a factor in this test. Do

not

make measure-

ments during read-after write operation.

Note

The definitions apply for both forward and

reverse directions. The capstan tachometer voltage will reverse polarity when direction

is

changed; however, there will be no observable difference in the preamplifier

a.

Start-Ramp Delay Time: The time (following a start

command) required for the capstan tachometer voltage

reach a value

cent

of

tion

is

b.

that

the value reached at normal drive speed. Specifica-

0.5 ± 0.5 ms.

Start-Ramp 100 Percent Time: The time (following a start command) required for the analog preamplifier track

output

is

greater than a Vdc

to

first reach

waveforms.

100

but

percent

less than 3 per-

output

of

any

of

the peak-to-

to

peak (or O-to-peak) value established while reading an all "1

's"

tape under steady state drive conditions. This

function

of

tape speed; the following limits apply with the

is

capstan ramp adjustment being made during the forward start mode only.

(1) The 25 ips start-ramp

should be 14.5 ±

100 percent time

0.2 ms for forward ramp,

±0.3 ms for reverse ramp.

(2) The 37.5 ips start-ramp

should be 9.5 ±

0.2

100 percent time

ms

for forward ramp,

±0.3 ms for reverse ramp.

b. Start Balance Time: This

tween the start-ramp

100

is

the time difference be-

percent time and start time for the tape speed involved. This period is

allowed

the time delay

to

provide a balance in tape distance

at

full drive speed represented by the stop-

ramp delay time.

c.

One-half

of

the start-ramp time plus ance time (both in milliseconds) multiplied by in

inches per second equals the start distance (in inches x

3

10-

).

Specifications 0.187 ± 0.020 inch.

3-32. forward and reverse) are made

command) required for the analog fier than established ing in all

a

STOP MEASUREMENT. Stop measurements

as

follows:

a.

Stop-Ramp Delay Time: The time (following a

output

of

to

fall

to

a peak-to-peak (or O-to-peak) value

100

percent

"l's"

b. Stop-Ramp

but

greater than 97 percent

under

steady-state drive conditions while read-

tape. Specification

is

0.5 ± 0.5 ms.

100 Percent Time: The time (following a stop command) required for the capstan tachometer voltage speed value and speed and must

to

reach a level between 3 percent

a Vdc. Specification

not

exceed a time

is

a function

that

of

is

less than the specified stop time for the tape speed involved.

3-33.

STOP DISTANCE. Stop distance

is

follows:

a.

Determine stop-ramp delay time.

the

specified

of

as

it offsets

the

start

the

tape speed

(both

any preampli-

that

is

of

the value

normal drive

of

at

least 0.2 ms

calculated

time

bal-

stop

less

tape

as

3-31. as quires adjustable times and

START DISTANCE. Start distance

follows. Measurement

that

the tape unit be driven with commands

to

periods greater than the specified start/stop

that

there be a provision to synchronize an oscil-

of

the characteristics defined re-

is

calculated

that

are

loscope directly from these commands (both start and stop).

The tape

preferably

where measurements fram preamplifier

Wavelength accuracy

to

be read may be any previously recorded tape,

at

800 cpi

as

this provides the best resolution

outputs

is

not

a factor in this test. Do

are required.

not

make measurements during the read-after-write operation.

Note

The definitions apply for

both

forward and reverse directions. The capstan tachometer voltage will reverse polarity when direction

is

changed; however, there will be no observable difference in the preamplifier

a.

Start-Ramp Time: This

celerate the tape from zero ips

output

waveforms.

is

the time required

to

the drive speed.

It

to

is

ac-

determined by subtracting the start delay time (measured) from the start-ramp

100 percent time (also measured).

3-4

b. Determine Stop-Ramp Time: This quired speed.

to

decelerate the tape

It

is

determined by subtracting the stop-ramp delay

to

time (measured) from the stop-ramp

zero ips from the drive

100 percent time (also

is

the time re-

measured).

c. The stop-ramp delay time plus one-half the ramp time speed in inches inches x

3-34. taneous speed variation departure speed. Measurement

wind of

tape.

fier

output,

(both

in milliseconds) multiplied by the tape

per

second equals the stop distance (in

Specification

is

0.187 ±0.020 inch.

10-

3

).

INSTANTANEOUS SPEED VARIATION. Instan-

is

a measurement

of

the tape velocity from its long

is

made

a.

Write a length

as

reqUired

of

to

be in position

all

b. Connect oscilloscope

position so

that

as

follows:

"l's"

to

any convenient preampli-

waveform

of

the short

term

tape

at

800 cpi and

reproduce this section

is

centered and adjust main sweep sync for positive slope and at

the zero crossover.

average

on

screen,

to

stop

term

re-

trigger

Part 2

7970B/7970C

c.

Use

the delayed sweep feature

to

position the de-

layed sweep at the next zero axis crossover (this corresponds

to

one bit-to-bit distance) with the delayed sweep

auto

trig-

gered from a main (delaying) sweep.

d. Adjust delayed sweep rate

tion

of

the

time shift band

at

to

permit good resolu-

the zero axis crossover. During this evaluation the vertical gain and the delaying sweep time may be adjusted point

is

being observed, it will be the waveform

ing from

top

left

optimize the resolution.

of

screen to

bottom

If

the correct

that

is

com-

right with the slope

to

depending on the gain and delayed sweep speed.

e. Observe the jitter band under conditions in step

"d"

in microseconds peak-to-peak time displacement and

to

multiply by tape speed inches. This value must which are based

(1)

on

±3 percent instantaneous speed variation:

800 cpi must

determine this distance in micro-

not

exceed the following limits

not

exceed ±37.5 micro inches

(75 microinches peak-to-peak).

not

(2) 556 cpi must

exceed ±54 microinches

(108 microinches peak-to-peak).

as

high

Checkout

as

pos-

Performance

peak-to-peak. Again gains must be adjusted sible (both the same) and the delayed sweep trigger set for maximum stability

of

the stable waveform. There will be a

considerable dead zone in the delaying sweep adjustment.

Use

the first operating position from minimum delay position. There the time differential between the stable and unstable

forms. This does

is

a function

not

represent static skew. The difference

of

oscilloscope gain and position settings.

e. Measure the peak-to-peak time band

waveform

as

it crosses the zero axis. Convert this

as

the sweep

is

moved

is

no significance to

of

the unstable

to

micro-

out

wave-

inches peak-to-peak for the tape speed involved. Worst case must

not

exceed ±50 microinches (100 micro inches peak-

to-peak) and applies

3-36. FAST

to

forward

or

reverse mode.

FORWARD/REVERSE

START/STOP CHARACTERISTIC. Fast forward and fast reverse characteristics are measured by synchronizing an oscilloscope with the appropriate drive command, and observing the dc put

of

the tachometer using the TACH test

point

out-

on the

capstan servo printed-circuit assembly.

(3)

200 cpi must

not

exceed ±150 microinches

(300 microinches peak-to-peak).

Note

The above values apply

to

both

the forward and

reverse modes.

3-35. DYNAMIC TAPE that

variation in tape velocity which generates a differential

SKEW.

Dynamic tape skew

time position between the two outermost tracks on the tape. Measurement

a.

to

reproduce this section

b. plifier Use

chopped mode (triggered by channel

sweep synchronized for positive slope triggered

is

made

as

follows:

Write a length

Use

dual-trace oscilloscope and connect

output

of

all

"l's"

of

tape.

the

two outside tracks (channels 4 and 5).

tape. Rewind

A)

with the main

as

required

to

at

zero axis

pream-

crossover. (Use negative slope in reverse direction.)

c. Adjust impose

the varying degrees acteristics

d.

Use

(one bit-to-bit distance later) zero axis crossover

layed sweep. The delayed sweep must be

triggered on the negative slope. (Use positive slope in verse direction.) The earliest delayed sweep and the jitter

that

both

channel gains and positions

to

super-

two waveforms (amplitude only; there will be

of

time difference due

to

static skew char-

).

the delayed sweep feature

of

the two tracks will sync the

other

will arrive later and will have

to

present the next

on

internal sync,

the de-

represents the time differential in microseconds

reo

CAUTION

Do

not

issue sequential fast drive commands without allowing time to reach full speed return to zero speed. Failure caution may cause excessive power dissipation in the reel servo amplifier circuitry. Minimum time between commands should be 1 second the sum is

greater).

of

the start and stop times (whichever

is

3-37. Fast forward/reverse start ured by observing the time (following a start mand) required for the tachometer its maximum value (for start time) stop time). Nominal times are from 400 Typically,

the

value will be 600 milliseconds.

3-38. Fast forward/reverse start termined by the time required for the ramp

to

one state seconds. One-half

the other. This time

of

this time multiplied by

the nominal start/stop distance

3-39.

TRANSPORT FUNCTION, MOTION, AND STATUS CHECKS.

3-40.

The following checks cover the

status and motion command connector.

to

off-line test equipment

verify proper performance

dicated.

3-41. trol and status to

FUNCTION COMMANDS. Select,

PC

assembly includes a jumper

establish

unit

identification where the front panel select

to

observe this pre-

or

stop times are meas-

output

or

to

fall

to

700 milliseconds.

or

stop distances are de-

is

nominally 500 milli-

of

40

inches.

1/0

Use

or

to

or

stop com-

to

either reach to

zero (for

to

move from

160

ips equals

lines in the

appropriate

CS:

The con-

that

can serve

as

in-

Part 2

3-5

Performance Checkout

7970Bj7970C

option jumper can be placed in the response with load sequence completed, the following conditions

to

responding

is

not

present.

to

controller commands, when unit

a.

Unit responds

OFF.

b. Unit responds

CSO

If

no select function

to

commands with jumper connected

to

0 through 3 positions when cor-

through CS3

is

desired, the

off

position which will permit

is

in on-line

and

is

not

rewinding. Verify

check the select (CS) line:

is

selected by the controlling

device.

c. When front panel select option internal jumper in the to

push buttons 0 through 3 When the front panel not

respond

to

3-42. Verify

off

position and verify

is

same

OFF pushbutton

any commands from the controlling device.

that

the off-line (CL) line clears the write

condition and returns the selected tape unit

is

included, place

that

response

as

in step

is

"b"

pressed, unit must

to

the reset

above.

condition.

3-43.

MOTION COMMANDS. Verify

that

the following external commands will place the selected and on-line tape unit in the corresponding drive mode:

a.

Forward (CF): Tape drives forward.

b. Reverse (CR): Tape drives reverse

then

stops

at

load point tab.

CAUTION

Do

not

issue sequential fast drive commands without return

allowing time

to

zero speed. Failure

to

reach full speed

to

observe this pre-

or

to

caution may cause excessive power dissipation in the reel servo amplifier circuitry. Minimum time between commands should be 1 second or the sum is

3-44.

status

outputs

ready tape unit

a.

of

the start and

stop

times (whichever

greater).

STATUS OUTPUTS. Verify

that

the following

are true (low assertion) when a selected and

is

in the condition indicated.

On-Line (SL): True when selected tape unit has

been manually placed on-line.

b. Ready (SR): True when selected

tape loading cycle

is

completed, and tape unit

unit

is

on-line,

not

in

re-

wind mode.

c. Load Point (SLP): True when selected tape unit

has tape positioned

d.

Density (SD2, SD5,

at

the load

point

reflective strip.

or

SDS): Verify

that

selected

tape unit will display the density selected by the tape unit

density switch if this option

the tape unit will be set

is

present. Without this option,

at

SOO

cpi

but

there will be no

SDS

output.

e. Rewind (SRW): Verify

true

as

long

as

the selected unit

Must remain true until tape

that

is

repositioned

this status remains

in the rewind mode.

at

load point

tab.

c. Rewind (CRW): Tape unit enters rewind mode,

mains on-line.

d. High Speed (CH): Tape unit will respond only when

this

is

combined with either a forward

When so combined, tape will drive

at

or

reverse command.

160

ips speed.

CR will drive reverse past load point.

3-6

CH

re-

with

f.

File Protect (SFP): True when selected unit

is

write-enabled.

g.

End-of-Tape (EOT): True when selected unit has

moved end-of-tape tab

beyond

photosense head.

Will main true until tab again passes photosense head in the verse direction.

Part 2

not

rere-

7970B/7970C Repair and Replacement

SECTION

REPAIR

4-1. INTRODUCTION.

4-2. This section provides repair and replacement procedures for the tape transport ital Magnetic Tape Units.

4-3. REPAIR.

4-4. The etched printed-circuit assemblies (PCA's) used are

of

the plated-through type consisting

to

both

sides

of

an insulating material. The metallic conductors are extended through the component holes by a plating process. of

the

PCA mended tools and materials for use in repairing etched The following are recommendations and precautions pertin-

to

PCA

ent

Soldering can be performed on either side

with equally good results. Table 4-1 lists recom-

repair work.

of

the

HP

7970B/7970C

of

Table 4-1. Printed-Circuit Assembly Repair Equipment

AND

Dig-

metal bonded

PCA's.

IV

REPLACEMENT

a. Avoid unnecessary component substitution; it can result in damage components.

b.

Do

heat may lift a conductor

Do

not

or twist drill

may damage the plated-through conductor.

c.

Use

pick

to

remove solder from component mounting holes.

d. After soldering, remove excess flux from the solder areas and apply a protective coating tion and corrosion.

to

the

PCA

not

use a high·power soldering iron. Excessive

or

CAUTION

use a sharp metal object such

to

remove solder. Sharp objects

a suction device (table 4-1)

circuit board and/or adjacent

damage the board.

as

an

awl

or

wooden tooth-

to

prevent contamina-

ITEM

Soldering Tool Soldering and unsoldering Wattage rating: 47-1/2

Soldering

Suction Device Removes molten solder

Resin

Solvent soldered

Solder Component

Protective Contamination and corro-

Coating sion protection corrosion-prevention properties Humiseal Protective Coating,

Tip*

(Flux)

Soldering and unsoldering Shape: pointed

from

Removes

cation

printed-circuit board repair, and wiring connections preferred

USE

Tip

connection

excess

flux

from

area

before appli-

of

protective coating bonding agent

replacement,

Must base

Resin

(60/40 tin/lead), 18

Good

DESCRIPTION

Temp: 8500to

not

dissolve etched

board material

(flux)

core, high

electrical

to

56-1/2W

900°F

circuit

or

conductor Aceton

tin

content

gauge

(SWG)

insulation,

RECOMMENDED MODE

Ungar

#776

Handle

Ungar

#4037

#PL111*

Ungar

Soldapullt Arleta, California

Freon

Lacquer Isopropyl Alcohol (100%

Krylon

Type 1 B 12 by Columbia Technical Corp., New

by Edsyn Co.,

Thinner

R**

#1302

York

Heating

Woodside

with

Unit*

L

dry)

77,

*For

working on etched boards;

to

800°

F)

and Ungar #P L 113 1 /8-i nch

**

Kryton,

Inc., Norristown, Pennsylvania

Part 2

for

general purpose

ch

isel

work,

use

Ungar

#1237

Heating

ti

p.

Unit

(37.5W,

tip

temp

of

750°

4-1

Repair and Replacement

4-5. The following procedures are recommended when component

replacement

is

necessary.

a.

Remove defective component from board.

b.

If

component was unsoldered, remove solder from

mounting holes with a suction device (table 4-1)

or

a wooden

toothpick.

c. Shape the leads

of

replacement

component

to

match mounting hole spacing.

d. Insert component leads into mounting holes and

position

component

as

original was positioned. Do

not

force leads into mounting holes; sharp lead ends may damage plated-through conductor.

Note

Although

not

recommended when

both

sides

of the PCA are accessible, axial lead components such

as

resistors and tubular capacitors can be

replaced without soldering.

Clip ends

of

defective component near body. Straighten leads left in board. Wrap leads

of

replacement component

one

tum

around original leads. Solder wrapped

connection and clip

off

excess leads.

4-6. REPLACEMENT.

4-7. The 7970B/7970C

is

of

modular design.

All

major

transport assemblies are easily accessible for repair

or

replacement. The following paragraphs describe replacement of

critical transport assemblies. Refer

to

section VI for de-

tailed views

of

mechanical assemblies.

4-8. TAPE ROLLER AND BEARING ASSEMBLY.

4-9. The tape rollers are precision referenced

to

a step

on

the

mounting shaft. The bearings are very critical

to

preloading. When replacing the tape roller and bearing assemblies refer

to

section V for adjustment procedures

to

prop-

erly preload the bearings.

4-10. CAPSTAN (10 - 37.5 IPS UNITS ONLY).

4-11. The capstan replacement requires

that

the capstan

motor

assembly

be

removed from the transport. The posi-

tion

of

the

capstan

is

referenced

to

the mounting surface

of

the

capstan

motor

assembly, The following procedures de-

scribe capstan replacement.

a.

Disconnect capstan

motor

and tachometer connec-

tors from capstan servo printed-circuit assembly.

b. Remove four socket-head screws securing the

cap-

stan

motor

assembly

to

the transport casting.

4-2

7970B/7970C

c. Loosen two socket-head set-screws holding the cap-

stan

to

the

motor

shaft and remove capstan.

d. Place the capstan

on

the

motor

shaft and using a scale with 1/64-inch graduations, position the front edge (top)

of

the capstan 1-1/32 (±1/64) inch from the

motor

mounting surface. (See figure 4-1.)

e. Tighten capstan set-screws and reinstall capstan

motor

assembly.

f.

Reconnect capstan

motor

and tachometer connec-

tors

to

capstan servo printed-circuit assembly.

Figure 4-1. Capstan

PositiEll1

4-12. CAPSTAN (37.6 - 45 IPS UNITS ONLY).

4-13. The capstan replacement for 37.6 - 45 ips units

is

the same

as

the

10

- 37.5 ips units except

that

a single screw

secures the capstan

to

the

motor

shaft. The capstan position

on

the shaft

is

not

adjustable.

4-14. REEL

HOLDDOWN-ASSEMBLY.

4-15. The replacement

of

the reel holddown assembly

is

not

critical; however, an adjustment

of

the reel retaining

knob must be made

to

ensure

that

the tape reel mounts

firmly and does

not

slip. Refer

to

section V for a descrip-

tion

of

the reel retaining knob adjustment.

4-16. TENSION ARM ASSEMBLY.

4-17. The replacement

of

the tension arm assembly

is

not critical; however, the tape rollers are critical to preloading. The following procedures describe replacing the tension arm assembly.

a. Disconnect the tension arm photosense connector

from the reel servo assembly.

Part 2

7970B/7970C

b. Using retaining ring pliers, remove

ring holding tape roller

to

tension arm. (See figure 6·6.)

outer

retaining

b. Remove the two screws

amplifier assembly

to

Repair and Replacement

that

secure

the transport casting.

the

read pre-

c. Note

the

positions

of

the shims and washers and remove the shims, washers, and tape roller from tension arm shaft.

d. Remove the tension arm spring.

e.

Remove the three screws and washers

Mount

to

the

the tension arm

f.

ble in reverse order

g.

Perform adjustment procedures described in sec-

tion

V.

the transport casting.

new tension arm assembly and reassem·

of

disassembly.

that

secure

4-18. PHOTOSENSE ASSEMBLY.

4-19. The photosense assembly ative

to

the tape path

describe replacing the

a.

Loosen (do

is

critical. The following procedures

EOT/BOT photosense assembly.

not

remove) the

(EOT/BOT) position rel-

two

screws

that

secure

the photosense assembly to the transport housing.

b. Remove the photosense assembly from the housing.

c. Note the color-coding

of

the wires attached

to

the

photosense assembly and remove the wires.

d.

Strip and solder the wires

assembly in the same positions noted in step

to

the new photosense

"c."

e. Inspect the photosense insulator remaining on the transport. with a new insulator

and tighten the screws just enough

If

the insulator

is

damaged, remove and replace

(HP part number 07970-01176).

f.

Place the new photosense assembly into position

to

allow the position

of

the photosense assembly to be shifted.

g.

'Thread a reel

of

tape on the transport and position the photosense assembly 1/8-inch from the tape. Ensure that

the face

of

the assembly

is

parallel

to

the tape path.

h. Tighten the photosense mounting screws.

4-20. MAGNETIC HEAD ASSEMBLY.

4-21. The magnetic head assembly contains all critical tape path components.

Use

extreme care in handling the

assembly. The following procedures describe replacing the magnetic head assembly.

a. Disconnect

the

magnetic head assembly connectors from the read preamplifier assembly and write interconnect assembly (units equipped with write data modules).

c.

Position the read preamplifier assembly

access

to

the magnetic head assembly.

d. Remove the three hex-head screws

that

to

allow

secure the

magnetic head assembly to the transport casting.

e. Carefully remove the magnetic head assembly.

CAUTION

The magnetic head assembly contains all critical

not

tape path elements. Do

or

cleaner, port

head assemblies to contact the trans-

casting.

magnetic head assembly

head surface

f.

Carefully place the new head assembly into posi-

tion and secure it

Use

extreme care in positioning the

or

misalign the tape

to

the transport casting with mounting

allow the guides,

as

not

to

scratch the

path

elements.

hardware.

g.

Replace the read preamplifier assembly and recon-

nect the magnetic head assembly connectors.

4-22. REEL

SERVO PRINTED-CIRCUIT ASSEMBLY.

4-23. The reel servo printed-circuit assembly replacement is

not

critical; however, the mounting bracket

bly also serves

as

a heatsink. Prior

to

installing a new

paired reel servo printed-circuit assembly, ensure

transport mounting surface and the assembly mounting

of

the assem-

that

or

re-

the

sur-

face are well coated with a thermal-compound.

4-24.

CAPSTAN SERVO PRINTED-CIRCUIT ASSEMBLY.

4-25. The capstan servo printed-circuit assembly ment

is

not

critical; however, the assembly contains a strapping network in the form position

If

the unit

of

this connector on the assembly

is

operated with the connector removed

of

a dummy

DIP

replace-

connector. The

is

very critical.

or

in the wrong position, damage to the unit may result. Refer to figure

7-10, Capstan Servo Assembly Schematic Diagram

determine correct position

4-26. The mounting bracket circuit assembly also serves

of

the connector.

of

the capstan servo printed-

as

a heatsink. Prior

to a new or repaired capstan servo assembly, ensure transport mounting surface and the assembly mounting

to

installing

that

the

sur-

face are well coated with a thermal compound.

Part 2

4-3/4-4

7970Bj7970C Adjustment Procedures

SECTION

ADJUSTMENT

5-1. INTRODUCTION.

5-2. This section provides adjustment procedures for

the tape transport

Tape

Units. The adjustment procedures consist ical adjustments, power supply adjustments, capstan servo adjustments, and reel servo adjustments.

5-3. TEST EQUIPMENT REQUIRED.

5-4. The following test equipment

equivalent capacity

a. A means drive rates specified in the procedure. The trol

and

Status Test Board and will meet the needs for all adjustments. Computer eration

HP 140A).

is

also suitable.

b.

HP

c. HP

140A

1421A

of

the

HP 7970Bj7970C Digital Magnetic

of

mechan-

or

equipment with

is

required

of

dynamically operating the tape unit

Oscilloscope.

Time Base and Delay Generator (for

to

perform the adjustments.

HP

is

available

as

a service accessory

13191A

at

Con-

op-

V

PROCEDURES

to

the bearing, then the preload washer, followed by shims

to

remove all end play. Proper preload will exist when there

is

one shim beyond the number required

end play.

5-10. Tape roller loading must

or

in figure 5-1. To obtain the proper tape roller loading,

ceed

5 inch-pounds.

5-1. taining Ring Corp P100; taining ring.

Add'/remove flat washers (3 removed.

tape roller must spin freely. freely, loading

Shim thickness

be performed whenever the tape roller

repaired. The exploded tape roller assembly

as

follows:

a.

Assure

that

b.

Install assembly components

Use

Retaining Ring Pliers (Waldes 18-23; Industrial Re-

c. Check tape roller bearing assembly

d.

Spin bearing assembly and check for drag. The

is

excessive; recheck end-play clearance.

is

0.005 inch, nominal.

is

critical. Tape roller loading

brass

nut

(figure 5-1, 8)

or

equivalent). Avoid distorting

or

2) until end-play

If

the tape roller does

to

just remove the

is

dismantled

is

illustrated

is

torqued

as

indicated in figure

(6)

end-play.

is

not

pro-

to

re-

just

spin

d.

HP

1402A

e.

HP 5245L Counter.

f.

HP

5245L).

5-5. In addition Test Tape

5-6.

5-7. Transport mechanical adjustments consists

roller, reel servo arm, write enable switch, and reel retaining

knob

5-8.

5-9. in the shaft stances should any adjusting shims be placed between the inner bearing and this step. Shimming end

HP

MECHANICAL ADJUSTMENTS.

adjustments.

TAPE ROLLER.

All

tape rollers are precision referenced on

of

the roller. Assembly should consist

Dual-Trace Amplifier (for

5265A Digital Voltmeter Plug-In (for HP

to

the listed test equipment, Transport

part number 5080-4525

which they are mounted. Under no circum-

is

required.

is

HP

to

the step

done at the

of

one shim next

140A).

of

tape

outer

5-11.

5-12. The tension arm adjustments consist positioning sense mask and positioning the limit switches relative

tension arm.

5-13. is photosense mask does cell assembly. There should be a nominal clearance

inch minimum between the cell and the

mask.

5-14. switch mounting bracket pivots

the tension arm rubber stop. The hole for the adjacent screw

is

this screw locks the mounting bracket in position after

pletion switch are also elongated, providing slight additional limit switch adjustment movement. To position the limit switch,

rotate

the following conditions:

microswitch should be approximately

the arm diameter

TENSION ARM.

the

photosense assembly relative to the photo-

TENSION ARM PHOTOSENSE. This adjustment

critical. Adjust

TENSION ARM LIMIT SWITCHES. The limit

elongated

of

the bracket

a.

When arm

as

required

to

provide limit switch positioning adjustment;

the adjustment. Mounting holes for the micro-

and/or

is

fully against bumper, the roller on the

without

to

assure

that

not

touch

the photosense lamp and

on

the screw

adjust height position

at

being over center.

the tension arm

outer

the high

of

side

that

to

properly

to

the

of

0.010

of

the

mounts

com-

achieve

point

of

Part 2

5-1

Adjustment Procedures

1

RETAINING

2 0.005 WASHER

3.

CRESCENT WASHER

0.010 WASHER

4

ROLLER RETAINING BRASS

NUT

TAPE

ROLLER

ASSEMBLY

5 G

7. 8 CRESCENT WASHER

9.

7970B/7970C

RING

SHAFT

Figure 5-1. Tape Roller and Bearing Assembly, Exploded View

b.

When the arm

is

within

1/8

inch

of

the bumper stop, the microswitch must operate. Also there must be further positive movement point

at

which the switch closes and the tension arm

of

the switch arm between the

is

in

full stopped condition against the rubber bumper.

c. Verify firmation limit switches.

of

that

all

screws are tight prior

"a"

and

"b."

Repeat adjustment for all three

If

background noise permits, switch opera-

to

final con-

tion can be checked audibly; otherwise connect a suitable ohmmeter verify

5-15.

5-16. The write enable switch must be positioned sure clearance when operated with a reel the write enable ring installed (reel assure

with a reel

across the switch terminals.

that

power

is

not

applied

If

to

the tape unit.

ohmmeter

WRITE ENABLE SWITCH.

that

is

file protected) and

both

retraction and operating clearance when used

that

has the write enable ring installed. These

does

is

not

used,

to

as-

have

to

conditions will be established when the proper dimensional relationships exist between the write enable sensing finger and

the

outer

face

of

the reel turntable. To obtain these required dimensional relationships, perform the adjustment procedure

in

the order indicated. (See figure 5-2.)

a.

Loosen switch

Sl

mounting screws.

b. Manually place the sensing finger even with the

edge

of

the turntable. With power removed, adjust the posi-

tion

Sl

until an audible click indicates

that

closed.

c. Tighten switch

Sl

mounting screws.

d. Apply power and manually place the sensing finger

even with the turntable. Verify

that

the solenoid energizes

and completely retracts the sensing finger.

e. Adjust the reel turntable flange diameter clearance

as

follows:

(1) Loosen write enable assembly mounting

screws.

(2) Position the write enable assembly so

sensing finger will clear the reel flange eter throughout solenoid travel.

(3) Tighten write enable assembly mounting

screws.

5-17.

5-18. This adjustment may require some correction during the life

REEL RETAINING

is

KNOB.

made during manufacture

of

switch

the

tape unit.

7970-C-038

Sl

that

diam-

is

the

but

5-2

Part 2

7970B/7970C

WRITE

SENSING

ENABLE

FINGER

SWITCH

MOUNTING

WRITE

ENABLE

(ENERGIZES

SCREWS

SWITCH

SOLENOIDI

Adjustment Procedures

Sl

7970-506

Figure 5-2. Write Enable Assembly

is

When the locking lever possible of

to

place the reel over the rubber with a minimum

interference. When the locking lever resistance should be encountered sed. In the locked position, move the reel by hand. piece

of

masking tape

mark placed in alignment

not become misaligned by more than

of

operation. To correct tape reel slippage, release locking

working properly,

as

it

should

If

slippage

on

the reel, another

on

both

the rubber

is

pieces

1/8

it

should be

is

closed, positive

is

compres-

not

be possible

to

suspected, place a

on

the hub. A

of

tape should

inch in

16

hours

lever and loosen the pozidrive screw, rotate the reel retainer knob clockwise, and tighten screw. Repeat until tape reel

mounts firmly and does

not

slip.

5-19. ELECTRICAL ADJUSTMENTS.

5-20. The electrical adjustments critical and must be performed in the following sequence:

a.

Power supply adjustments.

b.

Capstan Capstan servo forward and reverse drive speed ad-

c.

motor

offset current adjustment.

justments.

d.

Capstan servo high-speed forward adjustment.

e.

Capstan servo high-speed reverse adjustment.

f. Capstan servo ramp slope adjustment.

g.

Reel servo adjustments.

of

the tape unit are very

WRITE

ENABLE

SWITCH

S2

5-21.

5-22. Only one adjustment lated supplies. The adjustment control cuitry for the +12 volt supply

the value operating tolerance. The value

plies

trol

bly. Voltage

POWER SUPPLY ADJUSTMENTS.

is

provided for the three regu-

is

but

is

adjusted

of

the +5 volt supply, which

of

the +12 and

is

established by a precision resistor network. The con-

is

located

on

the power regulator printed-circuit assem-

is

correctly adjusted when the following con-

ditions are met:

a.

+5

justment

b. c.

± 0.050 Vdc. (Adjust

is

required.)

+12 ± 0.360 Vdc.

-12

± 0.360 Vdc.

to

±0.010 Vdc when ad-

Note

Final reel servo adjustments must be made after the capstan servo adjustments. The capstan speed must be within tolerance in order adjust

the

reel servo. However, tension maintained in order adjustments.

If

to

make the capstan servo

the tape unit does tension, perform the reel servo adjustments tially, complete the capstan servo adjustments, and repeat the reel servo adjustments.

located in the cir-

to

establish

is

held

to

a tighter

-12

volt sup-

to

properly

must

be

not

maintain

ini-

Part 2

5-3

7970Bj7970C

WRITE ENABLE

SWITCH

(ENERGI

SOLENOIO)

WRITE

ENABLE

SENSING FINGER

..

Adjustment Procedures

SWITCH MOUNTING

SCREWS

WR

ITE ENABLE

SWITCH

S2

S1

___

--I

7970-353

Figure 5-2.

Write

Enable Assembly

Part

2

5-3

Adjustment Procedures

5-23. CAPSTAN MOTOR OFFSET CURRENT

ADJUSTMENT.

5-24. Prior

to

making the capstan

motor

offset current

adjustment, verify

that

the power supply voltages have been

adjusted. Figure

5-3 shows the location

of

the capstan

motor

offset adjustment variable resistor.

5-25. Connect a suitable dc voltmeter (capable

of

resolu·

tion

to

±5 mv dc) across a 3-ohm resistor (R21

or

R22) con·

nected in series with the capstan

motor

. The common side

of

the resistance

is

associated with pin 2

of

CJ1 and the high

or

motor

side

is

associated with pin 2

of

CJ2.

7970B/7970C

5-26.

Load the tape transport and be sure tape

is

stopped. Adjust OFFSET control until voltmeter reading

is

minimum. An acceptable minimum

is

any value which

is

between +0.100 Vdc and

-0.100

Vdc. Typical adjustment

at room ambient temperature (25°

C)

will be in the order

of

±0.080 Vdc.

5-27. CAPSTAN SERVO FORWARD AND REVERSE

DRIVE SPEED ADJUSTMENTS.

5-28. Prior to performing the servo forward and reverse drive speed adjustment , ensure

that

power supply voltages

REVERSE SYNCHRONOUS TEST

SWITCH

REVERSE SYNCHRONOUS ADJUSTMENT

___

FORWARD SYNCHRONOUS

TEST

SWITCH

---FORWARD SYNCH

RONOUS

ADJUSTMENT

RAMP

ADJUSTMENT

PREAMPLIFIER TEST POI

NT

HIGH

SPEED

FORWARD

TEST

SWITCH

HIGH

SPEED FORWARD ADJUSTMENT

HIGH

SPEED REVERSE ADJUSTMENT

OFFSET ADJUSTMENT

FWD/REV

TEST

POINT

(BIPOLAR

RAMP

GENERATOR)

CAPSTAN

SERVO

SPEED

SELECTION

PLUG

(DIP

DUMMY

PLUG

)

SHOWN

IN

25

TO

45

IPS

POSITION

USING

CAPSTAN

ASSEM

BL

Y

07970-60141

TACHOMETER TEST

POINT

7970-518

Figure 5-3. Capstan Servo

PC

Assembly, Test Points and Adjustments

5-4

Part 2

7970B/7970C

Adjustment Procedures

and offset current are within tolerance. Figure 5-3 shows the location

of

service switches and forward and reverse

drive adjustment potentiometers.

is

5-29. Accurate adjustment counter) data bits that have been recorded with high age

accuracy. The 5080-4525 Test Tape has bit-to-bit

curacy

of

better than 0.1 percent when measured over 2000

bits

or

more. In using this tape, it

that

there are two data bits for each cycle counted when the

is

counter

connected

nal, and also

that

to

the

the frequency

based on reading (into a

is

important

to

preamplifier analog

at

other

than the specified

aver-

recognize

output

ac-

sig-

tape speeds may be calculated on a direct ratio basis. The signal used for the following adjustments appears in

preamplifier channel 3 of nine-track units and preamplifier channel 6 nal bit distance

mode using

counter indication The values for speeds

of

seven-track units. The test tape provides a

of

10,000

a.

b. Adjust the

Hz

at

of

0.0015 inch.

a tape speed

of

30 ips and has a bit-to-

Load test tape and place unit in forward drive

FWD

service switch (S2).

FWD

synchronous control (R34) until

is

correct for the tape speed involved.

of

25

ips and 37.5 ips will follow.

sig-

Values for other speeds may be readily calculated by direct

ratio

to

speed and application

of

the percentage tolerances

indicated.

c. For 25 ips speeds, the counter indication should be 8,333 ± is

necessary

Hz when adjustment

as

long

as

counter indication

is

completed.

No

adjustment

is

within ±65

Hz.

16

d. For 37.5 ips speeds, the counter indication should be

12,500

within ±100

± 25

Hz.

No adjustment

is

necessary if reading

is

Note

If

high-speed forward

tape units equipped with parity options and

is

required for seven-track

having normal drive speeds less than 15 ips, highspeed mode must

not

exceed a factor

of

12

times the normal drive speed.

5-32.

CAPSTAN SERVO HIGH-SPEED REVERSE

ADJUSTMENT.

5-33. The high-speed reverse adjustment

the high-speed forward adjustment, except

is

REWIND control

used to place the reverse mode and the high-speed reverse variable resistor

5-34.

CAPSTAN SERVO RAMP SLOPE ADJUSTMENT.

(R60, figure 5-3)

is

used.

unit

is

that

in

the

(-160)

identical

the local

high-speed

adjustment

to

5-35. The ramp slope adjustment determines the start

both

and stop distances for The following procedure describes how of

the bi-polar ramp generator on the capstan servo sembly. This adjustment sets the start distance inch. The point

top

of

the ramp

ofthe

voltage waveform

a.

Operate the tape unit in a forward-stop-forward

forward and reverse drive modes.

to

adjust the slope

PC

as-

to

0.1875

is

rounded, therefore, the 90% is

used. (See figure 5-4.)

mode.

b. Connect an oscilloscope

point

on the capstan servo scope with the negative going edge mand. (Test or

test point CF

point 9 of

of

the control and status

the control and status test board.)

to

the FWD/REV test

PC

assembly. Sync the oscillo-

of

the forward com-

PC

assembly

e. Repeat steps

"a"

and

"b"

with unit in reverse drive

mode.

5-30.

CAPSTAN SERVO HIGH-SPEED FORWARD ADJUSTMENT.

5-31. The high-speed forward adjustment principles and requirements are the same adjustment. Ensure

as

the forward and reverse drive

that

all previous adjustments are within

tolerance.

on

a. Load the test tape

to

a counter

the appropriate channel preamplifier

the transport and connect

output.

b. Place unit in high-speed forward mode with the high-speed forward use the high-speed forward just speed until counter indicates 53,333 ± justment

is

required if counter indicates between 52,533

(+160) service switch (figure 5-3), and

(+160) adjustment (R53)

100

Hz.

to

ad-

No ad-

and 54,133.

Part 2

7970-476

1-1.

---T-----I"I

----90%

/----WAVEFORM

~FORWARDCOMMAND

FWD/REV TEST POINT

Figure 5-4. Start/Stop Ramp Time

AT

100%

18

DIVISIONS)

17.2

DIVISIONS)

5-5

Adjustment Procedures

c. Adjust the capstan servo

trol (See figure 5-3.)

to

obtain the time listed in table 5-1

for tape unit synchronous speed.

control

the 90%

of

the oscilloscope

point

may be conveniently measured.

to

Note

On

HP

180 Oscilloscopes, the vertical spacing a special horizontal time scale which may be used

to

measure the time

90% level.

Table 5-1. Capstan Servo Start/Stop Time

SPEED (IPS)

12.5 26.1

18.75

22.5 25

37.5 8.1

45

PC

assembly RAMP con-

Use

the vertical gain vernier

expand the waveform so

is

at

7.2 divisions at

the

TIME

(90%)

ms

17.1ms

14.1

ms

12.6

ms ms

6.6

ms

that

7970B/7970C

5-36. REEL SERVO ADJUSTMENTS.

5-37. Load a short length bring

to

load point. The following adjustments determine the peak deflections deflection desired

of

is

a function At the highest speed (45 ips) the deflection tension arms deflect

side

of

the casting, At lower speeds the 25 ips the deflection

ips). Due swing

to

non-linearity

of

the tension arm may be unsymmetrical in the for-

to

both

amount is

of

tape

onto

the transport and

the tension arms. The amount

of

the synchronous speed.

is

set so the

the

outer

marks located on the back

in forward and reverse drive modes.

of

deflection

about

half (25/45) the

of

the tension arm transducer the

is

smaller (Le.,

amount

at

of

at

45

ward and reverse drive modes. (This will mean the tension arm will is 200 feet

not

be centered when there

is

no tape motion and

normal.) With the supply reel loaded with approximately

of

tape, rotate the supply (upper) variable resistor

(R106) fully clockwise and run the tape unit in the forward

mode. Rotate the supply (lower) variable resistor clockwise for the proper deflection. put

in reverse drive and make sure the

is

the same

as

in forward drive.

position until symmetrical swings

If

of

Stop

tape motion and

amount

not,

readjust the mask

the

proper achieved. Repeat procedure for the take up reel with mately 200 feet

of

tape on the takeup reel.

counter-

of

deflection

amount are

approxi-

5-6

Part 2

7970B/7970C

Replaceable Parts

SECTION

VI

REPLACEABLE

PARTS

6-1.

INTRODUCTION.

6-2. This section provides information for ordering replacement parts for the tape transport

of

the HP 7970B /

7970C Digital Magnetic Tape

Units.

6-3. This section contains assembly parts lists, support-

ing illUstrations, ordering information, and a

part

number

cross reference.

6-4. ASSEMBL Y PARTS LIST.

6-5. The assembly parts list presents a breakdown

of

all

replaceable parts

of

the tape transport. The information

contained in the lists are under the following headings:

a.

FIGURE & INDEX NO.

b. PART

NUMBER.

c. DESCRIPTION.

d.

UNITS PER ASSY.

6-6. FIG

URE AND INDEX NUMBER.

6-7. The figure and index number column identifies the figure

that

illustrates each listed item and the index number

that

identifies the item

on

the illustration.

6-8. PART

NUMBER.

6·9 .

The

part

number column provides the Hewlett-

Packard

part

number for each item listed in

the

assembly

parts list.

6·10. DESCRIPTION.

6-11. The description column describes the items within the equipment. An indented column arrangement

is

used

to

show the relationship between a part and

the

parts next

higher assembly. The

top

assembly

of

each listing appears in

Part 2

indention 1. Primary subassemblies

(of

the

top

assembly)

and attaching parts appear in indention 2. This method

of indention is continued through indention 3, 4, etc, until all replaceable parts are listed. Attaching parts are listed

im-

mediately following the

part

they attach. Attaching parts

are identified by the abbreviation (AP) enclosed

in

paren-

thesis at the end

of

the description.

6-12. Reference designation and manufacture

informa-

tion (if applicable)

is

also included in the description col-

umn.

6·13. UNITS PER ASSEMBLY.

6·14. The

quantity

shown in the units per assembly col-

umn

reflects the total quantity

of a part

required by the

next higher assembly

of

that

part. This

quantity

is

not

neces-

sarily the total used for the complete equipment. The ab-

breviation AR

is

used

to

indicate usage

as

required

of

a

particular item. The abbreviation

REF

is

used

to

indicate

that

the quantity

of

an item used

per

assembly

is

listed in

the next higher assembly

of

the assembly

part~

list.

6-15.

ORDERING

INFORMATION.

6·16. To order replacement parts, address the

order

or inquiry

to

the local Hewlett-Packard Sales and Service Office.

(Refer

to

the list

at

the end

of

this manual for addresses.)

Specify the following information for each

part

ordered.

a. Identification

of

the unit, kit,

or

assembly con-

taining the part.

b. Hewlett-Packard

part

number for each part.

c. Description

of

each part.

d. Circuit reference designation (if applicable).

6-17. PART NUMBER CROSS REFERENCE.

6-18. Table 6-1

at

the end

of

this section provides a

cross reference between Hewlett-Packard

part

numbers and

manufacturer's

part

numbers .

6-1

HP 7970B, 7970C Operating And Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual