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DEC-00-HZT

December 1969

52 pages

Original

3.1MB

Document:	dec-00-hzta-d
Order Number:	DEC-00-HZT
Revision:
Pages:	52
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/dec-00-hzt/dec-00-hzta-d.pdf

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Ist Printing November I966
2nd Printing February I967

3rd Printing June I967
4th Printing October I968
5th Printing November I968
6th Printing May I969

Instruction times,

operating speeds and the like are in—

cluded in this manual for reference only; they are not to
be taken as specifications.

The Following are registered trademarks of Digital
Equipment Corporation, Maynard, Massachusetts:
DEC

PDP

FLIP CHIP

FOCAL

DIGITAL

COMPUTER LAB

CONTENTS

Page
CHAPTER 1
INTRODUCTION AND DESCRIPTION

1.1

General Description

1—11

1.2

Scope othanual

1—2

1.3

Pertinent Documents

1—2

1.3.1

AAanuak

1—2

1.3.2

Engineering Drawings

1—u2

1.3.3

New Module News Bulletins

1.4

Functional Description

1-3

1.5

Physical Description

1—4

1.5.1
1.6

Electrical Details
TU55 Performance Characteristics

CHAPTER 2
THEORY OF OPERATION

2.1

Block Diagram Analysis

2.2

Detailed Descriptions

2.2.1

Interface

2.2.2

Unit Select Lines

2.2.3

Command Lines

2.2.4

WRITE ENABLE Signal

2.2.5

Interface Connections

2.2.6

Read/VVfite Head

2.2.7

Tape Motion Control

2.2.8

Remote or Programmed Control

2.2.9

Local (Manual) Control

2.2.10

Motor Control

2.2.11

Transport Selected Signal

2.3

Module Descriptions

2.3.1

Type R303 Integrating One Shot (Delay)

2.3.2

Type W513 Level Amplifier

2.3.3

Type G850 SCR Motor Driver

1-9

CONTENTS (Cont)

Page
CHAPTER 3

OPERATION

3.1

Introduction

3-1

3.2

Controls and Indicators

3-1

3.2.1

Operating Notes

3.3

3—1

3-1

Loading Tape
CHAPTER 4

MAINTENANCE

4.1

Equipment Required

4—1

4.2

Preventive Maintenance

4-1

4.2.1

Weekly Schedule

4—1

4.2.2

Monthly Schedule

4—2

4.3

Tape Tension and Transport Stop Adjustment

4-2

4.4,

Head Output Check

4-3

4.5

Head-Skew

4.6

Checl<

4-4

Write Enable Circuit Check

4-5

4.7

Troubleshooting

4-6

4.8

Recommended Spare

4-7

CHAPTER 5
ENGINEERING DRAWINGS

5.1

Introduction

5-I

5.2

Circuit Symbols

5-I

Logic Signal Symbols

5-I

5.3.1

Logic Levels

5-I

5.3.2

FLIP CHIP Pulses

5-I

5.4

Semiconductor Substitution

5-4

5.3
.

ILLUSTRATIONS
1-1

Type TU55 DECtape Transport

1-1

1-2

Hub and Reel Assembly

1-5

1—3

Arrangement of DECtape Head

1-6

Type TU55 DECtape Transport, Rear View

1-7

ILLUSTRATIONS (Cont)

Page

‘

1—5

TU55 Interface Connections

1-8

2-1

DECtape Transport TU55 Block Diagram

2-1

2-2

Head Connections

2-4

2-3

Schematic of R303 Integrating One-Shot

2-10

2—4

Schematic of G850 SCR Motor Drive

2-1]

4-1

Module Adiustment Trimports

4—3

5—I

DEC Symbols

5-2

FLIP CHIP R-Series Pulse

5-4

5-3

FLIP CHIP B-Series Pulse

5-4

Module Schematics
Solid State DECtape Transport, TU55—0—2

5-5

Module Utilization List, TU55-0-5

5—7

Bus Bar For TU55, TU55-0-4

5-7

Relay, C7851

5-8

Diode Cluster, R002

5-8

Inverter, R107

5—9

Diode Gate, RIII

Dual Flip-Flop, R202

5-10

Integrating One-Shot, R303

5—10

Solenoid Driver, W040

5-I'l

Level Amplifier, W513

5-11

TABLES
1-1

Summary of Equipment Characteristics for the TU55 DECtape Transport

2-1

Motor and Brake Operation Truth Table

2-9

3-1

Functions of Controls and Indicators

3-2

4-1

Recommended Maintenance Equipment

4-1

4-2

Recommended Spare Parts

4-7

Semiconductor Substitution

5-4

CHAPTERl
INTRODUCTION

I .I

AND

DESCRIPTION

GENERAL DESCRIPTION
The Type TU55 DECtape Transport (see figure 1-1) is a solid—state,

tape

bidirectional, magnetic-

handlingdevice designed and manufactured by the Digital Equipment Corporation (DEC) for

use

DEC digital computer systems.

When used with a suitable DECtape control system, the TU55 provides a

fixed-address magnetic-tape facility for high—speed loading, readout, and program updating.

The DEC-

tape control system directs the transport to read forward or in reverse, to write forward or in reverse,

stop, and to go.

The TU55 contains tape handling elements, drive mechanisms, and solid-state switching

circuits which switch the tape head onto a master bus system and

control unit.

interpret command instructions from the

The highly reliable solid-state switching circuits in the TU55 are completely compatible

with the Type 555 DECtape Transport (which uses relay switching) and may be used to modify and

expand systems employing this type of transport.

we!!!“
'

JuiiiE

smut“!

mark“

h” gunmen

Figure 1-]

Type TU55 DECtape Transport
I-l

SCOPE OF MANUAL

l .2

This instruction manual is intended to aid personnel in the maintenance of the TU55 DECtape

Transport. The equipment is discussed primarily from a maintenance point of view, but some information
is given on the operation of its associated controls and indicators.

The documents listed below provide

operational information required for programming.
Since the tranSport is one element of a computer/control/tranSport system, the reader should
know the basic internal operations of both the computer and control.
sections concerning program

Of special importance are the

interrupts, programmed in/out transfers, and the databreak facility in the

computer; and the select and motion control logic in the external DECtape control.

Detailed descrip-

tions of the tape format, instruction repertoire, and programming practice for using the TU55 with a

particular computer is described in the user handbook for the computer.

Control information for the

TU55 can be obtained from the maintenance manual for the DECtape control system used with the

transport

PERTINENT DOCUMENTS

1.3

The following documents provide source information relative to the use ofvthe DECtape Trans-

port Type TU55.

Manuals

l.3.l
_

Digital FLIP CHIP Modules Catalog, C—IO5
PDP_7 User Handbook, F-75
PDP-8 User Handbook, F-85

DECtape Control 550 Instruction Manual, H-550

DECtape Control 55] Instruction Manual, H-55l
DECtape Control 552 Instruction Manual, H-552

DECtape Control TCOI

Instruction Manual, DEC-08-I3AB-D

DECtape PDP-8 Programming Manual, Digital—8—27-U

l .3.2

Engineering Drawings
A set of reduced engineering drawings for the TU55 is contained in chapter 5.

are

in addition to the complete set of full-size drawings forwarded with each TU55.

These drawings

As explained in

chapter 5 all maintenance personnel should use only the full size engineering drawings for work on the
equipment because these drawings show variations peculiar to an individual installation.

1-2

New Module News Bulletins

1.3.3

6850 SCR Motor Driver
G851

Relay

W5l3 Level Amplifier

In addition to the above documents,

complete sets of Library Programs are available for each

computer using DECtape systems.

I .4

FUNCTIONAL DESCRIPTION
The TU55 Transport provides a read/write head for recording and playback of information on

five channels of the 0.75-inch tape.
in series.

Each channel consists of two nonadiacent coils which are wired

Thus, information on one track combines with redundant information on another to create a

single signal.

Connections from the read/write head are made directly to the external control unit which

contains the read and write amplifiers as well as the command logic for the selection and remote control

of tape motion.
The left half of the front panel (see Figural-l) contains the tape deck with reels and reel

motors, tape guides, and the read/write head; the right half is the local control panel with rocker
switches for selection and manual operation.

directly control tape motion.

No capstans,

The 600-rpm induction motors that drive the reel hubs

pinch rollers, or drag pads contact the tape.

The logic circuits of the TU55 command tape movement in either direction over the read/write
heads.

Solid-state switching circuits completely control the tape drive motors.

These circuits govern

the torque applied to each reel motor to transport the tape across the head in accordance
commands (i.e., go,

with specific

forward, reverse, stop).

In normal tape movement, full‘ torque is applied to the take-up reel, thus establishing the

direction of motion.

Reduced torque, applied to the trailing reel, maintains proper tape tension. Tape

motion is bidirectional so that either reel can serve as the take—up reel.

The DECtape system uses the

so-called Manchester phase recording technique rather than an amplitude sensing technique; thus, tape

speed need not be a precisely controlled parameter. Actually, the speed varies :|:20%, depending upon
the diameter of the tape pack on the take-up reel.

electromagnetic brake mounted

shaft achieves a positive stop by braking the trailing reel at the

end of

reel motor continues to apply partial torque to take: up tape slack.
one

motion command.

each motor
The take—up

Whenever the tape is motionless,

of the two reel brakes is applied opposite to the direction of the last tape movement.

Tape movement is controlled either by commands originating in the computer and applied to
the TU55 via a suitable DECtape control system,

by commands generated through manual operation

of rocker type switches located on the front panel of the transport.

Typical DECtape control systems

which allow transfer of information between the computer and the TU55 are as follows:

Computer

Typical DECtape Control System

PDP—l , —4 and -7

Type 550

PDP-é

Type 551

PDP-5 and -8

Type 552

PDP—8

TCOl

PDP—9

TC02

Manual control is used to mount new reels of tape on the TU55 or as a quick maintenance check for
proper operation of the control

External
read or write tape.

logic in moving the tape.

DECtape control systems may control up to eight individually addressed TU555 to
The operator may select the address of each drive by adiusting the thumbwheel

selector at the center of the TU55 local control panel (see figure

1-1). The operator may also place

the drive off—line by a setting on the same thumbwheel or by switching the drive for local operation.
In local operation, the head is disconnected and the rocker switches on the local control panel regu-

late tape motion

PHYSICAL DESCRIPTION

i .5

All components of the TU55 are mounted on a preformed and assembled chassis.
that allow easy access to the top,

sides, and rear of the drive hold the chassis in a standard DEC bay.

Double doors in the front and rear are held closed by magnetic latches.
are

Roller slides

mounted on the rear of the DEC bay.

Power supplies and controls

Generally, the transport is mounted with others in the same

bay that contains the DECtape control system.
The tape deck is machined from 3/8—inch cast aluminum plate and held to the chassis by cap
screws

the corners.

Reel motors, tape guides and the head are secured only to the deck.

arrangement preserves the integrity of the tape alignment by the rigidity of the deck plate.

This

Heavy

extruded aluminum plates at the top and bottom front of the chassis serve as bumpers to protect the

deck and control panel.
sides by brackets.

field.

The head is mounted in direct contact with the deck and is secured at both

Head azimuth is set during manufacture of the drive and cannot be adiusted in the

CAUTION
No attempt should be made to loosen the brackets and change the head

position.

Reel motors are held by four cap screws (hidden by the reel hubs) from the front of the deck.
At the rear of the shaft (which extends from both ends) is the electromagnetic brake.

shaft has a flat for securing the reel hub by a single Allen—head set screw.
rear

At the front, the

The hubs are flanged at the

and have an annular spring resting in a slot cut into the reel circumference.

Beneath the spring in

the slot is a rubber ring seal which causes the spring to protrude above the slot to secure the reel

figure l-2). The reel is a l—piece mold of phenolic composition.
of the reel fits the hub.

In front,

(see

The inside circumference at the back

however, the inside circumference is slightly larger, allowing the
The clearance between the rear of the reel hub

hub spring to expand outward and to secure the reel.

and the tape deck is nominally 15 mils, but may vary on individual machines to guarantee proper tape

alignment in the guides.

The guides are machined from aluminum and have a curvature designed to

maintain air-film lubrication between the tape and guides as long as tape is in motion.
on

the top chassis plate continuously blows cooling air over the reel motors.
FLANGE

REEL

SPRING

L/MOTOR

SHAFT

\HUB
RING

SEAL-Hc_-_

REEL—”ll

\-—F——— DECK PLATE
SPRING

W
Figure 1-2

Hub and Reel Assembly
1-5

A fan mounted

The redundantly paired tracks that form the five channels on the head are illustrated sche-

matically in figure 1-3.
control information.

Three track pairs are used for data; the remaining pairs are used as timing and

The two timing tracks are on the outside at opposite sides of the tape.

Just inside

these are the two tracks for the mark channel, the contents of which signify to the external control the

type of information in the data channels.

The six tracks for these data channels are grouped at the

center, where they are least affected by skew.

Since writing may take place in the data channels

while reading takes place simultaneously in the timing and mark channels, the tracks for the latter

channels are separated slightly from the data channel tracks to allow room for additional shielding.

(’

TAPE
DECK

PLATE

AUGMENTED
SPACING

STANDARD

.088"

1
.

SPACINGS“
.073"

‘

UNA
CHAN
1
DATA
CHAN
2
DATA
CHAN
3

Figure 1-3

1.5.1

MARK

CHANNEL

HMWG

CHANNEL

Arrangement of DECtape Head

Electrical Details
The TU55 requires the DEC standard H 0 and —T5 vdc power levels at the terminal-tab con-

nectors on the rear

panel (figure 1-4).

These do levels are normally provided from power supplies

associated with the DECtape control system.

terminal receptacle on the rear panel.

AC power (105-125v, 60 cps) is connected at the 3-

Figure 1—4

Type TU55 DECtape Transport, Rear View

Signal connections to and from the DECtape control system are made through 18-pin and
36—pin FLIP‘ CHIP cable terminators that plug directly into the module mounting panel on the rear

panel (Figure 1—4).

Cable locations in this mounting panel are shown in Figure l—5 with respect to the

other installed modules.

The command cable terminator is a Type W023 l8—Pin Connector for the logic

signals governing selection and tape motion. The head signal connector is
36—Bit Connector For shielded cable.

double-size Type W032

Two sockets at the TU55 logic panel are reserved for the command

connector ‘and two for the information connector.

done so that TU55s may be grouped.

The pins for each pair are bussed together.

This is

Each TU55 receives its information and commands From one trans-

port in the group through one set of connectors and sends these to the next transport through another set
of connectors.

The writing current is 210 ma.

Playback peak—to-peak channel voltage is between 10 and

12 mv when the tape is up to speed.

1—7

850

G
850

002

040

1“

PANEL
FRONT

$GNAL

SGNAL

CONECTOR COMAND CONECTOR COMAND CONECTOR

303

fl
4

3“

E
0%

or:

0%
”‘t‘
Eu

4%
§c>

107

1”

1“

202

701

)-|_

mfl

m_J

0
4

LIJ

040

LzL"
.0

§<3
2“
m

9°

W513

02
3°

303

W990

Figure l-5

TU55 Interface Connections

Command signal levels from the DECtap-e control to the TU55 Transport are either ground or
-3v.

(Equivalent signals to a 555 Transport are either —3 or -15v.)

For existing systems with a con-

trol system for the 555 TranSport, exchanging a single FLIP CHIP module (a W5l3 Level Amplifier when
the TU55 Transport is connected to a control designed to drive relay Transport 555; otherwise a W990

Blank Module) allows the TU55 to accept command signals of either type.
The reel brakes and the head relay are energized by —l5v through special solenoid driver

circuits; the motors are controlled by silicon controlled rectifier (SCR) circuits that phase-switch the
HO vac line power.

The TU55 uses twelve types of FLIP CHIP logic modules (connectors excluded) as follows:
2

W040 Solenoid Driver

W5l3 Level Amplifier/W990 Level
R107 Inverter

Amplifier

R202 Dual

Flip-Flop

R303 Integrating Delay

G850 SCR Motor Driver

RI ll Diode Gate

G85l

R303 Integrating One-Shot

W023 Indicator Amplifier

R002 Diode Network

W701

Relay Module
Input Network

All modules are mounted on a dip-soldered epoxy board with I8 gold-plated contacts at one
end (36 on double-height modules) for connection to the mounting panel receptacle, and a plastic handle

bearing the type number at the other end.

Three contacts on each module are reserved for supply voltages:

A and B supply the +10 and —l5v standard power levels; C is the ground.

1 .6

TU55 PERFORMANCE CHARACTERISTICS
A summary of the characteristics of the TU55 equipment is given in table 1-1

TABLE 1-1

SUMMARY OF EQUIPMENT CHARACTERISTICS
FOR THE TU55 DECTAPE TRANSPORT

general
Overall Size

10-1/2 in. high, 19-1/2 in. wide, 9—3/4 in. deep

Mounting

Standard 19-in. rack. Four i110-32 screws mount chassis
track assembly which holds transport.

Chassis can be extended 16-3/4 in.
surface for maintenance

beyond mounting

-15 vdc, I .0 amp maximum

Power Requirements

+10 vdc, 5O ma maximum
115 vac: i10%, 1.0 amp idle, 2.0 amp maximum current

(60- and 50-cycle models)
Commands:

Connectors

two

18—terminal FLIP CHIP female

connectors

Information:

two 36-terminal FLIP CHIP female

connectors

Cooling

Internally mounted fan

Operating Temperature

'50 to 110°F ambient

Humidity

IO to 90% relative humidity

The manufacturer of the magnetic tape for DECtape recommends 40
to 60% relative humidity and 60 to 80°F as acceptable for operating environNOTE:

ment.

Tape Characteristics

Capacity

260 ft of 3/4 in., I mil thick Mylar sandwich tape

Reel Diameter

2—3/4 in. empty reel, 3-3/4 in. for 260 ft of tape

Reel Diameter Ratio

Approx

1:4 (maximum to minimum)

SUMMARY OF EQUIPMENT CHARACTERISTICS
TABLE i-l
FOR THE TU55 DECTAPE TRANSPORT (continued)

Tape Characteristics (continued)
Direct drive hubs and specially designed guides which

Tape Handling

float the tape over the head hydrodynamically.

capstans

pinch rollers are used.

Speed

93 :12 ips

Density

350 :|:55 bits per inch

Information Capacity

bits per reel assembled into computer—length
2.7 x
words by external DECtape control

Tape Motion

Bidirectional

106

Drive Characteristics

Times given are for 90% full speed.
Start Time

£150 msec

Stop Time

_<_l 50 msec

Turn Around Time

_<_250 msec
Input Signals to Transport from Control

Commands*

FORWARD

level assertion,

normally complementary
(ground

REVERSE
GO

level 5

ground level assertion,

STOP

normally complementary levels

ALL HALT

negative level assertion used to stop
transport when computer halts

Unit Sel'ect*

SELECT 1

through SELECT 8 (the selected line will
be at ground)

Output Signal from Transport to Control
Control

WRITE ENABLE (standard DEC ground level assertion)

*Valid only when the control is operating the solid—state Transport TU55. When relay type transport
(Type 555) signals are received a conversion is made to DEC standard levels by the W5l3 Level
Amplifier which converts the -3v level to ground and the floating input to —3v.
l-lO

CHAPTER2
THEORY

OPERATION

BLOCK DIAGRAM ANALYSIS

2.l

The TU55 logic is shown in the functional block diagram of figure 2-1

trols and indicators are shown within the blocks representing the associated logic.

controls and indicators are summarized in table 3-l
tween

All front panel conThe functions of these

Diamonds indicate the direction of signal flow be—

blocl<s; an open diamond represents a signal effective (asserted) at ground; a closed diamond

resents a signal asserted at —3v.

All interface signals are received from or transmitted

One of the two connectors at the left of figure 2-l

DECtape control system.

to an

rep—

external

command and

serves as a

information signal bus to other TU55s.
A5

wRITE ENABLE
-

]
-

SELECT
LOGIC

ADDRESS

SELECT

(a)

WS'BTEE
L D

RIT

wLoch

IIIIIIIIIIII
SELECT

_
'

STOP

FORWARD

I
<—

REMOTE

_,L:I

—-—>

B BO E
F

ST0 P TOR

MOTIONIO)

AND

DIRECTION (I)

LOCAL

ALL HALT

BRAKE

QUEV

AND

O'RECTION (0)

-—'

SELECTED

3%,

DRAG TORQUE

LEFT
'

LEFT
MOTOR

FULL TORQUE

STOP TOROUE

“”5“

stw MEAS.(1)

TMGI4)

TMG

(4)

MRI-K (4)

DATA 1 (4)

DATA 2(4)

ATA 2(4)

DATA 3(4)

ATA

HEAD

RELAY

NOTE:

ATA 1 (4)

HEAD

3(4)

An arrow signifies a nonstandard DEC signal, such as motor voltage,

head playback, brake voltage, etc.
In the motion control block the arrow above a switch means that pressing this

switch results in tape movement in the indicated direction when the middle
switch is in the LOCAL position.

Figure 2-1

REEL

BRIE?

RIGHT

A33

RIGHT

FULLTOROUE

L__

MOTION (I)
CONTROL

LEFT

DRAG TORQUE

A ND

BRAKE

‘.—_

MOTION

RIGHT

1A NDII

DELAYgO)

REVERSE

:- m
LEI—AV“)

DELAYII)

SELE c TED

DELAY 0)

DECtape Transport TU55 Block Diagram
2-]

The SELECTOR LOGIC block in figure 2—l includes the front panel thumbwheel selector
shown in figure l-l
one

This selector has nine positions (designated 1

of eight select lines

tape control system.

ground.

through 8 and OFF LINE) for selecting

which are the outputs of binary—coded-decimal decoder in the external DECa

During addressing, only one of the eight input select lines is at the asserted

In remote Operation, the SELECT output is asserted negative whenever the thumbwheel setting

corresponds to the asserted address line from the DECtape control system.
Writing is possible on a selected drive only when that drive furnishes control with a WRITE
ENABLE signal at ground.

figure 2-1

is on.

A selected TU55 furnishes such a signal when the WRITE ENABLE switch in

When this switch is set to WRITE LOCK, the output line is negative and writing can-

not take place. If‘the control is commanded to perform a write function when WRITE LOCK is selected,
it diSplays a selection error flag to notify the program of the mistake.

The five motion commands from the external
the left center.

DECtape control system are shown entering at

The ALL HALT signal is asserted negative by the external control whenever the computer

program execution is halted either by the program or by the operator.

computer cannot issue commands to peripheral equipment.

When the program is halted, the

The ALL HALT signal stops those transports

that were in motion at the time of the ALL HALT command, thus preventing a complete run-off of the

tape.

The other four commands, GO,

STOP, FORWARD, and REVERSE, are asserted at ground by

the external control in response to computer program commands.
STOP are complementary levels.

In current DECtape controls, GO and

In the following discussion, the GO,

STOP, FORWARD, and REVERSE

lines referred to are at the output of the signal interface module (BO7).

Tape motion begins at a selected TU55 when the GO line is asserted (STOP must be held
false throughout the desired interval of tape motion). Motion stops whenever the STOP line is asserted
while the GO line is simultaneously held false.
The same conditions as above apply to the FORWARD and REVERSE lines.

For a selected

transport which is set to REMOTE, asserting the FORWARD line (while holding the REVERSE line false)
causes

all subsequent remote GO commands to move tape forward.

Similarly, asserting the REVERSE

line (while holding the FORWARD line false) selects the reverse direction.
reverse

and forward tape-motion switches override the last REMOTE

In LOCAL operation, the

direction command

that the tape

always moves in the direction of the arrow above the switch (see figure 2-1).
Current DECtape controls generate the GO/STOP and the FORWARD/REVERSE signals as

complementary levels.

Forward tape motion, for example, is commanded by assertion levels on GO and

FORWARD accompanied by false levels on STOP and REVERSE.

‘

When forward motion is commanded either locally or remotely, theymotion' control
the FWD output negative.

logic asserts

This signal releases both brakes and applies full clockwise torque to the right

2—2

partial counterclockwise torque to the left motor.

motor and

reel across the head onto the right reel.

As a result the tape moves from the left

The REV line (asserted negative in response to the REVERSE

motion command) applies full torque to the left motor,

partial torque to the right motor, and simulta-

neously releases both brakes. Tape motion, therefore, is from right to left.

At the end of either com-

mand, the STOP line is asserted negative and triggers the stop delay (about 100 msec).

For the

duration of the delay, full torque is applied to the trailing motor and stop torque is applied to the

leading motor (see section 3.3). Thus, for the duration of the delay after the STOP command has
been issued, the motor torques are reversed causing tape movement also to be reversed.

however,

is‘very short and when the delay times out, the motors

their rotation from one direction to the other.

come

This time,

to zero speed while

changing

After the STOP DELAY times out, the tape becomes

motionless and partial torque is applied to both reels to take up the tape slack and the brake is applied
to the motor shaft which was trailing during the previous motion.

The effect of the delay is nullified

if a new motion command is given before the end of the l-sec interval.

Then, the torque signals to the

left and right motor drives are immediately reestablished according to the new motion command.

The

delay starts again at the leading edge of each STOP signal regardless of the frequency of its occurrence;
i.e.,

recovery time is inherent in this type at delay.

An illustration of the tape head is shown in figure 2-2.
associated with their coils.

the coils (to either + or
saturate the tape in
out as four

lines:

—

Every channel consists of two tracks

When writing, the current flows from ground (center tap) through one of

terminal)to saturate the tape in one direction and through the other coil to

the other direction.

ground, +‘,

—,

The coils for the two tracks are wired in series and are brought

and the shield.

Within the head. relay module, the +,

lines (center taps) for a channel are switched by one of five 3—pole,
are

not switched,

Shields

A separate

(also shown in figure 2-2) is brought out to allow measurements of head

skew (or the head perpendicularity).

control).

and ground

normally open reed relays.

but are through-connected from the head to the interface connectors.

line from the timing channel

This line is used only for test purposes (and not by the external

The single head—ground line is used to ground the head case.

2-3

TRACK

TRACK 10

TRACK

-MARK

______s__2

\
__

22 PIN
AMPHENOL
PLUG

TIMING

——-< A

__/I

SHIELD

I»

5—

SKEW
CHECK

CENTER
TAP

—

TIMING

MARK

Figure 2-2

I
I
I
I
I
I
I
I
I
I
I

TRACK

DATA

TRACK 4

TRACK

DATA

TRACK

DATA

TRACK

0(3)

‘4‘

CENTER
TAP

SHIELD

HEAD
GROUND

DATA

DATA 2
DATA

Head Connections

DETAILED DESCRIPTIONS

2.2

This section describes, in detail, the flow of information and control through each of the

Functional elements of the TU55 control unit.

modules as logical operators.

The discussion is limited to describing the various

Detailed descriptions of individual circuits are given in section 2.3,

Module Descriptions.
The basis for the discussion in the remainder of this section is the block schematic in DEC

drawing BS-D-TU55—O—2. This drawing is subdivided into zones bounded by horizontal section A

through D and vertical section I through 8. Circuit locations are referenced by a letter-numeral
combination.

L2 .2 I
.

For other drawing symbology, refer to the

introductory paragraphs of chapter 5.

Interface

All interface signals received or transmitted by the tape motion control circuits are transferred between the TU55 and the external
motion control

DECtape control system.

Interface signals for the tape-

logic consist of: eight unit select input lines, five command input lines, and selected

write enable output control lines.
to the TU55 are made

Bus connections for these signals from the DECtape control system

by plugging a FLIP CHIP cable connector into module receptacles (A5 or A6).

These signals together with the power lines and the information lines (to be described under Read/Write
IHead Circuits) constitute the interface for the entire TU55.

2—4

Unit Select Lines

2.2.2

The eight unit select lines, numbered 1

through 8, are the outputs of a binary-coded-decirnal

decoder in the DECtape control and are supplied to the TU55 for application to the unit selector switch

S5 (A7,

A8).

This manually operated switch establishes the programmed address of the TU55, to allow

the TU55 to be addressed by the computer program.

The unit select lines are connected directly to the

corresponding numbered position contacts of the selector switch.

The switch wiper arm is connected to

input terminal R of the module 807 (C8), thus providing the SELECT command as an output at terminal
Module 307 is either a Type W5l3 Level Amplifier or a Type W990 Blank Module with appropriate

B07.

iumpers, depending upon the type of input signals. As previously explained, when the input levels are
-3v and ground (i.e.,. the control has been designed specifically to drive the solid-state drive), the
W990 Blank Module is used.

When an older type control is used (such as 550, 55l ,

Level Amplifier is used instead to convert relay driving levels to DEC standard levels.

552) the W513
The same applies

also to the command line level.

2.2.3

Command Lines

The four major command lines:
DIRECTIOlN flip-flops (C7,

GO, STOP, FWD, and REV set or clear the MOTION or

C6) based upon programmed commands from the computer.

The ALL HALT command level is generated in the control
when the program is halted.

logic of the computer and occurs

This negative level for assertion clears the MOTION flip-flop (C4) to the

motion(0) state to stop motion of the transport when the computer program halts. Obviously when the
computer program is halted, the computer connot issue commands to peripheral equipment, and so this
action is taken to prevent indefinite running of the transport and to prevent the tape from running off

the reel.

However, to enable the transport to run under local (or manual) mode, theALL HALT level is

AN Ded with the remote level

2.2.4

(C4).

WRITE ENABLE Signal

The TU55 generates the ground level WRITE ENABLE signal for routing to the DECtape con-

trol from terminal board A5,
must
to

pin L.

To assert this level the WRITE

be in the WRITE ENABLE (up) position.

ENABLE/WRITE LOCK switch 53 (A6)

This position enables diode gate VUT of module Bll

(36)

generate the WRITE ENABLE signal, and causes the lighting of the WRITE ENABLE indicator on the

front panel.
For the older type controls, the W513 Level Amplifier circuit serves as a protection diode

‘for the R107 (Bi 1) Inverter.

2-5

2.2.5

Interface Connections
Information lines are brought to the read/write head from the DECtape control system where

they are bussed together for connection to other transports.

Connections to this bus from an individual

TU55 are made by cable connections of module connectors '(A4 and B4).
the Type 6851

These connections are wired to

Relay Module (A4, B4) for connection to the read/write head when the relay is operated

by the (SELECT) signal amplified by solenoid driver ER of the Type W040 Module (B4).

2.2.6

Read/Write Head
A type 6851

Relay Module (A4, B4) establishes connection to the read/write head from the

information bus lines of the DECtape control system.

This module consists of 5 x 3 single-pole,

open contacts which are closed when the relay is energized.

normally

The relay is energized when the TU55 is

selected, thus connecting the read/write head channel coils to the control.

2.2.7

Tape Motion Control

Tape movement and direction of movement are controlled by two Type R202 Flip-Flops; namely,

stop/go MOTION flip-flop (C6) and a reverse/forward DIRECTION flip-flop (C7).
set or cleared

by command signals originating in the DECtape control system or in the reverse tape—motion

and forward tape-motion switches on the front panel (see Figure

2.2.8

The flip-flops are

l-l).

Remote or Programmed Control

The four maior commands that originate in the DECtape control system are GO,

STOP, FOR-

WARD, and REVERSE. Type RI ll Diode Gates (B4, B5, Bé) NAN D—and combine these commands with
the SELECT level within the TU55.

DIRECTION flip-flops.

The output of these gates is used to set and clear the MOTION and

Therefore, motion and direction are controlled only in the selected transport.

The TU55 receives these four maior commands as direct connections from the DECtape control system.
The eight unit select lines,
unit selector switch (A7,

designated 1 through 8., (B8) are connected to appropriate positions of the

A8).

The transport is selected when the selected line coincides with the

position of the unit selector switch.

The negative SELECT level is conditioned by LOCAL and SELECT

ground levels (B7) if the transport is switched to the local mode. Then computer—control selection of
the transport is not affected.

The magnitude of the load on the address line is examined by the external control during

selection to determine whether more than one DECtape transport is being addressed.

2.2.9

Local

(Manual) Control

Switches on the front panel of the TU55 provide for manual control of the tape motion.

The

shift in control from remote to local is performed through the REMOTE/OFF/LOCAL switch 52A (A6).
With the switch on LOCAL, the selected level

external command NAND gates (RI I Is).

(C7) is forced to ground potential thus inhibiting the

Inhibiting; these gates prevents commands from the DECtape

control system from affecting the state of either the MOTION or DIRECTION flip-flops and thus prevents interference with manual

control.

REVERSE S4 (A5) and FORWARD SI

With switch 52 on LOCAL, +IOv is supplied to both the

(A7) switches.

This condition permits the switch operation to es-

tablish the appropriate state of both the MOTION and DIRECTION flip-flops when pressed.

Switches

SI and 54 are of the momentary contact type which return to a reset position when released.

When the

REVERSE switch is pressed, the MOTION flip—flop is set to the motion(l) state and the DIRECTION

flip-flop is set to the direction(0) state by grounding the appropriate output connection terminals of the

flip-flops.

The grounding of the flip—flop outputs is done via the outputs of the W70l Switch Filter,

generally used to interface switch action to the logic (refer to the circuit description).

This module is

used both to filter out switch contact bouncing and to load the some contact with some current from a

sufficiently high potential to positively bridge across any insulating film that might be formed over the
switch contacts, thus assuring an electrical contact when the switch is pressed.
Under these conditions the tape moves in reverse.

When the FORWARD switch is pressed,

'the MOTION flip-flop is set to motion(I) and the DIRECTION flip-flop is set to direction(I),
the tape forward.

Release of either the REVERSE or FORWARD switch clears the MOTION flip-flop,

thus stopping tape motion.

Therefore, tape motion under manual control occurs only as long as the

REVERSE or FORWARD switch is held down physically.
switches provides a protection feature,
direction will

2.2. IO

moving

Inter—wiring between the REVERSE and FORWARD

that if both switches are pressed simultaneously, the FORWARD

prevail.

Motor Control
The two motors which move the tape past the read/write head are operated by ac power which

is controlled separately for each motor by an SCR switch on a Type G850 SCR Motor Control Module

(D4, C4).

These SCR circuits, in turn,

and DIRECTION flip-flops.

are

controlled by combinations of the states of both the MOTION

A brake on the shaft of each motor is also individually controlled by com—

binations of the state of these control flip—flops (C7, C6).

The states of the control flip—flops are

decoded by RI II NAND gates which control the SCR circuits, and by Type W040 Solenoid Driver

Modules(D4, C4) which control the brakes. Table 2-I indicates the assertion levels (I) which operate
the motors and brakes; or indicates the nonassertion levels (0) which do not operate these devices for

all combinations of control flip-flop conditions.
2-7

Table 2-l also presents the three states of motor and brake operation when the tape is

running in either the Forward or reverse direction.
The Functions of the Type G850 SCR Motor Driver Modules (D4,

C4) are as follows:

with a

negative assertion level at terminal H, the motor is driven at full torque; with a negative assertion level
at terminal

F, the motor is driven with enough drag torque to take up slack in the tape when the'motor

functions as a trailing motor; with a negative assertion level at terminal E, the motor has iust enough

torque to take up slack in the STOP condition.
When the tape is running in the forward direction, full torque is applied to the right motor
and drag torque is applied to the left motor.

When the STOP command is given, full torque is removed

from the right motor and applied to the left motor for the duration of the delay of the Type R303 One

Shot Module (D7), and stop torque is applied to both motors.

At the end of the one-shot delay, which

is approximately 100 msec, full torque is removed from the left motor, the brake is applied to the left

motor, and stop torque remains on both motors to take up the slack in the tape until the next command
is received.

(Of course the stop torque applied to that motor which has the brake on is doing nothing).

A similar sequence of events occurs when tape movement is in the reverse direction
STOP command is received.

shaft of the trailing motor,

and the

Hence, after a STOP command occurs, the brake is applied only to the

positively stopping the motor shaft to which it is applied.

When the tape

is at rest (which is most of the time), the stop torque applied to the motor to take up tape slack is
minimum to avoid excessive heating of the system.

The logical

negative levels applied to pins E, F, and H of the G850 SCR Motor Control are

ANDed with the negative BRAKE ENABLE level

(C4, D4).

This level is negative (Bé) only when the

REMOTE/OFF/LOCAL switch is on either REMOTE or LOCAL.

When the switch is in the OFF position,

the level is at ground potential and disables both the G850 SCR Motor Control motor circuits and the

brakes (dc HO and —l5v are still present).

This switch position is used when a tape reel is to be

mounted or dismounted and is also recommended when a particular drive is not being used.

older Type TU55

Transports the same 3-position switch was used to interrupt the

port and the BRAKE ENABLE level did not condition the G850 circuit.

(On the

power to the trans-

Thus the power itself was

interrupted instead of logically controlling the (3850 Motor Control.)

2.2.] 1

Transport Selected Signal
The negative SELECT level enables another Relay Driver Type W040 (C7) whose output is

:sent through a resistor to

interface pin K on A5/A6 modules from where it is sent to the control.

control can use this line to sense whether more than one transport is being selected at one time.
an

The

Usually

analog type circuit uses the fact that current could go through the resistor when the relay (transport)

is selected,

and, if more than one (or no) transport is selected, causes an error signal.

not needed when the transport is connected to a 550,

2-8

551, or 552 Control.

This feature is

Transformer Tl ((C3) synchronizes the SCR firing with the 60—cycle waveform of the primary
power.

The Thyractor connected across the primary of this transformer protects the diode bridge rectifiers

in the Type G850 Modules.

Motor and Brake Operation Truth Table

Table 2-l

Control Element

Left Motor

STATES

Operation

Reverse

Forward

2.3

Mode

Direction Motion

Right Motor
Pin E

Left

Pin H

Stop
Delay Torque Torque Torque

Brake

Full

Pin H

Pin F

Full

Drag

Pin F

Pin E

Drag
Stop
Torque Torque Torque

Right
Brake

Running

Off

Stopping

Off

Stopped

Off

Running

Off

Stopping

Off

Stopped

Off

MODULE DESCRIPTIONS

Complete circuit information for the FLIP CHIP modules in the Type TU55 DECtape Transport
is

contained in the replacement schematic engineering drawings (see chapter 5). A list of the FLIP CHIP

modules used in the TU55 is included in engineering drawing PL—TU55—O-5, Module count list.
locations are shown on drawing MU—TU55-O-5.

These modules are described in DEC

Module Catalog, C-IO5, and in appropriate New Module News Bulletins.

Their

Digital FLIP CHIP

Descriptions of non-catalog

modules are contained in the following subsections.

2.3.1.

Type R303 Integrating One Shot (Delay)
This module includes a zero-recoveryv-time multivibrator and complementary output buffers

(see Figure 2-3 and DEC drawing RS-B—R303).
at any time either within or outside the delay

It responds to inputs signals (up to 2 mc) which may occur

interval

postpone the delay indefinitely.

2—9

Successive inputs above a preset frequency can

ENABLE
GATE

PULSE

INPUT

OUTPUT
D
CLOCK

EXTERNAL

RHEOSTAT l

13TH

,._a_..__-.‘

7—"

JUMPER

INTERNAL
RHEOSTAT

FOR

400NSEC

PULSES

_ ,_x_.
EXTERNAL
CAPACITOR

R401

VARIABLE CLOCK

Figure 2-3 Diagram of R303 Integrating One-Shot

2.3.2

Type W513 Level Amplifier
This module contains six identical level amplifier circuits (see engineering drawing

W5l3).
are

RS-B-

The input levels are received from DEC relay or solenoid driver circuits having outputs which

between —2 and —3v when the driver is “on”(i) and are Floating when it is "off“(O).

current exceeding 1 .2 ma to the
asserts the output at

input

level amplifier makes the input potential more positive than —3.5v and

ground. When the input current is cut off, the input potential returns to approxi—

mately —5v and the output becomes —3v.

Since all circuits are identical, the first circuit in the re-

placement schematic (input at D and output at E) is described.
The circuit is quiescent when no input current is flowing into D.

input return R1 at about -5v.

Diodes Di and D2 clamp

The drop across Di maintains Ql cutoff, thus allowing R3 to keep the

Q2 base positive and cut off Q2.

D4 clamps output E at the Q2 collector to —3v.

When the input goes more positive to —2 to ~3v it startssupplying current to pin D.

back bias Di and turn on Ql

Q2 base current flows through Qi and R2 so Q2 turns on,

It will

bringing E to

ground potential. When the input current at D opens, both transistors cut off again and the circuit is

quiescent again.
A resistor is tied to pin T.

It is used to simulate relay currents such as those existing in the

555 Relay TranSport and therefore allows mixing TU55s and 555s in the same system.

The current

through this resistor is measured by an analog circuit at the control to determine whether one or more
transports are being selected and causes an alarm or error signal in case the latter condition happens.

Type G850 SCR Motor Driver

2.3.3

Essentially this module is an SCR switch for the ac voltage supplied to any one of the drive
motors of the TU55.

The SCR switch is turned on and off twice during each cycle of the ac power. The

firing point of the SCR is controlled so that it can occur at almost any point along the sinusoidal waveform of the ac power; thus controlling the amount of energy that is transmitted to the load (the motor),
and thus achieving control of motor torque.

A simplified schematic diagram of this module‘ is shown in

Figure 2-4, a complete schematic in DEC engineering drawing RS-B-G850.

Anovu)

*3/37,

:Pana

(3 GND 0—4»

[MPAIES

FULL.

DRAG-

STOPPEMG.

TORQUE

u
SYNC

Ac LINE

|
I

2:
—

_____

I
1

L-

______

XFMR

'
|

LOAD

FofifiA
us
TERMINALS

B-:——BO-

l
I

Ac LINE

LNof part of 0850 Schematlc

'22:.

I
Dl5
J

Infizmua

one

;———______T

cam

Figure 2-4

Schematic of (3850 SCR Motor Driver

The SCR itself (D15), is connected into a diode bridge so that current always passes though it
in the same direction

(an SCR is not a bilateral device). The firing circuit for the SCR incorporates a

uniiunction transistor (Q4) and an RC timing network. The capacitor (Cl) in this network starts to charge
at the

beginning of each half cycle of the ac voltage

When the voltage developed across the capacitor

reaches the firing point of Q4, conduction starts and current flows in the primary of a coupling transformer (Tl).
to operate

Voltage induced in the secondary of Ti controls the firing of the SCR and causes the motor

Three input timing circuits determine the trigger timing of the SCR.
the two—diode

input of these circuits

cause

A —3V level applied to

the SCR to trigger at a fixed rate or a variable rate determined

by the setting of potentiometers R5 and R9. The fixed input circuit (Q3) triggers the SCR near the
beginning of the sinusoidal wave to produce maximum torque.
A low voltage ac input is supplied to terminals U and V from the secondary at transformer Tl

of the TU55 logic (not Tl of the module).

This input voltage is full wave rectified and is clipped by a

Zener diode, but is not filtered.

charge

It provides the potential toward which the timing circuit attempts to

Being a stepped down version of the primary ac power which operates the drive motors, this

voltage synchronizes the firing of the SCR to the line Frequency.

Since the voltage at the end of each

half cycle is zero, the RC network must start charging at the end of each half cycle.

Therefore, this

pulsating voltage causes the SCR to fire each half cycle at a point in time measured from the zero
voltage point.

CAUTION
Be very careful when handling this circuit or probing it for measurement
purposes since it contains ll5v ac. A short circuit caused by a probe
Do not tamper with this module without

could produce a high current.

first disconnecting power from the back terminal.

2-12

CHAPTER 3

OPERATIO N

INTRODUCTION

3.]

As stated in chapter I, the TU55 can be operated in either a local

Local operation is accomplished by use of the controls and indicators on the

matic—programmed) mode.

front panel of the equipment.

Remote operation is effected through programmed commands produced by

the stored program of the computer.
modes of operation

3.2

(manual) or a remote (auto—

The following paragraphs contain information applicable to both

CONTROLS AND INDICATORS

The functions of the controls and indicators on the control panel in figure 1-] are summarized
in table 3-l

paragraph

3.2.1

Additional information of the action initiated by the controls is given in the following

Operating Notes
When the REMOTE/OFF/LOCAL switch is in the OFF position, the REMOTE indicator does

light but the TU55 logic still responds to selection, control, and command signals from external con-

not

trol.

Consequently the external control may select and attempt to read or write tape but no tape motion

takes place.
no

In all normal

modes, this condition idles both the DECtape control system and TU55 because

timing channel signal is made available from a motionless tape.

When the system is commanded to

write on the timing and mark channels, the timing pulses are generated within the external control per-

mitting the control to operate as if tape motion were available.

3 .3

LOADING TAPE
To mount a reel of DECtape on the TU55 after energizing the equipment,

proceed as follows

(see figure l-l and table 2-1):
To load tape set the REMOTE/OFF/LOCAL switch to the OFF position.
and inhibits the operation of the G850 SCR Motor Driver circuits.

unloaded with tape reels.

This releases the brake

Then the hubs are free to be loaded or

If a new reel is to be mounted, unreel about a foot of tape from it over the

guides and read/write head and 'wind the tape one or two revolutions onto the right reel. Turn the switch
to

either LOCAL or REMOTE as is desired for the next operation

3—I

TABLE 3-]

FUNCTIONS OF CONTROLS AND INDICATORS

Control or Indicator

(designated in
pointing to the left)

Reverse tape-motion switch

figure

l-l

arrow

Function

Provides reverse tape motion (i .e., from right to left)

only if REMOTE/OFF/LOCAL switch is on LOCAL.

WRITE ENABLED/WRITE LOCK switch
WRITE ENABLED

Permits external DECtape control system to write information on the TU55.

WRITE LOCK

Prevents the above writing.

If external DECtape con—

trol system is commanded to write on tape during the
WRITE LOCK setting, the control initiates a selection
error

flag to notify the program.

The WRITE LOCK setting, however, does not prevent
tape motion when the REMOTE/OFF/LOCAL switch
is on REMOTE

WRITE ENABLED indicator

Lights when WRITE ENABLE/WRITE lock switch is in
the WRITE ENABLE position.

Address selector (or unit selector)

When set to one of the numerals (designating addresses)

0)\l0~U1-P~OJN—‘
OFF LINE

and REMOTE/OFF/LOCAL switch is on REMOTE or

OFF, the transport is selected when the line indicated
by the switch wiper corresponds to the computer selection through the DECtape control.

Then the trans-

port responds to command signals from external control
and can assert a write enabling signal to the control.
In addition, all head channels are connected through

the head relay to control bus information lines.
Prevents external DEC control system from selecting

the TU55

REMOTE/OFF/LOCAL switch
REMOTE

Permits TU55 to accept command and control
from the external

signals
DECtape control system; also enables

head relay logic to connect all head channels to con-

trol bus information lines as soon as appropriate transport is selected.
OFF

Inhibits operation of the G850 SCR Motor Control
Modules and releases the brakes. Power for the logic

components comes from power supplies associated with
the external control, and therefore the OFF position
does not turn off the +10 and -l5v power. The OFF
position is used when loading new tape reels since it
releases the motor hubs. The transport should be set
to

OFF when not in use.

3-2

TABLE 3—]

FUNCTIONS OF CONTROLS AND INDICATORS (continued)

Control or Indicator

LOCAL

Function

Permits Forward and reverse tape-motion switch to

provide tape motion in direction oF arrow. Transport
cannot

be selected.

REMOTE indicator

Lights only when transport is selected by the control.

Forward tape-motion switch (designated

Provides For motion in the Forward direction (i .e. ,

in Figure l-l

right)

by arrow pointing to the

From leFt to right), but only when REMOTE/OFF/

LOCAL switch is on LOCAL.

IF looth reverse and

Forward tape-motion switches are pressed simulta-

neously, the Forward motion takes place.

CHAPTER4

MAINTENANCE

4.]

EQUIPMENT REQUIRED
Maintenance activities servicing TU55 DECtape Transports require the equipment listed in

table 4-1, or the equivalent; plus standard hand tools,

TABLE 4—]

cleansers, test cables, probes, etc.

RECOMMENDED MAINTENANCE EQUIPMENT

Multimeter

Oscilloscope

Model

Manufacturer

Equipment

630-MA or 260

Triplett or Simpson
*

Tektronix

Series 540 or 580
with Type CA differ-

ential preamplifier
FLIP CHIP module

DEC

W980

extender

Small thin-bladed
screwdriver

All four standard

Phillips-head
screwdrivers

sizes
I

Allen-wrench set

No. 667

Head gain and head skew tests require a dual-beam oscilloscope such as Tektronix Type 550 or 551
with a high-gain differential preamplifier for each beam channel, such as Tektronix Type D. However,
these tests are seldom necessary in the field.

4.2

PREVENTIVE MAINTENANCE

The following weekly and monthly preventive maintenance schedules are recommended to

forestall possible failures.

Special emphasis is placed on cleanliness of tape handling surfaces because

dust and oxide particles contribute to read errors.

4.2.1

Weekly Schedule
a.

Clean entire front panel of tape deck.

Clean both surfaces of tape guides and tape head using an appropriate head cleaner

and a soft lint—free cloth.
c.

Check proper operation of motor and reel brakes before loading tape by momentarily

pushing forward and reverse tape-motion switches on front panel.
4-]

4.2.2

Monthly Schedule
This schedule should be performed on each DECtape once a month when equipment operates

on a

standard 8-hour shift and more often when daily operation exceeds one shift.

outs on

Stagger the check-

individual transports evenly throughout each month.
a.

Clean the exterior and interior of the cabinet using a vacuum cleaner and clean cloths

moistened, if necessary, in nonflammable solvent.
b.

Clean air filters at the bottom of bay using procedure given in PM section of maintenance

manual for DECtape control system.
c.

Lubricate door hinges, casters, etc., with a light machine oil.

Inspect equipment for completeness and general condition. Repaint scratched or corroded

areas.

Make sure each FLIP CHIP module is securely seated in its mounting panel connector.

Run a complete exercise and diagnostic routine for each transport so that both the trans-

port and its associated control are exercised in all possible modes and in both directions.
Maintenance programs for this purpose are available from DEC for all computer/control/

transport DECtape systems.

Applicable programs are listed in the maintenance manual for

the DECtape control system.

Log all errors to provide a malfunction history as an aid to

troubleshooting.

If tape is slack or bounces during exercises,

perform the adjustment and

calibration procedures in the next subsection.
9.
to

Rotate tapes among all transports and use the read routines of the maintenance programs

be sure that all tranSports can read tapes generated by other transports.

If each transport

operated satisfactorilyin step f, any malfunctions in this step are probably due to head skew.
Head skew can be measured by the procedures given later in the troubleshooting subsection

but cannot be adiusted in the field.

4.3

TAPE TENSION AND TRANSPORT STOP ADJUSTMENT
a.

Set the R303 Integrating Delay to about 70 ns.

Pin D in A04 of the delay is varied

with the aid of the trimpot mounted on the module.
Initiation of the delay is made by pressing momentarily on either the forward or reverse

switch when the REMOTE/OFF/LOCAL switch is on LOCAL.
this operation

4-2

No tape reel is needed for

Mount a tape reel on the transport.

ment.

Press the forward switch and watch the tape move-

The trailing torque of the left motor should be adiusted on the (3850 Module All

trimpot (as shown in Figure 4-l ).
the tape; and if too little,

If the torque is too great it will

impede the movement at

flapping or loose contact with the read write head will result.

The technician who maintains the

equipment might develop a ”touch" so that by pressing

his Finger over the tape at the trailing reel he can tell if the tape is too tight or loose,

simply by the stiffness of the tape while in motion.
c.

Repeat same procedure for reverse tape movement by pressing reverse switch.

This

time the pot adjustment is done on module A12.

Press forward switch for a second or two and release it; the tape action while stopping

should be smooth.

disappears.

If bouncing occurs, increase the stopping torque until bounce iust

This stop torque is maintained when the transport is not operating (which is

most of the time) and excessive torque merely

the whole equipment.

results in overheating the motor and hence

Torque adiustment is made on the appropriate pot (figure 4-l) on

module A12.
(3.

Repeat same procedure when pressing the reverse switch, watching for the stop when

tape movement is in reverse.

Adiust pot on module Al l

POT FOR
DRAG TORQUE

(OR AT REST)

ADJUSTMENTS

POT FOR STOP

\ /
_

L_L———

6250 MODULE

Figure 4-l

4.4

Module Adjustment Trimpots

lHEAD OUTPUT CHECK
This check is used to determine whether the read-head is developing the proper read signals.

If the read-head performance is not satisfactory, the head should be replaced.

4-3

No attempt should be

made in the field to repair or even change head position by loosening the brackets that hold it to the

plate. Although DEC personnel are authorized to replace heads in the field, the replacement involves
realignment and usually requires the return of the transport to DEC, Maynard.

The following diagnostic

procedure can be performed with any single-channel oscilloscope having a high-gain differential pre—

amplifier capable of handling signals in the millivolt range over a bandwidth of 0 to 60 kc, (Tektronix
Type D Plug-in Unit).
a.

Move tape manually in a forward

Mount a DEC certified tape on the TU55 Transport.

direction until approximately one half of the tape is on each reel.

Disconnect the 22-pin Amphenol head connector from rear of Head-Relay Module C3851

located at the extreme right of the mounting panel seen from the rear.

Attach the two probes

of the differential amplifier to pins B and C of this connector and attach the ground clip to

Set the oscilloscope to sync

internal, and set the vertical preamplifier to 5 mv/cm

(0.5 mv/cm if an XlO probe is used).
An alternative method is to cause a closure of the information relays by grounding (with the
aid of a clip) pin E of the G851 Module at location ABl

This eliminates disconnecting the

plug procedure, as outlined above, by making it possible to monitor the same plug points on
the wiring panel front.

socket ABl
c.

The probes are now attached to pins AF and AH of the same FLIP CHIP

The gound clip is attached to pin C.

Move tape forward and reverse using forward tape-motion switch and observe that the

read-head waveform is about 10 to 12 mv peak-to-peak.
cl.

Repeat step c,attaching the probes to pins F-H, P-R, U-V, and Y-Z. These signals may

not

look sinusoidal (as they do for pins B-C), but the peak—to-peak amplitude should measure

the same as in
now are:

step'c.

The same alternative exists here as in step b.

The pin pairs to monitor

AN-AP, AV-BD, BH-BJ, and BN-BP.

HEAD-S KEW CHEC K

Although the head-skew is not adiustable in the field, the following check should be performed
when unusual numbers of read errors are observed on an individual transport engaged in reading tapes

generated by several other transports. The procedure requires a dual-beam oscilloscope with two high-4
gain differential preamplifiers for each scope-channel (as outlined in the equipment needed,4.l).
0.

Write a timing track on a scratch tape using one of the DECtape utility routines.

Rewind tape back onto the left reel.

Dismount the left reel from the left hub and mount

it on the right and mount the empty reel on the left hub.

the left reel.

Thread tape over the head and onto

Move tape in reverse to fill up the left reel.

The tape is now with its oxide

facing up away from the head.
c.

Disconnect the 22-pin Amphenol head connector from rear of Head Relay Module G851

This module is located at the extreme right of the mounting panels, seen from the rear.
dl.

Connect the two upper-scope channel probes to head connector pins A and C and their

ground clips to the chassis. Connect the two lower-scope channel probes to head connector
Set both channel preamps to A-B (the

pins A and D and their ground clips to‘the chassis.
differential setting).
e.

Move tape forward by using the forward tape—motion switch.

that each waveform has the same peak-to-peak voltage.
a

Adiust channel gain so

Sync on the upper beam and take

reading of the phase difference between‘the signal peak at pins A and D (track IO) with

respect to the signal peak at pins A and C (track I).
I0 signal leads or lags the other and the amount.

the tape length as possible.

Be sure to record whether the track

Make all readings as near the center of

Skew readings greater than 5 psec indicate possible incompati-

bility among transports. Probably the head has become misaligned through physical damage.
Then the transport must be returned to DEC,
f.

Remove all

Maynard, for realignment.

probes, reconnect the Amphenol connector to the rear of the (3851 Head

Relay Module, and rewind the tape to the original state.
NOTE I:

It is possible here also to use the alternative method of monitoring

the channel waveforms (see alternate method, section 4.4b) by energizing
the relay at the G851 Module by grounding pin E.
can

By doing so probe clips
The pins are D-H

be attached to the wiring panel pins at location AI

for one probe and D—J for the other.

NOTE 2: In some heads (manufacturer, GJM) use pin F instead of pin H on
the FLIP CHIP socket. On the Amphenol plug at the back use pin B instead
of pin C.

4.6

WRITE ENABLE CIRCUIT CHECK
a.

Set the WRITE ENABLE/WRITE LOCK switch to WRITE position and check that the WRITE

ENABLE indicator lights.

Also check that a ground level is present at terminals A5L and

A6L (C8).

4'15

Set the switch to the WRITE LOCK position and check that the WRITE ENABLE indicator

is extinguished.

Also, check that level at terminals A5L and A6L is -3v. Check transmission

of this level from terminal A5L to the DECtape control system.

TROUBLESHOOTING

4.7

The forward and reverse tape—motion switches on the front panel of the TU55 are useful in

checking the operation of the unit and in assuring that the tape—motion mechanism is working properly.
It is suggested that the first step in troubleshooting should be a check of the modular logic circuits.

For this check, the primary ac power cable should be disconnected from the plug at the back

of the transport to prevent movement of the tape drive motors.
the LOCAL position.

appropriate switch.
motor shaft

Set the REMOTE/OFF/LOCAL switch to

Then simulate the commands to GO FORWARD and GO REVERSE by pressing the
When the switch is released, the STOP command is initiated to energize the left

brake (the brake coil is energized from the —l5v supply).

Under these conditions,

use an

oscilloscope or a voltmeter to compare the command signals throughout the logic circuits against those
in table 3-].

This operation is checked by monitoring the terminals of the Type G850 Modules (All and

A12) and the Type W040 Modules (B12) with an oscilloscope of voltmeter to verify proper signal levels
for all operating conditions of the MOTION and DIRECT ION flip-flops (BO8).

hubs to check for proper operation of the brakes.

Then inspect the motor

This is accomplished by assuring that the proper hub

stops when called upon to do so by the command logic (activated by operation of the front panel tapemotion switches).

If the truth table cannot be verified, continue troubleshooting by signal

tracing, monitoring

the signal levels at different NAND gate inputs and outputs and working back toward the control

flops until the cause of the malfunction is found.
ac

flip—

If the truth table can be verified, restore the primary

input power, install a reel of tape on the drive mechanism, and repeat the truth table verification

procedure for proper tape movement and end stopping.

If the malfunction still exists, check the

following sources of trouble:
a.

Transformer Tl

secondary is not presenting stepped down ac power to terminals U and V

of the modules All and A12 (the Type G850 SCR Motor Driver Modules).

Type 0850 Modules are defective.

Electromechanical system (e.g. reel motor) rather than the control logic.

4-6

RECOMMENDED SPARES

4.8

Table 4-2 lists the recommended spare parts for TU55 Transport systems.
in the TU55 may be replaced by an S-series module with the same number.

A R-series module

All items are available at

DEC, Maynard, but may be ordered from the other firms listed.

TABLE 4—2

RECOMMENDED SPARE PARTS

Part

Number

Manufacturer

Part

G850

SCR motor driver

DEC

0851

Head

DEC

R002*

Diode network

DEC

R303‘**

Integrating one shot

DEC

5107*

Inverter

DEC

Diode gate

DEC

5202*

Dual

DEC

W040

Solenoid driver

SI 1 I

relay

flip—flop

DEC
'

DEC

W5l3***

Level

W70ll

Input network

DEC

Rotary selector switch (address selector)

DEC

Rocker switch (REMOTE/OFF/LOCAL)

Cutler-Hammer

Rocker switch (WRITE ENABLED/LOCK)

Cutler—Hammer

Rocker switch (Forward and reverse tape-.
motion) (with off—nonmomentary on circuit)

Cutler-Hammer

GéV52

7533-7

Capacitor (reel motor), 7 mfd, 300 wvdc

Sangamo

MOT-l

Torque motor, 70-frame, SP spec

MD/BS70—
0-] I -I—A
8132K20

amplifier

GéV52
8132K22
GéV52
8137K21

Electric Indicator
Co.

BK-OOOI

(ELINCO)

Megatrol

Friction brake, FB—l8l-23

DEC spec
These modules are contained in the basic PDP-8 or the TCOl DECtape Control,
parts are not required if the TU55 is part of this system configuration.
*

This module is contained in the TCOI ,

so a

duplicate spare

dupllicate is not required if the TU55 is used with a TCOI

’

DECtape Control.
***

This module is required only if the TU55 is not used with a TCOI

4-7

DECtape Control.

CHAPTER5
ENGINEERING

5 .I

DRAWINGS

INTRODUCTION
This section contains reduced copies of the engineering drawings,

(see Pertinent Documents

chapter I) required for understanding and maintaining the Type TU55 DECtape Transport.
are

in addition to the complete set of full-size drawings Forwarded with each TU55.

These drawings

Only the full size

drawings should be used by maintenance personnel for work on the units. The full-size drawings show
variations peculiar to an individual installation.

5 .2

CIRCUIT SYMBOLS

The block schematics of DEC equipment are multipurpose drawings that combine signal flow,

logical Function, circuit type and physical location, wiring, and other pertinent information. Individual
circuits are shown in block or semiblock form,

using special symbols that define the circuit operation.

These symbols are similar to those apped‘ring in the FLIP CHIP Module Catalog but are often simplified.

Figure 5-l illustrates symbols used in DEC engineering drawings.

5 .3

LOGIC SIGNAL SYMBOLS
DEC standard logic signal symbols are shown at the input of most circuits to specify the enabling

conditions required to produce a desired output.
or

These symbols represent either standard DEC

logic levels

standard FLIP CHIP pulses.

5.3.l

Logic Levels
The standard DEC

logic level is either at ground (0 to —0.3v) or at -3v (-2.5 to

—

3.5V)

Logic signals generally have mnemonic names which indicate the condition represented by assertion of the

signal.

An open diamond (—[>

-) indicates that the signal is a DEC logic level and that ground represents

assertion; a solid diamond (-—+ ) indicates that the signal is also a DEC logic level and that
sents assertion.

must

All

—

3v repre-

logic signals applied to the conditioning level inputs of diode-capacitor-diode gates

be present for a minimum of 400 nsec before an input pulse will trigger operation of the gate.

5.3.2

ELIP CHIP Pulses
Two types of pulses, R series and B series,

produced by R-series modules starts at

—

are

used in FLIP CHIP circuit operation

The pulse

3v, goes to ground (— 0.2v) for TOO nsec, then returns to

This pulse is shown in figure 5-2.
5'-l

—

3v.

NON- STANDARD

SIGNAL

-———-———>

-———————-—-—{>

GROUND LEVEL PULSE

——-+

NEGATIVE PULSE

———————-—<>

GROUND LEVEL

——————.

NEGATIVE LEVEL

LEVEL TRANSITION USED As A PULSE
OR TRIGGERING ON THE LEADING EDGE
OF A GROUND LEVEL

———————<>(>

TRIGGERING ON
OF A PULSE

__________»

o—«Mr—

TRAILING EDGE

-15V LOAD RESISTOR CLAMPED AT -3v

PNP

TRANSISTOR

INVERTER

1. BASE

THE

‘

2. COLLECTOR

3. EMITTER

.__

GROUND-LEVEL NAND. NEGATIVE-LEVEL

__..

~/\

NOR DIODE GATE

GROUND-LEVEL NOR, NEGATIVE—LEVEL
NAND DIODE GATE

—o

—<>

—

Figure 5-]

DEC Symbols
5-2

CAPACITOR-DIODE GATE, POSITIVE OR NEGATIVE
INDICATED BY POLARITY OF THE INPUTS.
I. PULSE INPUT
2. CONDITIONING LEVEL INPUT

3. PULSE OUTPUT
2

DIODE—CAPACITOR-DIODE
GATE

CAPACITOR— DIODE

‘

GATE

PULSE INVERTER

PULSE AMPLIFIER
I. PULSE INPUT, POLARITY INDICATED
BY INPUT SIGNAL
2,3. TRANSFORMER -COUPLED PULSE
OUTPUT. EITHER TERMINAL MAY
BE GROUNDED

——02
PA
—-03

FLIP-FLOP (MOST FLIP-FLOPS HAVE ONLY SOME
OF THE FOLLOWING):
DIRECT- CLEAR INPUT
.

mqmu¢g~_

1—."

GATED-CLEAR INPUT
DIRECT-SET INPUT

GATED-SET INPUT
COMPLEMENT INPUT
OUTPUT LEVEL,-3V IF 0,0V IF I
OUTPUT LEVEL, 0V IF 0, -3V IF I
CARRY PULSE OUTPUT. UPON BEING CLEARED
.

DELAY (ONE-SHOT MULTIVIBRATORI
I. INPUT PULSE
2. OUTPUT LEVEL,-3V DURING DELAY
3,4. TRANSFORMER-COUPLED PULSE
OUTPUT. EITHER TERMINAL MAY
BE GROUNDED

DLY
—o4

Figure 5-1

DEC Symbols (continued)

5...3

t--- mousse—1

__.1

Figure 5-2

L—a'oousec
I

FLIP CHIP R-Series Pulse

The B-series negative pulse is 2.5V in amplitude and 40 nsec in width as shown in Figure 5-3.
IF this pulse is applied to the base of an inverter, the inverter output will be a narrow pulse, similar in

The B-series positive pulse, which goes from ground to +2.5v, is

shape to the R-series standard pulse.

the inverse of the B-series negative pulse.
OVERSHOOT

—

GND

—2.5v

—~

—

—-

PULSE

p-WIDTH +1

Figure 5—3
5.4

FLIP CHIP B-Series Pulse

SEMICONDUCTOR SUBSTITUTION
Standard EIA components as specified in table 5—]

modules of the TU55 DECtape Transport.

TABLE 5—]

DEC

can

replace most DEC semiconductors used in

Exact replacement is recommended for semiconductors not listed.

SEMICONDUCTOR SUBSTITUTION
EIA

DEC

EIA

D662

IN645

DEC 3638

2N3638

D664

1 N3606

DEC 3639, -0

2N3639

DEC 3009

2N3009

DEC 3790

2N3790

DEC 3494

2N3494

MR2066

lN4003

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PARTS LIST

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