Atari 810 Field Service Manual

ATARI 810 DISK DRIVE

FIELD SERVICE MANUAL

□JULY 1980
FS015854
REV.1

I

II

TABLE OF CONTENTS

1. SPECIFICATIONS 1-1

2. THEORY OF OPERATION 2-1

3. BLOCK DIAGRAMS & SCHEMATICS 3-1

4. FLOPPY QUICKCHECK 4-1

5. TROUBLESHOOTING GUIDE 5-1

6. DISSASSEMBLY/REASSEMBLY 6-1

7. ADJUSTMENTS 7-1

8. PARTS LISTS 8-1

9. APPENDIX 9-1

10. INDEX 10-1

III

SPECIFICATIONS

1-1

TECHNICAL SPECIFICATIONS

1. Uses ANSI standard 5¼ inch diskettes in a

soft sectored format.

2. 40 tracks at 48 TPI track density.

3. Single density (FM), single sided

recording.

4. Over 90K bytes storage per diskette.

5. 709 sectors of 128 bytes each.

6. Minimum data access time: 236 milliseconds.

7. Average data transfer rate: 6000 bits per

second.

8. Automatic stand-by capability (built in

microprocessor).

9. Up to four Drives can be daisy chained to a

single 400/800 Computer Console (w/minimum

16K RAM) via select switches at the rear of

the Drive.

10. Drives directly interface with the ATARI

400/800 Computer Console (16K RAM) or

indirectly through the ATARI 850 Interface

Module or 820 Printer.

1-2

THEORY OF OPERATION

2-1

THEORY OF OPERATION

HEAD

DISKETTE

The ATARI 400/800 Computer Console with 16K of RAM
installed connects directly to the 810 Floppy Disk
Drive. The Drive may also be daisy chained through
the 820 Printer or the 850 Interface Module. Up to
four Disk Drives can be connected to a single
Console.
Refer to the Disk Drive Operators Manual for
installation and operating instructions.

STEPPER

LOGIC AND

MOTOR

READ, WRITE

AND ERASE

DISKETTE

DRIVE LOGIC

AND MOTOR

400/800

COMPUTER

CONSOLE

TRANSFORMER

DATA

INPUT/OUTPUT

MANIPULATION

AND

POWER

SUPPLY

ATARI 810 FLOPPY

DATA

INTERFACE

DISK DRIVE

2-2

The ATARI 810 Floppy Disk Drive consists of the
following major sections:

• Data Input/Output and Manipulation

• Data Interface

• Read/Write and Erase Heads

• Stepper Motor and Logic

• Diskette Drive Motor and Logic

• Power supply

DATA INPUT/OUTPUT AND MANIPULATION SECTION

Data Input/Output and Manipulation Section

2-3

Data, control commands and a VCC/RDY signal from the
Computer Console enter the Disk Drive through either
of the two serial I/O connector jacks at the rear of
the Drive chassis.
Each of the three main signal input lines are
buffered for static protection and to reduce power
consumption on the 800 I/O lines.
Data is sent by the Console in serial format, with
checksums accompanying the data for validity
verification.

The Drive’s PIA is primarily a buffering and signal
formatting device, with no decision making or
computational capability. It is responsible for the
following:

• Applying the Console’s serial outputs to the Data

2nd Address Busses when requested by the Drive’s
Microprocessor Unit (NW).

• Assisting in the control of the Read/Write and

Erase head position by buffering commands sent to
the Stepper Motor Logic.

• Assisting in control of the Diskette Drive Motor

Logic.

• Providing 128 bytes of RAM for temporary storage

of status information and data sent by the Data
Interface Section for application to the MPU.

The MPU provides the primary decision making and
computational capabilities for the Disk Drive. The
Drive’s MPU is responsible for the following:

• Controlling data transfers, through its control

over the Common Data and Address Busses.

• Interpreting and controlling the accomplishment

of Console commands (temporarily stored in FLXM)
and Disk Drive operating instructions
(permanently stored in ROM).

• Controlling the Stepper, Disk Drive and Motor

Logics, which are buffered by the PIA.

2-4

The Drive’s ROM contains specific operating
instructions used by the MPU to accomplish a variety
functions.
These functions include telling the Disk controller
(WD1771-01) what task to perform.

The Drive’s RAM is used by the MPU for temporary
storage of both data and system information.

The Drive’s Data Output Buffer transfers the
formatted data through the PIA to the Data Out line
going to the Computer Console.

The Drive’s Power Up Logic circuit resets the MPU,
PIA and Data Interface Section whenever the Disk
Drive is turned on. The RESET references the
electrical circuits to their starting conditions.
Additionally, the Power Up Logic circuit locks the
Data Output Buffer off during a short period when the
Drive is turned on. This prevents random pulses
generated by the Drive’s circuitry (during the
initializing period) from being sent to the Console.

The Drive’s Clock circuitry generates both a crystal
controlled 1 MHz and a 500 kHz clock signal. The
1 MHz signal is used by the Data Interface Section.
The 500 kHz signal is used both as a clock signal to
the MPU, and to the data exiting from the Data
Input/Output and Manipulation Section into the Data
Interface Section.

2-5

DATA INTERFACE SECTION

Data Interface Section

The major element of the Data Interface Section is a
Floppy Disk Controller (FDC). The FDC is a highly
specialized microprocessor. It-is responsible for
the following activities:

• Combining data, timing and data validity pulses

into the serial format to be recorded.

• Separating the above and providing the output

data in parallel during a read operation.

• Controlling the Write and Erase Logic circuitry

during a write operation.

• Generating the data validity codes (called Cyclic

Redundancy Checks - or CRC’s) during a write
operation, and checking them during a read
operation.

2-6

The Drive’s Write and Erase Logic circuitry is
controlled by, and receives its data from the FDC.
Initially, the Data Gate converts the leading edge of
each pulse (data, clock, etc.) into a single
corresponding change of signed level. These levels
then determine the polarity of the Drive’s currents
applied to the Read/Write Head through the High and
Low level Drives, The Write Driver limits the write
currents.

The FDC combines clock
pulses with data to form
a serial signal.

The Data Gate converts
each pulse’s rising edge
into a logic level
change, as shown.

Basically, this is the signal applied to the head
during a write operation. The high levels out of the
Data Gate turn on the High level Driver, and the low
levels turn an the Low level Driver.
The Write and Erase Gate turns on both the Write and
Erase Drivers during a write operation, and turns
them off during a read operation. The Erase Driver
drives the Erase Head during a write operation. See
the Read/Write and Erase Head discussion for further
information.

Major elements of the Drive’s Read Data Conditioning
circuitry are:

• Differential Amplifier - Initial amplification of

Read/Write Head signals.

• Differentiator - Squaring up the two differential

amplifier outputs.

• Zero Crossing Detector - The single output

changes level whenever the two ,180° out-of-phase
input signals cross their zero axis
coincidentally (eliminates false pulses caused by

2-7

Read/Write Head signal decay, rather than
intentional signal level changes).

• Symmetry Amp - Ensures exact zero referencing of

the signal.

• Time Domain Filter - Trims and further shapes the

signal.

• Signal Gate - Produces a single pulse out for

each logic level transition at its input. This
results in the reproduction of the original FDC
signal.

During a read operation the Read/Write Head produces
two 180° out-of-phase signals. These are very weak,
highly distorted versions of the original signals
produced by the Write Logic Data Gate. The Read Data
Conditioning circuitry must amplify, square up and
filter the read signals to reproduce the original
serial string of bits produced by the FDC. This
reproduced signal is returned to the FDC by the Read
Data Conditioning circuitry (see figure below).

2-8

Two 180’ out-of-phase
signals are generated by
head during a read
operation and amplified by
the Differential
Amplifier.

The Differentiator squares
the two out-of-phase
signals.

The Zero Axis Crossing
Detector provides a single
output, further squared
and now without any signal
decay effects.

The Time Domain Filter
provides a signal with
very sharp leading and
trailing edges.

The Pulse Regenerator
converts each logic level
change into a single pulse,
recreating the original
signal produced by the FDC
during the write operation.

The Drive’s Write Protect circuit senses the presence
or absence of a special notch in one side of the
diskette casing. A write protected diskette’s notch
will be covered with an opaque tape. The circuit is
basically an LED/photo transistor sensor, whose
output is buffered before being applied to the FDC.
With an unprotected diskette, the sensor signal
allows the FDC to write data onto the diskette.

2-9

STEPPER MOTOR AND LOGIC

The Stepper Motor is a four phase motor with a 3.6°
rotor rotation per step. The motor has a total of 100
poles, providing 100 rotor steps for the motor’s full
360° rotation.

Stepper Motor and Logic

Each step change in the motor is translated
through a steel band connection to a single track
change far the Read/Write and Record Head assembly.
The diskette is divided into 40 tracks, so-the full
range of the Stepper Motor is not used.
The Stepper Logic is controlled from the PIA. The
four PIA signals are logic levels acting as the
Stepper Motor's four phase inputs. These levels, in
their various possible combinations, drive the
Stepper Motor to reposition the head assembly from
track to track.
The Stepper Motor is supplied with a nominal 3 to 10V
DC from the Power Supply.

2-10

DISKETTE DRIVE MOTOR AND LOGIC

The Diskette Drive Motor is a DC motor that
indirectly drives the diskette. The motor includes an
internal tachometer, whose output is monitored in the
Tach Feedback circuit. Variations in motor speed, as
sensed by the Tach Feedback circuit, vary the current
supplied to the motor. Diskette speed is set to 290
RPM ± l%.

Diskette Drive Motor and Logic

Motor rotation is translated into diskette rotation
via a pulley (attached to the motor shaft), a drive
belt and a flywheel attached to a diskette drive
spindle.
When a diskette has been inserted into the Disk Drive
and the front door has been latched closed, the
diskette is centered and clamped to the spindle by a
clutching cone assembly.
Whenever the Diskette Drive Motor is supplied with
power, the Drive’s BUSY lite (LED) is turned on.

2-11

DISK DRIVE SELECT

A double "Single pole - Double throw" switch gives
the Disk Drive operator the ability to assign a
number to, and therefore a code for addressing, each
of up to four Drives that could be daisy chained
together.
The switch is accessible at the rear of the Drive
chassis. The switch settings are read by the Drive’s
MPU through the PIA.

POWER SUPPLY

An external step-down transformer is supplied with
each Drive. The 120V AC line Power is dropped to 9
VAC by the transformer. This 9V AC enters to the
Drive through the "PWR" jack at the back of the
chassis.
Turning the Drive’s front panel "PWR" switch ON
applies the 9 VAC to a full wave bridge rectifier.
The Power Supply provides the following:

• The unregulated 9-10V DC Diskette Drive Motor

Supply.

• A regulated +5V DC.

• A regulated +12V DC (initially produced by a

voltage doubler circuit).

• A zener regulated -5 VDC (also produced by a

voltage doubler circuit).

2-12

A "PWR ON” lite (LED) is turned on through the -5 VDC
section of the supply.

READ/WRITE AND ERASE HEADS

A magnetic head converts electrical currents into
magnetic fields, and vice-versa. The Read/Write
Head consists primarily of two ferrite core halves,
wound with a centertapped coil. The centertap is
connected to the regulated +5V DC from the Power
Supply. One end of the coil is connected to the
High level Driver and the other end to the Low
level Driver.

WRITE OPERATION

Each logic level causes current to flow in one half
of the coil, with a high in one direction and a low
in the other. These currents set up corresponding
magnetic fields in the core halves, with a high
represented by a field in one direction, and a low by
a field in the opposite direction.

2-13

When the ferric oxide coating on the diskette is in

TRACK 13

TRACK 14

READ/WRITE

.036”

contact with the head, it completes the magnetic path
between the core halves. In response to the change
in direction of the magnetic field (logic level
change) passing through the diskette’s coating, the
oxide particles realign themselves. Particle
alignment in one direction represents a high level,
and alignment in the other direction a low level.

TRACK 15

ERASE HEAD GAPS

(STRADDLES TRACK)

GUARDBAND .008”

TRIM ERASED
TO .012”

GUARDBAND .008”

DISK ROTATION

HEAD GAP

.013”

During a write operation, the magnetic fields
coupling
through the diskette print a relatively wide (.013")
path of aligned particles. In order to prevent one
recorded track from interfering with either the next
inner or next outer track, a blank space, called a
guardband, is created between tracks. The Erase Head
creates these guardbands.
It straddles the Read/Write Head in such a way that
just after (.036") the data is written onto the
diskette, the Erase Head "tunnel" erases the track
width down to .012", leaving .008" quardbands between
tracks.

2-14

READ OPERATION

During a read operation, the very small fields
existing due to particle alignment on the diskette
couple through the head core halves. The diskette is
rotating, causing the specific field being felt in
the core halves to change for each change in particle
alignment (i.e. change of recorded logic level). The
changing fields in the core halves generate
corresponding currents in the head coil windings. It
is these very small signals that are applied to the
differential amplifier.

DISKETTE FORMATTING

The specific arrangement of information recorded onto
a diskette is called the diskette format. Unless a
Master Diskette is to be used, the diskette must be
initially formatted with a Disk Operating System
(DOS) software program.
The DOS software divides the diskette into 19 pie­shaped slices, 18 of which are called sectors. These
are not the same as the "709 FREE SECTORS" referred
to when you list the directory of a disk. Because the
diskette division is accomplished totally through
software, this process is called "soft sectoring".
The 18 sectors are equal in size, but the 19th (very
narrow) slice acts as an index to define the start of
each of the 40 tracks.

2-15

2-16

All 40 tracks receive the same formatting as follows:

*

256 bytes 00
1 byte FC (index mark)
11 bytes 00 or FF

6 bytes 00
1 byte FE
1 byte Track Number (00 thru 27 hex)
1 byte 00
1 byte Sector Number (01 thru 12 hex)
1 byte 00

**

1 byte CRC byte 2
1 byte CRC byte 1
17 bytes 00 (or 11 bytes FF and 6 bytes 00)
1 byte FB (data address mark)
128 bytes Data (FF for blank fill)
1 byte CRC byte 2
1 byte CRC byte 1
11 bytes 00 or FF

Cyclic Redundancy Checks (CRC's) are generated in the
Drive’s Floppy Disk Controller (FDC) during a write
operation. The FDC uses the recorded CRC's during a
read operation to verify the data. CRC’s are similar
in function to the checksums used between the
Computer Console and the Disk Drive’s MPU.

* Appear only once per track for indexing.
** Repeated 18 times per track, producing the
full 18 sectors.

2-17

BLOCK DIAGRAMS

AND

SCHEMATICS

On the following pages are block diagrams and
schematics for the Disk Drive. Further understanding
of the system’s operation can be obtained by
comparing these.

3-1

ATARI 810 DISK DRIVE BLOCK DIAGRAM

3-2

ATARI 810 SIDE BOARD BLOCK DIAGRAM

3-3

ATARI 810 SIDE BOARD SCHEMATIC DIAGRAM

3-4

ATARI 810 REAR BOARD BLOCK DIAGRAM

3-5

ATARI 810 REAR BOARD SCHEMATIC DIAGRAM

3-6

FLOPPY QUICKCHECK

4-1

This procedure should he completed both as a pre-

WRITE

service checkout and a final (post-service) checkout
for the Disk Drive.
As a pre-service checkout, it will assist in
identifying problems in the Drive.
As a final checkout, it will ensure that all repairs
and alignments were successfully completed.
This procedure follows this flow chart:

SETUP

PASS

BOOTING

TEST

PASS

FAIL

TROUBLESHOOTING

PROCEDURE

PROTECT

TEST

PASS

FORMATTING

TEST

PASS

BOOTING

TEST

PASS

BOOTING

TEST

UNIT

GOOD

FAIL

FAIL

FAIL

FAIL

All tests must be completed in the sequence shown.

4-2

The following are required to perform these
procedures:

A. Atari 400/800 Computer Console with a BASIC

cartridge and minimum 16K RAM installed.

B. I/O cables and Console/Drive power packs.
C. TV.
D. Master Disk File Manager diskette with

writeprotect notch taped.

E. Blank scratch diskette (not write-protected).
F. Prerecorded sample diskette with DOS and sample

programs recorded on a known "good" Disk Drive.
I
SETUP

1. Connect the Drive to the Console and connect both
to power.

2. Turn the Drive ON and wait for the BUSY lite to go
off. If BUSY lite does not come on and then go off,
recheck connections then refer to the Troubleshooting
Guide.

BOOTING TEST

1. Insert A Master Disk File Manager diskette into

the Drive and close the Drive’s door.

2. Turn the Console OFF, then ON. Verify that data

is transferred from the diskette to the Console
RAM (turn up the TV sound and listen for the
"buzz. ..buzz...buzz...etc” , this should take
about 10 seconds). When completed, the TV screen
should display the word READY.

3. If the TV displays any ERRORS or does not show

READY very shortly, repeat step 2. If the system
still will not "BOOT UP", recheck your
Console/Drive system and hookup for
misconnections or gross equipment failures. If
none are found and the system continues to
ERROR, refer to the Troubleshooting Guide in
this manual.

4. When the system has booted:

a. type DOS (Disk Operating System)
b. press the RETURN key

4-3

5. Verify that the DOS menu appears on the TV

screen. Refer to the Troubleshooting Guide if
you encounter an ERROR on the TV screen.

WRITE PROTECT TEST

This test must be completed with the write-protected
Master diskette installed. The TV screen should be
displaying the DOS menu from the Booting Test.

1. At the Console:

a. type I (capital letter)
b. press RETURN
c. type 1 (number one)
d. press RETURN
e. type y
f. press RETURN t

2. Verify that, the TV screen displays ERROR-144.

If it does, the write protect circuit is
operating correctly, go on to step 3. If it does
not:
a. Repeat Step 1 again.
b. If the ERROR-144 still does not appear, refer

to the Troubleshooting Guide.

3. Remove the Master diskette from the Drive.

FORMATTING TEST

CAUTION: The formatting operation erases the contents
of a diskette.
This test must be completed with the DOS from the
Master diskette still stored in the Console RAM.

1. Insert a non-write-protected scratch diskette

into the Drive and close the door.

2. At the Console:

a. press SYSTEM RESET
b. type DOS
c. press RETURN
d. type I (capital letter)
e. press RETURN
f. type 1 (number one)
g. press RETURN
h. type Y
i. press RETURN

4-4

3. Verify that after about 45 seconds OE formatting

the Drive’s BUSY lite turns OFF and no ERRORS
have been displayed on the TV screen (refer to
the Troubleshooting Guide for any ERRORS).

4. At the Console:

a. type A
b. press RETURN
c. press RETURN
d. Verify that "709" or "FREE SECTORS 709" is

displayed at bottom of screen. If not, refer
to the Troubleshooting Guide.

5. Press RETURN to get back to "MENU"

WRITE VERIFICATION

This test must immediately follow the FORMATTING
TEST.

1. At the Console:

a. type I
b. press RETURN
c. type Y
d. press RETURN

2. Verify that the TV screen displays SELECT ITEM

after a short period of time. If it does not,
refer to the Troubleshooting Guide.

3. At the Console:

a. type A
b. press RETURN
c. press RETURN

4. Verify that the TV screen displays DOS.SYS and

number of sectors used, followed by the number
of sectors remaining. If it does not reseat the
procedure. If the second attempt fails, refer to
the Troubleshooting Guide.

4-5

5. Delete the file as follows:

a. At the Console:

1. press RETURN

2. type D

3. press RETURN

4. type DOS.SYS

5. press RETURN

6. type y

7. press RETURN

b. After a "SELECT ITEM” appears, at the

Console:

1. type A

2. press RETURN

3. press RETURN

c. Verify that the TV screen indicates that

there are 709 free sectors remaining.

6. Remove the blank scratch diskette from the Drive.

4-6

COMPATIBILITY TEST

This test verifies that the Drive can read programs
from a diskette recorded on a known "good" Drive.

1. Insert a sample diskette into the Drive.

2. Turn the Console OFF, then ON.

3. Verify that after about 10 seconds, the TV

screen displays READY.

4. At the Console:

a. type DOS
b. press RETURN

5. Verify that the DOS menu appears on the TV

screen, indicating that the diskette data was
correctly loaded into the Console RAM. Refer to
the Troubleshooting Guide in case of any ERRORS.

6. At the Console:

a. type A
b. press RETURN
c. press RETURN

7. Verify that the Drive’s BUSY lite comes ON as

the Drive loads its directory listing into the
Console. The directory should appear on the TV
screen.

8. Choose a program you wish to load.

At the Console:
a. press RETURN
b. type B
c. press RETURN
d. type LOAD "D:NAME OF PROGRAM"
e. press RETURN

9. Verify that the Drive’s BUSY lite comes on as

the Drive loads the selected program. After
several seconds, the word READY should appear at
the top of the screen. If not, refer to the
Troubleshooting Guide.

10. At the Console:

a. type RUN

b. press RETURN
Verify that the selected program runs correctly.
If it ERRORS, refer to the Troubleshooting Guide.

4-7

5-1

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION

1

Drive will not turn
ON.

Drive will not turn

2

OFF.

Diskette does not

3

turn.

4

Diskette speed slow
or varying.

Diskette won’t
eject when front

5

door is opened.

Front door won’t

6

open

7

Drive/Console
System not boot-up

A. Defective transformer.
B. Electrical malfunction:

Power Switch on Side
PCB, Power Supply on
Rear PCB.

A. Defective Side and/or

Rear PCB

A. Drive Belt has fallen
off Flywheel/Pullen or is
broken.

B. Drive Motor defective.
C. Clutch Cone not

clamping diskette.

D. Electrical malfunction
Drive Motor Circuit. Rear
PCB.

A. Drive Motor Tach line
out of place.

B. Write Protect Circuit
bad.

C. Drive Belt incorrectly
tensioned.

D. Drive Belt stretched.
E. Electrical malfunction

Drive Motor circuit Rear
PCB.

F. Spindle Bearing
freezing.

A. Eject mechanism need
adjusting or is broken.

B. Clutch Cone-to-Spindle
clearance (door open0too
small.

A. Door latching mechanism
need adjustment or is
broken.

A. Drive Motor speed
incorrect.

B. Can’t find Track 00.

C. Electrical malfunction
Side or Rear PCB(s).

D. Stepper Motor
malfunctioning.

E. Radial track
misalignment.

F. Bad Head

5-2

A. Replace
transformer.

B. Replace and/or
troubleshoot PCB(s).

A. Replace or repair
PCBs.

A. Reposition or
replace Drive Belt.

B. Replace Drive
Motor.

C. Adjust or replace
Clutch Cone assembly.

D. Replace and/or
troubleshoot PCB.

A. Connect green Motor
Harness to center
terminal of Write
Protect Harness.

B. Replace transport
left Side Plate.

C. Adjust Belt tension
D. Replace Drive Belt.
E. Replace and/or

troubleshoot PCB.
F. Replace Spindle

Bearing.

A. Adjust or replace
Eject Mechanism.

B. Shim the Clutch
Cone assembly.

A. Adjust or replace
door latch.

A. Adjust Drive Motor
speed.

B. Adjust Track 00
stop setscrew.

C. Replace and/or
troubleshoot PCB(s).

D. Replace Stepper
Motor.

E. Complete radial
track alignment.

F. Replace Head
assembly.

Continue…

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION

8

Occasional read
errors all tracks.

Occasional read
errors inner

9

tracks.

Occasional read

10

errors outer
tracks.

Drive

11

incompatibility

Various errors code

12

during operation.

Drive writes onto

13

write-protected
diskettes.

A. Damaged diskette.

B. Dirty or magnetized
head.

C. Worn or dirty head
pressure pad.

D. Overstressed pressure
pad arm spring.

A. Drive Motor speed

incorrect.

B. Electrical malfunction

in read circuit.

A. Drive Motor speed

incorrect.

B. Electrical malfunction
in read circuit.

A. Drive Motor speed
incorrect.

B. Radial track
misalignment.

A. Eject mechanism need
adjusting or is broken.

B. Clutch Cone-to-Spindle
clearance (door open0too
small.

A. Malfunctioning Write­Protect circuit.

A. Replace diskette.

B. Clean and
demagnetize head.

C. Replace head
pressure pad.

D. Replace spring or
head assembly.

A. Adjust Drive Motor
speed.

B. Replace and/or
troubleshoot Rear PCB,
Side PCB or Head.
(Check for slow Q102
or Z104 on Side PCB.

A. Check to ensure
diskette is not write­protected.

B. Replace Z105.
C. Replace and/or

troubleshoot PCB(s),
transport.

A. Adjust Drive Motor
Speed.

B. Replace and/or
troubleshoot Rear PCB,
Side PCB or Head.

A. Adjust or replace
Eject Mechanism.

B. Complete radial
track alignment.

A. Check write-protect
LED/photo-transistor,
wiring harness
connections. Transport
left sideplate.

5-3

DISSASSEMBLY / REASSEMBLY

6-1

DISASSEMBLY AND REASSEMBLY

The level of Disk Drive disassembly will vary with
the specific problem encountered. Some procedures
list steps which are themselves procedures: i.e.
"Disassemble the Drive case." When you encounter an
underlined step, turn to that procedure first and
follow it before proceeding.

SPECIAL NOTES

1. Refer to the Disk Drive and 400/800 Operators

Manuals for proper Drive setup and operation.

2. Disk Drive circuitry includes static sensitive

MOS devices. All Drive repairs should be
performed at static protected work surfaces.
Anyone handling Drive PCBs should wear a
grounding strap.

3. To prevent thread damage, use only the specified

screws.

4. Overtightening screws will strip the threads on

plastic and aluminum parts. Do not exceed 6 inch
pounds torque for plastic parts, or 10 inch
pounds torque for aluminum parts.

6-2

5. Internal wiring connections are made with wiring

DRIVE

COMMON

harnesses terminated by nonpolarized pins and
jacks. Be sure all pins and jacks are correctly
installed before trying to operate the Disk
Drive.

6. When reassembling the Drive, ensure that all

wiring harnesses are routed in such a way as to
prevent them from being pinched between
reassembled parts.

DISASSEMBLY FLOW CHART

CASE

BASEPLATE

STEPPER

MOTOR

HEAD

ASSEMBLY

TRANSPORT

DRIVE

BELT

CARRIER

ASSEMBLY

FLYWHEEL

BEARINGS

RF SHIELD
(SIDE PCB)

DRIVE

MOTOR

SIDE PCB

REAR PCB

Q113/A108

Identify the level of required and complete
disassembly the sequence of steps indicated above.

6-3

DISSASSEMBLY

I
DISASSEMBLING THE DISK DRIVE CASE

WARNING: Unplug the Drive’s AC transformer from AC
power BEFORE opening the case.

1. With the Disk Drive rightside up on a suitable

work surface, locate and remove the four adhesive
screw hole covers on the tophousing.

2. Locate and remove the four screws securing the

tophousing to the base.

3. Lift the tophousing from the base, and set it

aside.

CAUTION: The record/playback and erase head sub­assembly is extremely sensitive to magnetic fields.
DO NOT use magnetized tools or articles when working
inside the Drive case or near the Drive transport.

6-4

REMOVING THE COMMON BASEPLATE

NOTE : Removal of either the side PCB, rear PCB
or Drive transport requires removal of their
common baseplate from the Disk Drive base.

1. Disassemble the Disk Drive case.

2. Disconnect the AC transformer power cord from the

PWR jack at the rear of the Drive chassis.

3. Disconnect any I/O cables from the I/O CONNECTORS

at the rear of the Drive chassis.

4. Locate and remove the five screws securing the

common baseplate to the base.

5. Carefully lift the baseplate from the base. Note

that each of the bosses in the base is topped
with a rubber washer.

6-5

NOTE: As you lift the baseplate from the base, the
front coverplate will lift out at the same time.
Remove the coverplate from the baseplate and set it
aside.

6. Place the baseplate on a suitable static

protected work surface.

REMOVING THE SIDE PCB

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Locate and disconnect the write protect wiring

harness (nonpolarized - black, green, (blank),
red, black) from the side PCB.

4. Locate and disconnect the stepper motor wiring

harness (nonpolarized - black, white, red, green,
brown) from the side PCB.
NOTE: See Appendix for alternate wiring harness
arrangement.

6-6

5. Locate and remove the three screws securing the

side PCB and its center ground bracket to the
common baseplate.

6. Grasp the side PCB at both its front edge and its

upper rear corner. Lift the PCB straight up to
disengage its rear jack from the row of pins
NOTE: You may have to rock the PCB slightly to
overcome the jack-to-pin tension between the two
PCBs.

7. Place the side PCB on a static protected work

surface.

6-7

REMOVING THE RF SHIELD (SIDE PCB)

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the side PCS from the common baseplate.

4. Locate and carefully straighten the three tabs

securing the RF shield case halves together on
the side P6B.
CAUTION: Excessive bending of the metal tabs will

break them. DO NOT bend the tabs anymore
than necessary.

5. Locate and remove the two screws securing the

case halve to the ground bracket and PCB.

6. Carefully disengage the case halves from each

other and the PCB. Set the case halves aside.

6-8

REMOVING THE DRIVE TRANSPORT

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the side PCB.

4. Grass the transport securely, tip the assembly

upside down, and place it on a suitable work
surface.

5. Locate and remove the four screws that secure the

transport to the baseplate. The screws are
accessible only from the underside of the
baseplate.

CAUTION: The transport provides critical
mechanical alignments necessary for proper Disk
Drive operation. Be very careful not to jar or
damage the transport or any of its associated
sub-assemblies and components.

6. Place the transport and baseplate on a suitable

work surface.

6-9

REMOVING THE REAR PCB

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the side PC8 from the common baseplate.

4. Locate and remove the four screws securing the

rear PCB to the common baseplate.

5. Grasp the rear PCB on both side edges. Carefully

lift the board straight up far enough to
disengage the board’s two right side jacks from
the six device pins.

NOTE: You may have to rock the PCB slightly to
overcome the jack-to-pin tension between the PCB
and the pins attached to the common baseplate.

6. Lift the rear PCB away from the baseplate and

place it on a suitable work surface.

6-10

REMOVING Q113 (TRANSISTOR)/A108 (VOLTAGE REGULATOR)

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the side PCB from the common baseplate.

4. Remove the rear PCB from the common baseplate.

5. Locate and remove the single screw securing the

device (either transistor Q113 or voltage
regulatorAl08) to the common baseplate.

NOTE: If you are removing Q113 you should find an
insulating plate between the back of the device
and the common baseplate. Also, both Q113 and
A108 use the common baseplate as a heatsink. Each
device and Q113’s insulating plate should be
coated with heat transfer compound.

6. Lift the device (Q113 or A108) from the baseplate

and set aside.

6-11

REMOVING THE TRANSPORT DRIVE BELT

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the common

baseplate.

4. Carefully lay the transport on its side.

5. Locate and remove the drive belt.

NOTE: TO remove the drive belt without stretching or
damaging rotate the large flywheel (naked for strobe)
while easing the belt off the outside edge of the
flywheel.

6-12

REMOVING THE TRANSPORT DRIVE MOTOR

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the common

baseplate

4. Remove the drive belt from the transport.

5. Locate and disconnect the single black ground

lead coming from the drive motor wiring harness
and going to the transport casting.

6. While supporting the drive motor with one hand,

locate and remove the two screws securing the
drive motor to the transport casting.

7. Separate the drive motor from the casting.

6-13

REMOVING THE CARRIER ASSEMBLY

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the common

baseplate.

4. Locate the head assembly and slide the assembly

all the way to the rear of its travel.

5. Locate and loosen approximately two full turns,

but do not remove, the two screws securing the
carrier assembly to the rear of the transport
casting.

6. Locate the four screws securing the front panel

bezel to the side guide assemblies and the
transport casting.

7. Loosen (do not remove) the two bottom screws

approximately four full turns.

8. Remove the two top screws.

6-14

9. Push the door release button at the front of the

transport to disengage the carrier assembly from
the door latch. Lift the assembly far enough to
clear the latch mechanism and release the button.
Lower the door to a resting position.

10. Now completely remove the two screws at the rear

of the transport casting.

11. Pull the top of the front panel bezel forward.

12. Carefully, lift the carrier assembly out of the

transport.

CAUTION: You will have to tilt the carrier assembly
slightly to clear the head assembly’s pressure pad
arm. DO NOT lift the pressure pad arm higher than it
would be lifted by the door arm during normal Drive
operation. Lifting the pad arm too far will distort
its pressure spring changing the pressure pad’s
loading effect on the head.

6-15

REMOVING THE TRANSPORT FLYWHEEL/DRIVE SPINDLE

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the comma

baseplate.

4. Remove the drive belt from the transport. .

5. Remove the carrier assembly from the transport.

6. Carefully lay the transport on its side.

7. Locate the single screw in the center of the

flywheel. Holding the flywheel with one hand,
remove the screw.
NOTE: See the following illustration of the
flywheel/casting/spindle relationship. The
specific number and placement of the washers is
very important and helps to determine diskette
speed during operation. DO NOT lose any of the
washers you remove during this step.

6-16

8. Being very careful not to lose any washers, hold

the drive spindle with one hand and carefully
pull the flywheel away from the casting with the
other hand.

9. Pull the spindle from the casting.

6-17

REMOVING THE TRANSPORT SPINDLE SHAFT BEARINGS

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the common

baseplate.

4. Remove the Drive belt from the transport.

5. Remove the carrier assembly from the transport.

6. Remove the flywheel and drive spindle from the

transport.

7. The top spindle shaft bearing may have lifted

from the casting when you removed the drive
spindle. If it did not, very carefully pry the
bearing out of the casting.

8. Very carefully push the bottom bearing out of the

casting (push from the top side of the casting,
being very careful not to damage the casting
bore).

6-18

REMOVING THE HEAD ASSEMBLY

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive base.

3. Remove the Drive transport from the common

baseplate.

4. Remove the Drive belt from the transport.

5. Locate the nylon clamp securing the

record/playback and erase head I/O wiring harness
to the right rear corner of the casting. Release
the clamp from the casting.

6. Push the head assembly as far to the rear of the

Drive as it will slide.

7. Locate and remove the ground lead (black wire

from the drive motor wiring harness) faston from
the rear of the casting.

6-19

8. Locate the two screws securing the stepper motor

positioning band to the right side of the head
assembly.
a. Remove the rear screw, being very careful not

to crimp or damage the band, and noting the
screw and washer arrangement.

b. Slide the head assembly carriage forward

enough to allow you to remove the front band
screw. Remove the front screw, again noting
the screw and washer arrangement.

NOTE: The stepper motor positioning band is very
delicate and very important to the operation of the
Drive. DO NOT kink or damage the band in any way.

9. Locate the two screws securing the carriage

guiderod clamps to the drive casting.

10. Remove the two screws and lift the guiderod

clamps away from the assembly.

6-20

11. Carefully pry the two guiderods up out of their

locating notches in the drive casting.

12. Gently lift the head assembly carriage and

guiderods away from the casting. You will have to
feed the head I/O cable through the casting at
the same time.
CAUTION: The head is subject to external magnetic
fields. DO NOT use magnetized tools or allow the
head to get near any equipment producing strong
magnetic fields.

13. Slide the guiderods out of the carriage.

6-21

REMOVING THE STEPPER MOTOR

1. Disassemble the Disk Drive case.

2. Remove the common baseplate from the Drive case.

3. Remove the Drive transport from the common

baseplate.

4. Locate the two screws securing the stepper motor

positioning band to the right side of the head
assembly.

a. Remove the rear screw, being very careful not

to crimp or damage the band, and noting the
screw and washer arrangement.

b. Slide the head assembly carriage forward

enough to allow you to remove the front band
screw. Remove the front screw, again noting
the screw and washer arrangement.

NOTE: The stepper motor positioning band is very
delicate and very important to the operation of the
Drive. DO NOT kink or damage the band in any way.

6-22

5. Locate the allen-head setscrew securing the head

positioning strap pulley to the stepper motor
drive shaft (topside of casting).

6. Back the setscrew out about 1turn

(counterclockwise).

7. Remove the band/pulley from the stepper motor

shaft and set it aside.

8. Locate the two nuts securing the stepper motor

to the casting.

9. Lay the casting on its left side.

10. While supporting the stepper motor with your

right hand, remove the two securing nuts.

11. Carefully separate the motor from the chassis,

while pulling the motor wiring harness out of
its chassis slot.

6-23

REASSEMBLY

DRIVE

H

EAD

TRACK

ALIGN

STEPPER

MOTOR

HEAD

ASSEMBLY

BEARINGS

FLYWHEEL

CARRIER

ASSEMBLY

DRIVE

BELT

BELT

ADJ.

DRIVE

MOTOR

Q113/A108

REAR

BOARD

RF SHIELD
(SIDE PCB)

TRANSPORT

HEAD

SPEED
CNTRL

CLEAN

TRACK
00 STOP

COMMON

BASEPLATE

DRIVE

CASE

SIDE PCB

FINAL

CHECK

Locate the beginning point of your reassembly, and
follow the instructions called out in this flow chart
in the order shown.

6-24

INSTALLING THE STEPPER MOTOR

1. Install a split rubber grommet on the stepper

motor wiring harness.

2. Lay the transport on its left side.

3. Position the stepper motor to the underside of

the transport casting. The motor’s wiring harness
should lie toward the rear center of the casting.

CAUTION: The head is subject to magnetization from
external fields. DO NOT use magnetized tools or allow
the head to get near any equipment producing strong
magnetic fields.

6-25

4. Install a flatwasher, a splitring lockwasher, and

a l/4" hexnut onto each of the two stepper motor
stud bolts projecting through the top of the
casting. Lightly tighten the nuts.

5. Carefully install the head positioning band

pulley onto the stepper motor drive shaft
(projecting through the top of the casting). If
the pulley does not easily slip onto the motor
shaft, back the pulley’s allen-head setscrew a
little farther out of the pulley. DO NOT tighten
the setscrew at this time.

NOTE: The stepper motor positioning band is delicate
and VERY important to the operation of the Drive. DO
NOT kink or damage the band in any way.

6-26

6. Carefully position the head assembly, so that you

can connect the positioning band to the
assembly’s right rear corner.

7. Install, but do not tighten, the rear screw,

splitring lockwasher, and special bracket washer
to hold the rear section of the positioning band
to the head assembly.

8. Carefully pull the front section of the

positioning hand forward until its screw hole is
located over the matching screw hole on the front
corner of the head assembly.

9. Install, but do not tighten, the screw, splitring

lockwasher, and flatwasher to secure the band to
the head assembly.

10. Gently slide the head assembly back and forth on

its guiderods. This will center the band pulley
on the stepper motor shaft.

11. Tighten the rear band retaining screw.

CAUTION: DO NOT exceed 6 inch lbs. torque when
tightening screws into plastic parts.

6-27

12. Use a pointed tool (i.e. X-acto knife point etc.)

to hook the small hole on the front end of the
positioning band. Pull forward slightly on the
band while tightening the front band retaining
screw.

13. Slide the wiring harness, grommet up into the

slot at the rear of the transport casting.

14. Attach the transport to the common baseplate.

15. Attach the common baseplate to the Drive base.

INSTALLING THE HEAD ASSEMBLY

CAUTIONS: The head is subject to magnetization from
external fields. DO NOT use magnetized tools or allow
the head to get near any equipment producing strong
magnetic fields. The head is also damaged by dirt and
oils.
DO NOT touch either the head or the pressure pad with
your fingers.
DO NOT lift the pressure pad arm farther from the
head carriage than the arm would be lifted during
normal Disk Drive operations. Lifting the arm too far
will distort its pressure spring, changing the arm’s
loading effect on the head during operation.
The stepper motor positioning band is delicate and
very important to the operation of the Drive. DO NOT
kink or damage the band in any way.

6-28

1. Slide the two guiderods into the sides of the

head assembly carriage.

2. Carefully lower the carriage/guiderods assembly

into position in the transport casting. Ensure
that the head wiring harness lies down in the
underside of the transport.

3. Wrap a small piece of masking tape

around the head assembly’s wiring
harness, about 3" from the head.
Install the nylon cable clamp over
the tape and snap the clamp into
the hole provided at the back of
the casting.

4. Feed the wiring harness up through the

rectangular hole at the right rear corner of the
transport casting.

5. Center (front-to-back) the two head assembly

guiderods in their transport casting slots.

6-29

6. Position the two guiderod clamps onto the

casting, over the ends of the guiderods.

7. Install, but do not tighten, the front clamp

screw including a splitring lockwasher.

8. Install, but do not tighten, the rear clamp screw

including two male faston terminals and a
splitring lockwasher.

9. Tighten the two clamp screws to 10 inch lbs.

torque

6-30

10. Carefully position the head assembly so that you

can connect the positioning band to the assembly
right rear corner.

11. Install, but do not tighten, the rear screw,

splitring lockwasher, and special bracket washer
to hold the rear section of the positioning band
to the head assembly.

12. Carefully pull the front section of the

positioning band forward until its screw hole is
located over the matching screw hole on the front
corner of the head assembly.

13. Install, but do not tighten, the screw, splitring

lockwasher, and flatwasher to secure the band to
the head assembly.

14. Locate the allen-head setscrew securing the

positioning band pulley to the stepper motor
driveshaft. Back the setscrew out
(counterclockwise) about l/4 turn.

15. Gently slide the head assembly back and forth on

its guiderods. This will center the band pulley
on the stepper motor shaft.

16. Tighten the rear band retaining screw.

CAUTION: 00 NE exceed 6 inch lbs. torque when
tightening screws into plastic parts.

6-31

17. Use a pointed tool (i.e. X-acto knife point,

etc.) to hook the small hole on the front end of
the positioning band. Pull forward slightly on
the band while tightening the front band
retaining screw.

18. Attach the black ground lead (drive motor wiring

harness) to one of the faston lugs at the rear of
the transport.

19. Attach the carrier assembly to the transport.

6-32

INSTALLING THE TRANSPORT SPINDLE SHAFT BEARINGS

1. Gently insert either the top or bottom (or both)

shoulder bearings into the casting bore. There
should be a slight friction fit.

NOTE: If excessive force is required, you probably
have incorrectly identified the bearing. Obtain the
correct bearing before proceeding.

2. Ensure that the shoulder of the bearing is firmly

seated flat against the casting.

3. Attach the flywheel and drive spindle to the

transport.

6-33

INSTALLING THE TRANSPORT FLYWHEEL / DRIVE SPINDLE

1. Lay the transport casting on its side.

2. From the top side of the casting, insert the

diskette drive spindle into the shoulder
bearings.

3. Assemble the necessary combination of washers

along with the flywheel and screw. See the
illustration for the flywheel/casting/spindle
relationship. The specific number and placement
of the washers is very important and helps to
determine diskette speed during operation.

6-34

4. From the bottom side of the casting, position the

flywheel, screw and washer combination over the
bottom of the spindle shaft. Screw the assembly
together. Torque the screw to 6 inch lbs.

5. Rotate the flywheel and check for wobble, runout

or binding of either the flywheel or drive
spindle. Adjust the assembly as necessary.

6. Attach the carrier assembly to the transport.

6-35

INSTALLING THE CARRIER ASSEMBLY

CAUTIONS: This procedure requires that you lift the
head assembly pressure pad arm in order to position
its lift arm onto the carrier assembly. DO NOT lift
the pressure pad higher than it would be lifted by
the carrier assembly during normal operations.
Lifting the pad arm too far will distort its pressure
spring, changing the pad’s loading effect on the
head. The head is subject to magnetization from
external fields. DO NOT use magnetized tools or allow
the head to get near any equipment producing strong
magnetic fields.

1. Ensure that the transport front panel bezel is

tilted forward from both guide assemblies for
extra clearance at the top.

6-36

2. Carefully lower the carrier assembly into

position over the transport casting. Lift the
head assembly’s pressure pad arm just enough to
position it onto its carrier assembly slide area.

3. Install and slightly tighten the two screws,

splitring lockwashers, and flatwashers at the
rear corners of the carrier assembly.

4. Push the bezel back to its normal position and

install the two top screws.

6-37

5. Tighten the four screws securing the bezel to the

transport.

6. Latch the carrier assembly closed (down) at the

bezel.

7. Horizontally center the door in the door opening

of the bezel.

6-38

8. Tighten (10 inch lbs.) the two screws securing

the rear corners of the carrier assembly to the
rear of the transport casting.

9. Press the front door release button. Ensure that

the door opens and the carrier assembly lifts the
head assembly pressure pad arm.

10. With the door open, observe the gap between the

top edge of the diskette drive spindle and the
bottom edge of the clutch cone assembly. Be sure
a diskette can move in and out without being
scratched or pinched.

NOTE: The spindle/cone clearance is critical to
ensure that the diskette is ejected when opening the
front door. Too little clearance may cause the back
edge of the cone to catch the edge of the diskette
hub hole, preventing the diskette from being
ejected. Test the ejection process using a standard
diskette.

11. To adjust the clearance, compress the clutch cone

into the door arm, forcing the clutch cone shaft
up out of the top of the carrier assembly.

12. Locate and remove the retaining clip from the

shaft.

13. Place another flatwasher over the shaft and

replace the retaining clip.

14. Release the clutch cone and return to step 10.

6-39

15. With the carrier assembly open, push the diskette

eject block (right rear corner) until it latches
into its rear position under the latch lever.

16. Close the carrier assembly and then press the

release button to reopen the door.

17. Cheek to see that the diskette eject block freely

returned to its forward position when the carrier
assembly opened.

18. If the block did not return, bend either the

latching lever or the lever lifting arm to adjust
the mechanism.

19. Repeat steps 15 thru 18 until the diskette eject

mechanism works as indicated.

20. If necessary, install the drive belt.

21. Attach the transport to the common baseplate.

6-40

INSTALLING THE DRIVE MOTOR

1. Lay the Drive transport on its side.

2. Position the drive motor onto the top side of the

casting. The motor’s wiring harness should exit
the motor toward the center rear of the
transport.

3. While supporting the motor with one hand, install

the two screws, splitring lockwashers, and
flatwashers to secure the motor to the transport.

4. Torque the two screws to 10 inch lbs.

5. Attach the drive belt to the transport.

6-41

INSTALLING THE TRANSPORT DRIVE BELT

1. Lay the transport on its side.

2. Loop the drive belt over the drive motor drive

hub. Carefully ease the belt onto the flywheel
while rotating the flywheel.

NOTE: DO NOT stretch or damage the drive belt. It is
primarily responsible for diskette speed and any
variations in diskette speed caused by a stretched or
damaged drive belt can cause errors during read and
write operations.

3. Refer to the adjustments section of this manual

and complete the drive belt adjustment.

4. Attach the transport to the common baseplate.

6-42

INSTALLING Q113 (TRANSISTOR)/A108 (VOLTAGE REGULATOR)

1. Bend the leads of the device you are about to

install as shown above.

2. If you are installing Q113(transistor):

a. Apply heat transfer compound to both sides of

the mica insulating plate.

b. Place the insulating plate into location on

the common baseplate.

c. Place the transistor into position on top of

the insulating plate.

d. Secure the transistor/insulating plate

combination to the common baseplate with a #4­40 x 3/8" PHIL HD. SCREW, shoulder washer, #4
splitring lockwasher, and a #4 ST2 hexnut.

6-43

3. If you are installing A108(voltage regulator):

a. Apply heat transfer compound to the back of

the voltage reql1ator. :

b. Position the regulator onto the common

baseplate.

c. Secure the device to the baseplate with

a #4 x l/4 THD F PHIL HD. screw.

4. Attach the rear PCB to the common baseplate.

6-44

INSTALLING THE REAR PCB

1. Carefully lower the rear PCB into position on the

common baseplate. Ensure that the six device legs
at the right side of the baseplate are correctly
seated into the two three-pin sockets on the PCB.

2. Install and tighten the four screws(#6-32 x l/4"

PHIL HD.) and lockwashers(#6 splitring) to secure
the PCB to the baseplate.

3. Connect the transport to the common baseplate.

6-45

INSTALLING THE DRIVE TRANSPORT

CAUTION: The transport provides critical mechanical
alignments necessary for proper Disk Drive operation.
Be very careful not to jar or damage the transport or
any of its associated subassemblies and components.

1. Carefully set the transport upside down on a

suitable work surface.

2. Gently set the transport (upside down) on top of

the transport.

3. Install and tighten the four screws(t6-32 x l/4"

PHIL HD.) and lockwashers (#6 splitring) to
secure the transport to the baseplate.

4. Set the assembly rightside up on the work

surface.

6-46

5. Locate and connect the record/playback and erase

head I/O wiring harness (shielded red, (blank),
blue and either white, black or black, white) to
the rear PCB (nonpolarized, X4).

6. Locate and connect the drive motor/ground wiring

harness (yellow, green, blue, red, black) to the
rear PCB (nonpolarized, #3).

7. If you removed the side PCB, follow the

procedures to attach the PCB to the common
baseplate.

8. If you did not remove the side PCB during

disassembly:
a. Locate and connect the stepper motor wiring

harness (black, white, red, green, brown) to
the side PCB (nonpolarized, #2).

b. Locate and connect the write protect wiring

harness (black, green, (blank), red, black) to
the side PCB (nonpolarized, #l).

9. Go on to step 10.

10. Attach the common baseplate to the Drive base.

NOTE: See Appendix for alternate wiring harness
arrangement.

6-47

INSTALLING THE RF SHIELD (SIDE PCB)

CAUTION: Excessive handling of the locating tabs on
the shield case will break them. DO NOT bend the tabs
anymore than absolutely necessary.

1. Carefully position the case halves on the side

PCB.

2. Position the ground bracket onto the side PCB.

3. Install and tighten the two screws 186-32 x 5/16"

TRD F, PHIL HD.) to secure the ground bracket to
the PCB and case halves.

4. Locate and bend the three tabs securing the RF

shield case halves together.

5. Connect the side PCB to the common baseplate.

6-48

INSTALLING THE SIDE PCB

1. Position the side PCB on the common baseplate

(with rear PCB installed).

2. Gently seat the multipin socket at the rear lower

edge of the side PCB down onto the pins
protruding from the rear PCB.

3. Install and tighten the three screws (116-32 x

5/16" THD F, PHIL HD.) that secure the side PCB
and its ground bracket to the common baseplate.

6-49

4. Locate and connect the stepper motor wiring

harness (black, white, red, green, brown) from
the Drive transport to the side PCB
(nonpolarized, ’P2).

5. Locate and connect the write protect wiring

harness (black, green, (blank), red, black) to
the side PCB (nonpolarized, #1).

6. Attach the common baseplate to the Drive base.

NOTE: You may also have this wiring harness
arrangement.

6-50

INSTALLING THE COMMON BASEPLATE

1. Ensure that every boss in the base (even those

not used to secure the baseplate is topped with a
rubber isolation washer.

2. Position the front coverplate onto the

baseplate/transport/PCB assembly.

3. Carefully lower the baseplate into position in

the Drive base, ensuring that the cover-plate is
also correctly positioned in the base.

4. Install and tighten the five screws (6 - l/2" BT.

PHIL HD.) securing the common baseplate to the
drive base.

6-51

5. Refer to the adjustments section of this manual

and complete the head cleaning and
demagnetization procedure.

6. Refer to the adjustments section of this manual

and complete the radial track alignment, speed
control adjustment, and track 00 end stop
adjustment.

7. Assemble the Drive case.

6-52

ASSEMBLING THE DRIVE CASE

1. Carefully position the tophousing onto the base

and coverplate.

2. Install and tighten the four screws (#6-3/4”

SHTMTL, PHIL HD.) securing the tophousing to the
coverplate. Install the screw hole covers.

3. Refer to the final checkout section of this

manual and complete the full checkout procedure
for the Drive.

6-53

ADJUSTMENTS

7-1

READ/WRITE & ERASE HEAD CLEANING & DEMAGNETIZATION

Both the head and the pressure pad will accumulate
dirt and oxide particles during use. Periodic
cleaning and inspection is necessary for proper Disk
Drive operation.

CAUTIONS: The head is subject to magnetization from
external fields. DO NOT use magnetized tools or allow
the head to get near any equipment producing strong
magnetic fields.
DO NOT lift the pressure pad arm farther from the
head carriage than the arm would be lifted during
normal Disk Drive operations (i.e. front door open).

1. Use a small mirror to inspect the pressure pad

for excessive buildup of oxides and dirt, or for
excessive wear. Replace the head if it is worn or
damaged.

2. Otherwise, clean the head.

NOTE: Use either a cotton swab (preferred) or a lint­free cloth (if. chamois) moistened with either methyl
or high quality 31% isopropyl alcohol.
Wipe the head carefully to remove all accumulated
oxide and dirt. Dry the head.
CAUTION: DO NOT use carbon tetrachloride as a
cleaning solution for the head.

7-2

3. To demagnetize the head, hold the energized

demagnetizing tool about 6 inches above the head.
Slowly lower the tool toward the head in a
spiraling motion. DO NOT allow the tool to come
into contact with the head.

4. Reverse the procedure as you lift the tool away

from the head. DO NOT turn the tool off until it
is at least 6 inches away from the head.

7-3

RADIAL TRACK ALIGNMENT & SPEED ADJUSTMENT

Radial track alignment and speed adjustment is
necessary to provide optimum diskette compatibility
between Drives.
The following are required to perform this procedure:

A. Oscilloscope, dual trace with A+B function, and B

invert function, with two probes.

B. Atari 400/800 Computer Console with minimum 16K

RAM installed.

C. I/O cables and Console/Drive power packs.
D. Disk Alignment Cartridge or Program.
E. Master Alignment Diskette.
F. 0.050 hex setscrew driver.
G. Non-conductive common blade tuning wand.

CAUTIONS: Take extreme care when handling and storing
the master alignment diskette.

The Disk Drive PWR ON lite should be ON and the BUSY
lite should be OFF whenever you are inserting or
removing a diskette from the unit. DO NOT open the
Drive door or turn Drive power off when the BUSY lite
is on.

7-4

1. Connect the Drive to the Computer Console.

2. Turn the Drive on and wait for the BUSY lite to

go off. Insert the master alignment diskette.

3. Either insert the disk alignment cartridge or

load the disk alignment program into the Console.

4. Via the Console, command the Drive to read track

#16.

5. Set the oscilloscope controls as follows:

DISPLAY: A + B, B inverted
TIME/DIV: 20msec./DIV
VOLTS/DIV: 20mV/DIV

6. Compensate your scope probes.

7. Connect a ground probe from the scope to the

faston lug ground at the rear of the transport.

8. Attach the channel A probe to the rear lead of

CR154.

9. Attach the channel B probe to the rear lead of

C155.

7-5

CAT’S-EYE PATTERN

10. The ’scope should be displaying a repeating

cat’s-eye lobe pattern as shown above.
a. If the lobes are of equal amplitude, goon to

step 11.

b. If the lobes are of unequal amplitudes,

proceed as follows:

1. Locate the setscrew securing the stepper
motor positioning band pulley to the stepper
motor shaft.

2. With the Drive still reading track 16, back
the setscrew out (counterclockwise) of the
pulley about l/4 turn. Leave the setscrew
driver in the pulley.

3. Slightly rotate the pulley either clockwise
or counterclockwise until the ’scope shows
equal amplitude cat’s-eye lobes.

4. Tighten the setscrew and remove the setscrew
driver.

5. Verify that the lobes are still within 80%
amplitude of each other. If they are not,
return to step 2.

6. Via the Console, command the Drive to step
back to track 00 and return to read track 16.

7-6

"CAT’S EYES" DISPLAY AS A FUNCTION OF READ HEAD to

TRACK 16 POSITION

7. Verify that the lobes are still within 80%
amplitude of each other. If they are not,
return to step 2.

8. Via the Console, command the Drive to step
out to track 32 and return to read track 16.

9. Verify that the lobes are still within 80%
amplitude of each other. If they are not,
return to step 2.

NOTE: Steps 6 thru 3 check the hysteresis within
the head positioning system. If you are unable to
achieve the results indicated, suspect: 1) a broken
or damaged setscrew; 2) a binding and misaligned
positioning band; 3) binding of head assembly to
guiderods; or 4) a bad stepper motor.

11. Disconnect the ’scope probes (except for the

ground lead) from the drive circuit.

12. Reset the ’scope DISPLAY to channel A only.

13. Attach the A channel probe to ANODE side of CR110

(tachometer output).

7-7

14. Command the Drive to read any track.

15. Refer to the following guide for correct

tachometer frequencies. If the tested frequency
is not correct, adjust R142.

7-8

DRIVE

BELT

Mylar
(yellow)
Mylar
(yellow)
Neoprene
(black)

SPEED ADJUSTMENT GUIDE

DRIVE MOTOR

PULLEY

TACH

FREQUENCY

ONE CYCLE

TIME

DIAMETER

.250” 390 Hz 2.564 msec 3-35003-002

.300” 320 Hz 3.125 msec 3-35003-001

.300” 305 Hz 3,279 msec 3-35003-001

DRIVE
MOTOR

PART NO.

7-9