1050 Disk Drive

Field Service Manual 2

 TABLE OF CONTENTS

Section Title Page

1 THEORY OF OPERATION 5
Overview 5
Operator Functions 6
Front Panel 8
Back Panel 9
Mechanical Theory 9
Case 9
Drive Mechanism 10
Head Carriage Assembly 10
Drive Motor 10
Stepper Motor 10
PCB Assembly 10
Power Supply 10
Power-Up Logic 11
Electronic Theory 11
6507 Microprocessor Unit (Microprocessor) 12
6532 Peripheral Interface Adaptor (PIA) 12
2793 Floppy Disc Controller (FDC) 13
Clock 14
Read-Only-Memory (ROM) 14
Random Access Memory (RAM) 14
Write Erase Logic 14
Write Protect Logic 15
Read Logic 15
Read/Write Head 16
Erase Head 16
Serial Bus Line Assignments 17
Line Assignments 17
Serial Bus Electrical Specification 17
Serial Bus Protocol 18

2 1050 SPECIFICATIONS 19

3 DISASSEMBLY/ASSEMBLY 21

4 DIAGNOSTIC TESTINGS 22
Equipment Requirements 22
Hook-Up 22
Check of Mechanical Components 22
Diagnostic Tests 22
Power-Up Tests 22
Loading the Diagnostic Test Diskette 23
MPU & Controller Test 24
Invalid Command Test 24
Write Protect Test 24
Motor Start Test 24
Motor Speed Test 24
Head Step & Settle Test 25
Track 00 Test 25
Loop on Speed Calibration 26
Run Manual Alignment Tests 26
Drive Select Switch Test 28

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 Single Density Burn-in (10 min.) 28
Double Density Burn-in (2 hours) 29
Track 00 Sensor Calibration 30

5 SYMPTOM CHECKLIST 31

6 WAVEFORMS 36
Motor Control Signals 36
Tach Feedback Signals/Speed Adjustment 37
Stepper Drive Signals 37
Diskette Enable Signals 38
Track 00 Signals 38
Data-In Signals 38
Read Signals 39
Write Signals 40
Write Gate Signals 40
Erase Gate Signals 41
Erase Signals 41
Clock Signals 42
Write Protect Signals 42
Power Supply Signals 43
Data Out Signals 44
Command Signals 44
Vcc/Ready Signals 44

7 SCHEMATICS AND SILKSCREENS 45

8 PARTS LIST 51

List of Illustrations

Figure Title Page

1 Simplified Block Diagram 5

2 System Hook-Up 6
3 Atari 1050 Disk Drive Control/Indicator 7
4 Exploded Diagram of the Disk Drive 9
5 Power Supply Block Diagram 10
6 Disk Drive Electronic Units 11
7 Write/Erase Logic Block Diagram 15
8 Read Logic Block Diagram 15
9 Erase Head Gaps 16
10 PERIPHERAL Connector 17
11 1050 Drive Mechanism (TANDON) 21
12 Plug Connections of 1050 Mechanism 21
13 1050 Disk Diagnostic Screen 23
14 Running 1 Option… 24
15 Running 1 Option (continued) 25
16 Troubleshooting Options List 25
17 Motor Speed Test 26
18 Cat-Eyes Waveform 27
19 Head Azimuth Waveforms 28
20 Example 1 of Error Printout 29
21 Example 1 of Error Printout 29
22 Track 00 Sensor Calibration Test 30

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 SECTION 1
THEORY OF OPERATION

OVERVIEW

The ATARI 1050 Disk Drive is a record/playback device that allows information to be stored and
retrieved quickly and accurately. The actual recording is much like a tape recording process and is done on
similar material. The data is magnetically recorded on a 5.25 inch diameter diskette. Each diskette can
store 88K bytes of data in single density mode and 133K bytes in double density, however double density
can only be implemented in conjunction with DOS 3. The diskette is inserted through a door in the front
panel of the drive unit. The 1050 Disk Drive is used with a single ATARI 400, 800 or 1200 Computer
with a minimum of 16K of RAM installed.

Figure 1 is a simplified block diagram of the functional flow of the 1050 follows. Each of its functional
units are explained in greater detail below.

1 3 4
MPU 5
ROM
CMD RAM
STAT FDC ANALOG READ/WRITE &
LOGIC ERASE HEAD
DATA
PIA

DRIVE MOTOR
6
STEPPER MOTOR

Figure 1. Simplified Block Diagram

Block 1 Includes the Data Input/Output (I/O) connectors. They are the origin and destination of all
commands, status and data.
Block 2 Includes the Microprocessor(MPU), Read-Only-Memory (ROM), Random Access Memory
(RAM) and Peripheral Interfaces Adaptor (PIA). They process all commands and control data
flow to and from the console.
Block 3 Includes the 2793 Floppy Disk Controller (FDC). The FDC controls data flow to and from the
diskette.
Block 4 Includes the Analog Logic. The Analog Logic processes all data to and from the Read/Write
Head.
Block 5 Includes the Read/Write and Erase Head.
Block 6 Includes the Drive Motor and Stepper Motor which are located in the Drive Mechanism. They
receive signals from PIA.

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OPERATOR FUNCTIONS

Each 1050 Disk Drive comes with an AC Power Adaptor and a Data Cord. Figure 1-2 shows how to
connect the Disk Drive and computer console.

Figure 2. System Hook-up

The Controls/Indicators are located on the front and back panels of the 1050. The front panel of the
1050 contains the Activity Light, the Power Indicator Light, the Power ON/OFF switch, and the door
latch. The rear panel of the 1050 contains the Input/Output (I/O) connectors, Power-Jack and Drive
Code Switch. (Use Atari 810 switch settings to identify drive number 1,2,3 or 4).

These functions are illustrated in Figure 1-3 and discussed in the following paragraphs.

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 Figure 3. ATARI 1050 Disk Drive Control/Indicators

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Front Panel
The Activity Light lights whenever the drive is reading from or writing to a diskette or when the diskette
is first inserted, and the door latch turned down. DO NOT OPEN THE DRIVE DOOR, TURN
POWER OFF, OR ATTEMPT TO REMOVE THE DISKEETTE WHEN THE LIGHT IS ON!
The Power Indicator lights whenever power to the Drive is ON.
The Power ON/OFF switch is a toggle switch pushed to the right for ON, and to the left for OFF.
ALWAYS insert or remove diskette with Power ON.
The Door Latch turns down to close the door after a diskette is inserted. The Activity Light then lights
for a few seconds. The latch turns parallel to the diskette slot for removing the diskette.
Back Panel
The Input Output (I/O) connectors are identical jacks for the data cords from the computer console or
ether peripheral devices. Connections may be made in any other with either jack.
The Power Jack accepts the AC Power adaptor.
The Drive Code Switch is a 4 - position switch that tells the computer which drive it is communicating
with.
Two switches (one black and one white are visible in the rectangular opening on the drive rear panel.
Using a pen or screwdriver, move the switches to the correct position on each drive being used.
Drive Code Number Diagram shows the correct positions of the Drive Code Switch to set the
identification of the Drive (1 thru 4).

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 MECHANICAL THEORY

The 1050 unit is compose on an outer case which houses the Driver Mechanism, Drive Motor, Head
Carriage Assembly, Stepper Motor and PCB.

CASE

The 1050 outer case consists of three pieces of plastic.

Figure 4. Exploded Diagram of the Disk Drive

Figure 1-4 illustrates the mechanical elements of the 1050 unit are discussed in the following paragraphs.

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DRIVE MECHANISM
The Drive Mechanism provides mechanical and electronic linkage to the diskette. It is the physical
assembly containing the Head Carriage Assembly, Drive Motor, Stepper Motor, and Write Protect
sensor, Track 00 sensor, and Diskette Enable switch.
HEAD CARRIAGE ASSEMBLY
The Head Carriage assembly allows the head to be cycled across the diskette. It contains the Read/Write
and Erase Head, the pressure pad and springy assembly.
DRIVE MOTOR
The Drive Motor is a DC motor which indirectly drives the diskette. It is attached by a drive belt to a
flywheel which rotates the disk.
The DC motor includes an internal Tachometer, whose output is monitored in the Tach Feedback
circuit. The Tach Feedback circuit senses changes in current and maintains a constant motor speed.
The activity Light (LED) comes on whenever the motor turns on.
STEPPER MOTOR
The Stepper Motor positions the head over a desired track. It is a four-phase motor. Each change in
phase rotates the Stepper Motor shaft. This circular motion is converted to Linear motion by the
positioning band/pulley assembly which links it to the head carriage.
The Stepper Logic is controlled by the PIA Chip. Four PIA, signals act as the Stepper Motor's four-
phase inputs. These lines in various combinations, drive the Stepper Motor to reposition the Head
Carriage Assembly from track to track.
PCB ASSEMBLY
All of the digital and analog logic for the 1050 is contained on one PCB.

POWER SUPPLY
The Power Supply provides the following voltages for use in the system:
• +5V DC regulated, which provided the voltage for the logic and for the 2793-02 Floppy Disk
Controller,
• +12V DC (regulated), which feeds to Stepper Motor, Drive Motor, Zero Crossing Detector,
Read/Write and Erase circuitry, and Tach feedback.

Figure 5. Power Supply Block Diagram

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The 120V AC (or 230V AC) which comes into the system is stepped down to 9V AC by an external
transformer (See figure 1-6).
The 9V AC is applied to the bridge rectifier on to PCB when the Power ON/OFF switch is turned ON.
An internal 2A fuse in the adaptor provides current limiting protection.
POWER-UP LOGIC
The Disk Drive’s Power-up logic resets the 6707 microprocessor, Stepper Motor logic, Peripheral
Interface Adaptor (PIA) and Data Interface section (2793 FDC and Analog circuitry) whenever the drive
is turned on. In addition, the power-up logic circuit locks the Data Output Buffer off during the short
period when the drive is tuned on. This prevents random pulses generated by the drive’s circuitry (during
the initialization period) from being sent to the console.
The RESET logic returns the electrical circuits to their starting conditions.

ELECTRONIC THEORY

The 1050 Disk Drive consists of eight major electronic elements. These include:
• Power-up logic (discussed in the Power Supply section above)
• Clock
• 6507 Microprocessor Unit (MPU)
• Read-only Memory (ROM)
• Random Access Memory (RAM)
• 6532 Peripheral Interface Adaptor (PIA)
• 2793 Floppy Disk Controller
• Read/Write and Erase Logic

Functional block diagram of the electronic elements of the 1050 Disk Drive follows (Figure 1-6), along
with a discussion of each.

Figure 6. Disk Drive Electronic Units

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6507 MICROPROCESSOR

The Disk Drive's 6507 microprocessor (MPU) provides the primary decision making and computational
capabilities for the drive. It is a self-contained microcomputer system on a single chip.

The MPU controls the sequence of system operations by putting addresses out to the program memory
(ROM) and receiving instructions in return. It causes the system to perform the desired operation by
reading an instruction (specific bit pattern) and executing that instruction. It then goes to the next
instruction in the program and executes it.

The microprocessor:

• Controls the 2793 or 2797 Floppy Disk Controller (FDC)

• Monitors the Peripheral Interface Adaptor (PIA) for data transfers and status requests by the
computer console.
• Controls the Stepper Motor Logic, Disk Drive Logic and Motor Logic, all of which are buffered
in the P IA.
• Provides control characters to notify the computer console of the status of operations performed
and information received.
• Executes commands from the computer console.
• Controls data transfers through control of the common data and address buses.

The address bus, the bi-directional data bus, and the Read/Write line serve as parallel paths for data
transfer in end out of the microprocessor and give it direct control over the central processing system.
The address bus puts out addresses to control the source or destination of data transfers. The Read/Write
line determines the direction in which data transfer occurs.

These addresses are derived from various sources within the microprocessor. During the instruction cycle
from program memory (ROM), the addresses are usually derived from the program counter which
controls the execution of sequential instructions. Addresses for data transfers between the microprocessor
and RAM are usually derived either directly from the program memory or from the microprocessor.

6532 PERIPHERAL INTERFACE ADAPTOR (PIA)

The 6532 Peripheral Interface Adaptor (PIA) is a buffering and signal: formatting device with no decision
making or computational capability. It is an Input/Output ( I/0) device which acts as an interface between
the 6507 microprocessor, the 1050 system functions and the console.

The PIA

• Monitors the 2793 or 2797 Floppy Disk Controller.

• Provides 128 bytes of RAM for temporary store of status information and data sent by the Data
Interface section for application to the microprocessor.
• Applies the console's serial outputs to the data and address buses when requestd to do so by the
drive's microprocessor unit.
• Acts as communication interface between the computer console and the microprocessor.
• Interfaces with the Stepper motor Logic and Drive Motor Logic.

The microprocessor communicates with the PIA through eight data lines connected to the data bus. The
microprocessor initiates communication by using its address lines to select or address the P IA.

The PIA provides 16 programmable bi-directional port lines to communicate with the computer console
and perform the system functions. The port lines are divided into two 8-bit ports, PAO-PA7 and PBO-
PB7. PA7 may also function as an interrupt input pin.
The Interrupt Request ( IRO) line is used to inform the microprocessor when a device requires servicing.

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2793 OR 2797 FLOPPY DISK CONTROLLER

The 1050 disk drive will contain either a 2793 or 2797 Floppy Disk Controller IC depending on the date
of manufacture of the drive.

The 2793 or 2797 Floppy Disk Controller (FDC) and the Read/Write and Erase Logic make up the Data
Interface between the disk drive's central processing system and the diskette. Pin 25 of 2797 should be out
of socket.

The FDC is the main element of the Data Interface function. The FDC is a highly specialized
microprocessor which has an arithmetic logic unit, comparator and the necessary microprogram logic to
control the Read/Write operation to the diskette. It also includes an internal phase-lock loop, data
separation and write precompensation logic.
The FDC:

• Combines data, timing and data validity pulses into the serial format for recording onto diskette.
• Separates the above signals and provides the output data in parallel during a Read operation.
• Controls the Write and Erase logic circuitry during a Write operation.
• Generates the data validity codes (called Cyclic Redundancy Checks or CRCs) during a Write
operation and checks them during a Read operation.
• Contains an internal phase-lock loop.

The microprocessor controls the FDC and can access any of the following registers located in the FDC:
Track, Sector, Data, Command, and Status. The following is an explanation of the contents of each
register.

Track Current head address. Updated automatically as the head moves across the diskette.
Sector Number of the sector being considered for a Read or Write operation.

Data Information read from the diskette to be transferred to the microprocessor after the necessary
serial-to-parallel conversion. The FDC receives data in parallel from the microprocessor and converts the
data to serial for storage on the diskette.
Command Instructions from the microprocessor that are interpreted by an internally controlled
programmable logic array to generate the appropriate control signals for the logical operation to be
performed.
Status Condition of the system. After each command is executed, the control logic issues an interrupt to
the microprocessor to allow examination of the status register for any errors before resetting the interrupt.
Each of the eight bits in the status register represents a different error condition.

The FDC controls the following elements of the Data Interface function:

• Read/Write Head
• Erase Head
• Read Logic
• Write/Erase Logic
• Write Protect Logic

CLOCK

The clock generator produces a continuous waveform that controls all signal transitions in the system. It
provides timing controls for the 1050 Disk Drive Logic and the Read/Write operations to the diskette.

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The drive's clock circuitry generates a crystal controlled 1 MHz signal. The 1 MHz signal is used by the
2793 or 2797 Floppy Disk Controller (FDC) and Write/Erase gate for timing serial data to the heads. It is
also used by the 6507 microprocessor to clock parallel data into and out of the FDC.

READ-ONLY MEMORY (ROM)

The Disk Drive's Read-Only Memory (ROM) stores the sequence of instructions (program memory) that
make up the 1050's internal control software. It contains specific operating instructions used by the
microprocessor to accomplish a variety of functions. These functions include telling the 2793 or 2797
Floppy Disk Controller (FDC) what task to perform.
An important characteristic of the ROM chip is that the information is stored on a permanent basis.
Turning OFF the power does not cause the loss of ROM information.

RANDOM ACCESS MEMORY (RAM)

The Disk Drive's Random Access Memory (RAM) is used by the microprocessor for temporary storage of
Input data, calculations and system information.

Data may be written into RAM as well as read from RAM by the microprocessor. The RAM Identifies the
type of data transfer by the Read/Write line. When the line is active HIGH, the operation is to Read from
memory and when the line is active LOW, the operation is to Write to memory. Turning the power OFF
obliterates all information in RAM.

WRITE/ERASE LOGIC

The Write/Erase Logic manages the recording of data from the Floppy Disk Controller to the diskette. It
provides correct current and polarity to the Read/Write Head.
The Write Driver enables Write functions and limits the Write currents.
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.

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 STATUS
WRITE
PROTECT
DATA TIMING

DATA BUS FDC

WRITE GATE
ADDRESS WRITE
BUS WRITE DATA DRIVER
WRITE
AND ERASE
RESET GATE

ERASE
DRIVER
+5V
TIME
DELAY
FILTER ERASE READ/WRITE
HEAD HEAD

Figure 7. Write/Erase Logic Block Diagram

WRITE-PROTECT LOGIC

The Write-Protect Logic prevents writing to a diskette by informing the Floppy Disk Controller when a
write-protected diskette is inserted in the drive. Each diskette contains a notched area in the upper right
hand corner which allows light from the LED to hit the base of the phototransistor. On a write-protected
diskette the light is blocked by a tab or opaque material on the diskette. This turns off the phototransistor
and the output from U11 is clamped Low. The low input to the FDC signals that a write-protected
diskette is inserted and you cannot write to it.

READ LOGIC

The Read Logic is used to retrieve data from the diskette and input the data into the FDC. It shapes
pulses into the correct format to be read by the FDC.

STATUS PHASE PULSE TIME DELAY

LOCK GENERATOR FILTER
LOOP
DATA TIMING

ZERO
DATA BUS FDC DIFFERENTIATOR CROSSING
DETECTOR

ADDRESS
BUS DIFFERENTIAL READ/WRITE
AMPLIFIER HEAD

Figure 8. Read Logic Block Diagram

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The DIFFERENTIAL AMPLIFIER provides initial amplification of READ/WRITE HEAD signals.

The DIFFERENTIATOR squares up the two DIFFERENTIAL AMPLIFIER outputs.

The single output Zero Crossing Detector changes level whenever the two 180 degree out-of-phase input
signals cross their zero axis coincidentally. This eliminates false pulses caused by READ/WRITE HEAD
signal decay, rather than intentional signal level changes.

The TIME DELAY FILTER is a digital filter.

The PULSE GENERATOR produces a single pulse out for each logic level transition at its output. This
results in the reproduction of the original FDC signal.

READ/WRITE HEAD

The READ/WRITE HEAD is an electro-magnetic device used for interfacing with the magnetic
recording media. It converts magnetic flux changes to electric current, and vice versa, through the use of a
center tapped coil.
Current is passed through the windings on the head core. Data is written to the diskette surface by
changing the direction of the current through the READ/WRITE HEAD (each flux change equals a data
bit).
Data is read from the diskette when signals from the head coil windings are applied to the differential
amplifier.

ERASE HEAD

The ERASE HEAD creates a guardband (a blank space between tracks) in order to prevent one recorded
track from interfering with either the next inner or next outer track.
It straddles the Read/Write Head in such a way that after the data is written onto the diskette, the Erase
Head "tunnel" narrows the track width, leaving guardbands between tracks.

Track 18 Disk rotation

ERASE
Guard Band HEAD
GAP READ/

WRITE
Track 17
HEAD
ERASE
GAP
HEAD
Guard Band GAP

Track 16 Disk rotation

Figure 9. Erase Head Gaps

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SERIAL BUS LINE ASSIGNMENTS

The computer communicates with peripheral devices via a serial port which consists of a serial DATA
OUT (transmission) line, a serial DATA IN (receiver) line and miscellaneous control lines.

Data is transmitted and received as 8 bits of serial date (least significant bit sent first) preceded by a logic
zero start bit and succeeded by a logic one stop bit. The serial DATA OUT is transmitted as a positive
logic ( +4V = one/true/HIGH, 0V = zero/false/LOW). The serial DATA OUT line always assumes its
new state when the serial CLOCK OUT line goes HIGH; CLOCK OUT then goes LOW in the center of
the DATA OUT bit time.

2 4 6 8 10 12
o o o o o o
o o o o o o o
1 3 5 7 9 11 13

Figure 10. PERIPHERAL Connector

1 CLOCK IN is not used by the current DOS and peripherals. This line is reserved for future
synchronous communications.
2 CLOCK OUT is the serial bus clock. CLOCK OUT goes HIGH at the start of each DATA
OUT bit and returns to LOW in the middle of each bit.
3 DATA IN is the serial bus data line to the computer.
4 GND is the signal/shield ground line.
5 DATA OUT is the serial bus data line from the computer.
6 GND is the signal/shield ground line.
7 COMMAND is normally HIGH and goes LOW when a command frame is being sent from the
computer.
8 MOTOR CONTROL is the cassette motor control line (HIGH = on, LOW = off).
9 PROCEED is not used by the current DOS and peripherals. This line is pulled HIGH passively
inside the computer.
10 +5V/READY indicates that the computer is turned on and ready. This line may also be used as a
+5 volt supply of 50liA current rating, for Atari peripherals only.
11 AUDIO IN accepts an audio signal from the diskette.
12 +12V supply for Atari peripherals only (not used in 1050).
13 INTERRUPT is not used by the current DOS or peripherals. This line is pulled HIGH passively
inside the computer.

SERIAL BUS ELECTRICAL SPECIFICATIONS

Peripheral Input:

VIH = 2.0 V minimum

VIL = 0.4 V maximum

I IH = 20 µA maximum at VIH = 2.0V

IIL = 5 µA maximum at VIL = 0.4V

Peripheral Output (open collector bipolar):

VOH = 4.5 V minimum with external 100 kΩ pull-up

VOL = 0.4 V maximum at 1.6 µA

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Vcc/READY Input:

VIH = 2.0V minimum at IIH = 1 µA maximum

VIL = 0.4V maximum
Input goes to logic zero when open

SERIAL BUS PROTOCOL

When a command line goes LOW, the computer console sends a command frame to all devices. The
command provides the disk drive with the following information:

• Serial Bus Device ID

• Command
• Two bytes of auxiliary information
• Checksum

The commands suppported by the disk controller are: Get Sector, Put Sector, Put Sector with Verify,
Status Request, and Format Disk.

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 SECTION 2
1050 SPECIFICATIONS

Functional Specification

Key Features

• Lower Cost than 810.

• Fully compatible with 810 in single density (FM) mode.
• Double Density read/write operation using MFM encoding.
• Fully compatible with existing Atari disk operating system.
• Fully support the Atari SIO interface and protocol.
• Support new high level macro command requested by next generation Atari disk operating
system.

Disk Drive Specification

Single Density Double Density

(Read/Write) (Read/Write)
Tracks per surface 40 40
Tracks per inch 48 48
Recording Density (track 39) 2,878 BPI 5,757 BPI
Flux Density (track 39) 5,757 FCI 5,757 FCI
Encoding Method FM MFM
Capacity unformatted:
Per Track 3,382 Bytes 6,510 Bytes
Per Surface 135,280 Bytes 260,400 Bytes
Capacity formatted:
Sectors/Track 18 26
Bytes/Sector 128 128
Bytes/Track 2,304 3,328
Bytes/Surface 92,160 133,120

Transfer rate 125,000 BPS 250,000 BPS

Read/Write Head 1 1
Write Protect Sensor Yes Yes
Track 00 Sensor Yes Yes
Rotational Speed 288 RPM 288 RPM
Rotational Speed Accuracy ± 3% ± 3%
Average Latency 110 ms 110 ms

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 Single Density Double Density
(Read/Write) (Read/Write)

Access Time (max):

Track to Track 40 ms 40 ms
Head Setting 30 ms 40 ms
Motor Start 1000 ms 1000 ms

Media Requirements:

Single Density: Soft Sectored, per Atari specification (#CO16884)

Double Density: Soft Sectored, per Atari specification (#CO16890)

Physical and Dimensional Specification:

Drive outside dimension (exclusive of front panel)

HEIGHT 1.70 inches max.

WIDTH 6.00 inches max.
LENGTH 8.00 inches max.
WEIGHT 6 Pounds max.

Electrical Specification:

Drive Read/Write Electronics

Head Voltage at 1F amplitude 10 mV max. at Track 00

Head Voltage at 2F amplitude 3 mV max. at Track 39

These data values should be obtainable from various diskette vendors.

Power Specification:

AC Power Adaptor (North America Version):

Consult the Atari 31 VA AC Power Adaptor Specification (# CO17945)

AC Power Adaptor (International Version) TBD

System Electronics
Including Drive Electronics, Controller Electronics and Power Supply Electronics:

Input Voltage 8.52V AC ±12% @ 60Hz ±3Hz

Power Consumption:

Standby 15 W max.
Operating 30 W max.
Start Up 50W max.

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 SECTION 3
DISASSEMBLY/ASSSEMBLY

Turn the unit over and remove the four screws from the bottom cover and the two screws holding the
lower part of the front bezel (see figure).
Holding the top and bottom covers together, turn the unit right side up.
Carefully pull the lower part of the front bezel forward and at the same time lift off the top cover. (Be
careful not to break the thin plastic tabs attaching the top of the front bezel to the top cover).
The drive mechanism rests on four dowels above the Printed Circuit Board. To remove it, disconnect the
plugs from the PCB and lift it out. When reattaching, be sure to note the correct polarity of the plugs (see
figure).
The PC board snaps into the bottom of the lower cover and fits over the three alignment guides located in
it.
The upper and lower RF shields are attached to the PCB by four bend tabs. When removing the top
shield, be sure to note where the cutouts are located and replace it the sane way.
The five LSI's are located under the shield No adjustment to the variable capacitor or resistors is needed
when replacing the 2793 or 2797 Floppy Disk Controller chips.
Reassemble in the reverse order.

Figure 11. 1050 Drive Mechanism (Tandon)

J1 1
J6 0
J10 1
J11 1
J12 1
J14 1
J15 1

Figure 12. Plug Connections of 1050 Mechanism

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 SECTION 4
DIAGNOSTIC TESTINGS

Equipment Requirements:

• 400 Computer with 16K of RAM

• Television
• Oscilloscope at least 15MNz Digital Voltmeter
• ATARI 1050 Disk Drive Diagnostic Diskette (FD 100690)
• Dymek Alignment Diskette (TEO 17575)
• Work Diskette (FD 100053)
• Preformatted Diskette( FD 100026)
• Assorted Small Tools
• Printer (Optional)

Hook Up

• Set up the disk drive and computer according to the procedures in the 1050 Owner's Guide.
• Set the drive select switches to the Drive 1 position.
• Be certain all connections ere secure.

Check Of Mechanical Components:

• Before testing the Disk Drive, be certain of the following:

• Check that the diskette enable lever moves freely and locks in the perpendicular position.
• Insert a diskette in the slot and push it all the way in. Make sure that the eject mechanism clicks
into position. Now move the diskette enable lever around to the perpendicular position to lock.
Make sure that the diskette is ejected when the diskette enable lever is returned to the parallel
position.

Diagnostic Tests

The tests in this section are intended to assist you in diagnosing possible problems in the 1050 Disk Drive.
All diagnostic and functional tests are reviewed in this section. Use these tests in conjunction with the
troubleshooting guide, waveform diagrams, and schematics to troubleshoot the unit under test.

Power Up Test

Purpose: To test the disk drive's electronic hardware Initialization and Reset. This test
prepares the drive for further testing. The drive must pass this test before any
other tests can be performed.

Special Tools Required: None

Procedure:

1. Connect disk drive to computer.

2. Turn the disk drive power switch ON.
3. Observe that the following occur:
a. The Power LED lights.
b. The Activity LED lights.
c. The Drive Motor turns on.

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Field Service Manual 22
 d. The Head Carriage steps to track 00 (outer track).
e. Several seconds pass, and the Drive Motor and the Activity LED turn off.
4. This completes the Power-up Test.

This test indicates that the unit passed all of its internal diagnostics. The internal diagnostic test checks the
following six elements:

1. Input/Output Device
The 6532 device is initialized and verified. Upon incorrect comparison, the
processor will flag ERROR.
2. Disk Controller Device
The 2793 or 2797 device is tested for ass to the track, and sector registers, followed
by an internal functional test. Upon error, the processor will flag ERROR.
3. ROM Checksum
The processor verifies PROM validity by performing a checksum on it. Upon error,
the processor will flag ERROR and discontinue testing.
4. RAM Check
Unique values are written to each RAM location, and then each location is read to
verify It contains the correct value. Upon error, the processor will flag ERROR and
discontinue testing.
5. Error Flag Stop
Upon any ERROR flag being set, the processor will discontinue testing and place the
unit in a hard failure state (2-second cycle off/on of spindle motor).
6. Restore Check
Track 0 is sought by stepping the head away from spindle until track 0 sensor is
detected and motor phase is 1. Upon stepping more than 50 tracks without finding
the track 0 sensor, the unit will fail and enter the hard failure state.

Loading The Diagnostic Test Diskette

Insert the Diagnostic Diskette and turn the diskette enable lever down. The activity LED lights, and the
motor spins for about five seconds, centering the diskette on the spindle.
Now Power-Up the computer without a cartridge installed The Diagnostic Test will boot-up and display
the two main menu options on the TV screen.

Figure 13. 1050 Disk Diagnostic Screen

Make selection 1 and hit the RETURN key. The diagnostic testing will run automatically.

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Field Service Manual 23
 Figure 14. Running 1 Option…

These pass or fall tests will indicate which section of the disk drive to start your troubleshooting in. The
following is a detailed description of each test.

MPU & Controller Test

This checks that the 2793 or 2797 floppy disk controller chip will recognize a command or data frame
from the computer. A failure here indicates a defective 2793 or 2797 IC.

Invalid Command Test

This checks that the 2793 or 2797 floppy disk controller chip .will recognize an illegal command or data
frame and not try to execute on it.

Write Protect Test

This checks out the Write Protect Sensor and related circuitry.
* If Write Protect is constantly on, check to be sure that dirt has not blocked the hole where the lower
part of the sensor is located.

Motor Start Test

This test checks the elapsed time between starting the spindle motor from a dead start to the point where
valid data is read from the diskette. If this test fails a motor control circuit or a read circuit failure is
indicated.

Motor Speed Test

This test checks the speed of the spindle motor in milliseconds. If the speed is too low or too high use the
speed calibration option in the troubleshooting section of the Diagnostic Program Disk to adjust (VR2)
with a screwdriver.

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Field Service Manual 24
 Figure 15. Running 1 Option (continued)

Head Step & Settle Test

This test checks the capability of the drive to read a sector, step to the next track, ark read another sector
within a specified amount of time. A failure here would indicate a bad drive mechanism, or a defect in the
read circuitry.

Track 00 Test

This test steps the Read/Write Head out to track 02 then steps back to track 00 and checks the status of
the track 00 sensor. If this test fails, use the track zero sensor calibration option in the troubleshooting
section of this diagnostic program to adjust the sensor.
At the end of the Diagnostic tests, you are again given the choice of:
(1) Run Diagnostic Tests
(2) Troubleshooting Options
Select 2 and hit RETURN. This will give you the troubleshooting options menu.
This section combined with the troubleshooting guide, circuit waveforms, and schematics, will help you to
troubleshoot or make adjustment to various circuits in the 1050 disk drive.
Read the instructions and follow the prompts, displayed on the screen, carefully.
The following is a detailed description of the troubleshooting options:

Figure 16. Troubleshooting Options List

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Field Service Manual 25
Loop on Speed Calibration
Use this option to set the spindle speed.

Figure 17. Motor Speed Test

Adjust VR2 for a speed of 208.3 milliseconds ±1.0 msec.

Run Manual Alignment Tests

The following four tests are designed to check out the drive mechanism alignment. Use the Dymek
Analog Alignment Diskette (Part # TE017575).
Set the oscilloscope as follows:
Channel A Normal
Channel B Inverted
Vertical Mode Add. Ch. A&B
Time/Div 2ms/Div
Volts/Div 20mV/DIv (X10 Probes)
AC (Ch. A&B )
Trigger Internal (Ch A), AC, Normal,
Positive slope
Set up the probes as follows:
Channel A TP 3 on PCB A
Channel B TP 4 on PCB A
Ground TP 17 on PCB A

Use track 0 to double check the spindle speed of the drive mechanism on track 00. The time for one cycle
of the sinewave is approximately 16.6ms.
Use track 16 to check or adjust the radial track alignment.
(Cats-Eyes). Set the time/div at 20ms/Div and follow the instructions below.
Verify that cats-eyes lobes are present on the oscilloscope and observe the lobe ratio of the cats-eyes. The
lobe ratio is the amplitude of the smaller lobe divided by the amplitude of the larger lobe. The ideal lobe
ratio is 100% (both lobes equal). See figure below.

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Field Service Manual 26
 Figure 18. Cat-Eyes waveforms

Align the TM50-1 drive by loosening the screws on the stepper motor and then rotate the motor until the
lobe ratio is 100%. Recheck the track 0 sensor adjustment, then recheck lobe ratio. Repeat until the
alignment is within 80%-100%. Tighten down stepper motor screws.
Use track 33 to check the Head Load Pad Pressure. Set the time/div to 0.5 ms/div, and set the volts/div
to 50 mV/div.
There should be a broadband display on the oscilloscope. With your index finger press very lightly on the
top of the pressure pad. If the amplitude increases greatly (more than 20%) then use a flat blade
screwdriver to turn the pressure pad 1/4 of a turn at a time. After 3/4 of a turn assume the pressure pad
to be bad and replace it.

Use track 34 to check the Head Azimuth. Set the time/div for 0.5ms/div, and set the volts/div for
50mV/div.

See the following diagrams for the correct waveforms.

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Field Service Manual 27
 1 2 3 4 0 minutes of angle

1 2 3 4 -12 minutes of angle

1 2 3 4 +12 minutes of angle

Figure 19. Head Azimuth waveforms

If the Azimuth is greater than ±18 minutes of angle, replacement of the entire drive mechanism is
recommended due to the complexity of the adjustment.

Use the ESC key to stop the test, and the RETURN key to return to the menu.

Drive Select Switch Test

This test is to assure that the disk drive can be selected in all four positions. Check all four positions, then
return to drive #1 position. There is a slight delay and then an automatic return to menu when this test is
done.
If this test fails in any position, check out the switch first, and PIA chip second.

Single Density Burn-in (10 min)

This is a short test to check for compatibility between drives. A failure on this test indicates an alignment
problem. (See Option 2 on troubleshooting options.)
This test first does a write to alt sectors (E5 pattern), then it does a read of all sectors. Be sure to use
preformatted diskette #FD100026.

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Double Density Burn-In (2 hours)
This test formats the diskette in double density, writes and reads all data fields with a sequential seek, and
writes and reads all data fields with an according seek.
Errors are logged into the first and third sector on the track where they occur. These errors can be printed
out on the printer using the printout option in the troubleshooting options of the diagnostic test program.
If the 1050 should be disconnected from the SIO line once this test has been started the testing will
continue until the pass counter reaches zero. This test will abort if:
1. The drive fails to format or verify format.
2. The drive fails to read or write the error logs (sectors 1 or 3 on each track).
3. More than 128 errs occur in any one sector.
6. Error Printout
This option is used in conjunction with the double density burn-in described above to printout the error
logs written on each track.
The following are two examples of this printout and how to interpret them.

1050 BURN-IN (2HR), REV. A

SERIAL I.D. – 3456789012

PASS COUNTER = 0
PASS COUNT RECEIVED = 24
TRACK 31 -ERRORS
SECTOR 16 ERROR STATUS - $01
DATA BYTE LOCATION = 47
DATA DATA DATA DATA SEEK RNF
CRC LOST HARD SOFT
0 0 0 1 0 0

TRACK 31 -ERRORS
SECTOR 20 ERROR STATUS -$02

DATA DATA DATA DATA SEEK RNF

CRC LOST HARD SOFT
1 0 0 0 0 0
TRACK 33 - ERRORS
SECTOR 4 ERROR STATUS = $01
DATA BYTE LOCATION - 77
DATA DATA DATA DATA SEEK RNF
CRC LOST HARD SOFT
0 0 0 1 0 0

Figure 20. Example 1 of Error Printout

1050 BURN-IN (2HR), REV. A

SERIAL ID. - 1234567890

PASS COUNTER = 24
PASS COUNT RECEIVED = 24

NO ERRORS - ALL TRACKS

Figure 21. Example 2 of Error Printout

Example 1 is an example of the error logs which are recorded during the double density burn-in routine.
Example 2 is an example of the printout from a perfect burn-in test.
The use of this error printout is quite subjective. You may have several errors and still have a good drive.
We will attempt to give you a feel for what the major concerns are.
The first thing to look at is the pass counter. This should equal the number in the pass count received,
which indicates that the drive performed burn-in with no major failures.
The next thing to look for is many errors of the same type located on the same track and/or sector. If this
situation occurs, run the burn-in test again using a different blank diskette. If the problem still exists, there
is probably a hardware failure.

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Field Service Manual 29
The next thing to look for is the type of error most commonly found. Below are some clues as to the
cause of the error types:
Data CRC - If several of these errors occur, replace the 2793 or 2797 controller IC. Troubleshoot the
read and write circuits.
Data Lost - This indicates a problem in transferring data between the 2793 or 2797 and the 6810 RAM
IC.
Data Hard - This occurs when data cannot be found after many retries. Check the write circuit and the
diskette for flaws.
Data Soft - This indicates that data was not read on the first pass, but in subsequent passes was found.
If many of these occur in different locations suspect the speed adjustment or 2793/2797.
Seek - Many seek errors would indicate a bad diskette or an alignment problem (cats-eyes).
RNF - Many RNF errors in the same location would indicate a bad diskette. Many RNF errors in
different locations indicates a bad WD2793/2797 controller.
Track 00 Sensor Calibration
This option is used to check and adjust the track zero sensor.
If the sensor is misadjusted, the screen will display either "forward" or "backward" indicating which
direction the sensor needs to be moved. To adjust the sensor, loosen the screw holding it in place and
move the sensor backward or forward as dictated by the screen until the screen displays "sensor OK".

Figure 22. Track 0 Sensor Calibration Test

Be careful ! This is a slight adjustment which does not take much movement to correct. Hold the sensor
in position while tightening down the screw.

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Field Service Manual 30
 SECTION 5
SYMPTOM CHECKLIST

DRIVE MOTOR AND SPEED PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Defective Diskette Enable switch Replace Diskette Enable switch
assembly on drive mechanism.
Intermittent or bad connection Check that P1 is properly
connected to J1
Drive motor doesn’t rotate when Defective diskette enable circuit Troubleshoot and replace
latch is shut (no Activity LED) (U6) defective component (see
waveforms, p. 4-8)
Defective component in motor Troubleshoot and replace
control circuit (Q4, Q6, U5, defective component (see
VR2) waveforms, p. 4-9)
Defective drive motor Replace drive motor
Drive motor operates Intermittent or bad connection Check that P1 is properly
sporadically connected to J1
Defective component in motor Troubleshoot and replace
control circuit (U5, VR2, Q4, defective component (see
Q6) waveforms, p. 4-8)
Defective component in Troubleshoot and replace
tachometer feedback circuit (U5, defective component (see
VR2, Q6) waveforms, p. 4-9)
Open winding in drive motor Replace drive motor
tachometer.
Drive motor speed too slow or Speed adjustment incorrect Adjust speed POT (VR2) for
too fast speed of 208.3 ms
Speed not adjustable Defective component in Troubleshoot and replace
tachometer feedback circuit (U5, defective component (see
VR2, Q6) waveforms, p. 4-9)
Open winding in drive motor Replace drive motor
tachometer.
Drive motor speed unstable Intermittent or bad connection Check that P1 is properly
connected to J1 (refer to figure
3-1)
Drive belt slipping Replace drive mechanism
Defective component in Troubleshoot and replace
tachometer feedback circuit (U5, defective component (see
VR2, Q6) waveforms, p. 4-10)
Drive motor bearings Replace drive motor

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Field Service Manual 31
 SYMPTOM CHECKLIST (Continued)

STEPPER MOTOR PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Head positioner will not step Bad connection at J15 Check for proper connection and
polarity at J15 (refer to figure 3-
1)
Defective component in stepper Troubleshoot and replace
driver circuit defective component (see
(U2, U3, U7) waveforms, p. 4-10)
Defective stepper motor Replace drive mechanism
Skips or missteps to wrong Bad connection at J15 Check for proper connection and
tracks polarity at J15 (refer to figure 3-
1)
Defective component in stepper Troubleshoot and replace
driver circuit defective component (see
(U2, U3, U7) waveforms, p. 4-10)
Band pully or head carriage Replace drive mechanism
binding
Track 00 sensor defective need Troubleshoot and replace or
adjustment Q5 adjust defective component (see
waveforms, p. 4-10)

DRIVE MECHANISM PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Diskette will not eject Eject assembly binding or Replace drive mechanism
broken
Drive will not pass track 00 Track 00 sensor defective or Troubleshoot and replace or
sensor test needs adjustment adjust defective component
Carriage stop missing or Replace drive mechanism
improperly set
Defective component in track 00 Troubleshoot and replace
sensor circuit defective component (see
waveforms, p. 4-11)
Intermittent Read/Write errors Head load pad pressure Replace drive mechanism
Dirty Read/Write head Clean head with 91% Isopropyl
Alcohol
Burned head Replace drive mechanism
Diskette incompatibility Radial track alignment Adjust “Cat’s Eyes” alignment
Head azimuth alignment Check head azimuth. If out of
spec., replace drive mechanism
Drive belt slipping Replace drive mechanism
Speed improperly adjusted (VR2) Check and adjust for proper
speed on both drives

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Field Service Manual 32
 SYMPTOM CHECKLIST (Continued)

READ PROBLEMS
SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Soft Read errors (intermittent or Defective Diskette Try diskette on known-good
non-permanent) drive
Dirty Read/Write head Clean head with 91% Isopropyl
Alcohol
Drive belt slipping Replace drive mechanism
Excessive noise in Read signal Troubleshoot Read circuit (see
(U13, U18-20, U22-24) waveforms, p.4-12)
Intermittent or marginal Troubleshoot Read circuit (see
component I Read circuit (U13, waveforms, p.4-12)
U18-20, U22-24)
Fails to read anything Improper connection of J6 Check for correct polarity (refer
to Figure 3-1)
Failed component in read circuit Troubleshoot and replace failed
(U13, U18-20, component (see waveforms, p. 4-
U22-24) 12)
Burned head Replace drive mechanism
Speed adjustment incorrect Adjust speed POT (VR2) for
speed of 208.3 ms
Head load pad pressure Replace drive mechanism
Dirty Read/Write head Clean head with 91% Isopropyl
Alcohol
Radial track alignment Adjust “Cat’s Eyes” alignment
Head azimuth alignment Check head azimuth. If out of
spec., replace drive mechanism

POWER SUPPLY PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
No power or blows power Defective bridge diodes Replace all four diodes (CR17-
CR20) (see waveforms, p. 4-16)
Defective power adaptor Replace power adaptor
No +5V at TP13 Defective 5V regulator Replace Q7
Power LED not lit Defective 5V regulator Replace Q7
Defective LED Replace CR21
No +12V at TP14 Defective 12V regulator Replace Q8
Defective12V doubler circuit Replace CR15 and CR16, or C71
(see waveforms, p.4-16)

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Field Service Manual 33
 SYMPTOM CHECKLIST (Continued)

WRITE PROBLEMS
SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Fails to Write anything Improper connection of J6 Check for correct polarity (refer
to Figure 3-1)
Dirty Read/Write head Clean head with 91% Isopropyl
Alcohol
Defective Write protect circuit Troubleshoot and replace
(U11, U13) defective component (see
waveforms, p. 4-13)
Component failure in Write Troubleshoot and replace
circuit (U13, U15-18, U21, Q1) defective component (see
waveforms, p. 4-14)
Defective component in Erase Troubleshoot and replace
circuit (U11, U15, U17) defective component (see
waveforms, p. 4-15)
Burned head Replace drive mechanism
Error 144 during Write or format Defective Write protect circuit Troubleshoot and replace
routine (U11, U13) defective component (see
waveforms, p. 4-13)
Writes garbled data Defective component in Erase Troubleshoot and replace
circuit (U11, U15, U17) defective component (see
waveforms, p. 4-15)
Component failure in Write Troubleshoot and replace
circuit (U13, U15-18, U21, Q1) defective component (see
waveforms, p. 4-14)
Dirty Read/Write head Clean head with 91% Isopropyl
Alcohol
Drive is always or never Write Defective Write protect circuit Troubleshoot and replace
protected (U11, U13) defective component (see
waveforms, p. 4-13)
Defective Write protect photo Replace drive mechanism
sensor

DRIVE SELECT PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Drive select test fails Defective select switch Replace S2
Defective PIA Replace U7

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Field Service Manual 34
 SYMPTOM CHECKLIST (Continued)

DATA INTERFACE PROBLEMS

SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
No response to commands from I/O cable connections Replace cable or tighten
computer connections
Command signal not getting to Trace signal through (U1) and
PIA (U7) replace if necessary (see
waveforms, p. 4-17 )
Defective PIA Replace U7
No data output from drive to I/O cable connections Replace cable or tighten
computer connections
Data signal from PIA not getting Trace signal through (U1) and
to I/O connection replace if necessary (see
waveforms, p. 4-17 )
Defective PIA Replace U7
No data input from computer to I/O cable connections Replace cable or tighten
drive connections
Data signal not getting to PIA Trace signal through (U1) and
(U7) replace if necessary (see
waveforms, p. 4-17 )
Defective PIA Replace U7
Drive doesn’t reboot when VCC Ready signal not getting to Trace signal through (U1) and
computer is powered down and PIA replace if necessary (see
then up again waveforms, p. 4-17 )
Defective PIA Replace U7

If the other circuits have been checked and found good, one of the IC’s in the CPU circuits is defective.

CENTRAL PROCESSING UNIT PROBLEMS

TYPE OF FAILURE POSSIBLE CAUSES
Power-Up failures PIA (U7)
Boot Errors 2793, FDC (U13)
Stepper Motor failures Microprocessor, 6507 (U9)
Drive Motor failures Custom ROM (U10)
I/O failures RAM, 6810 (U8)
Drive code switch not 74LS04, Inverter (U16)
recognized 4MHz Crystal (Y1)
74LS74, D-type, edge-triggered flip-flop (U1)
555, Timer (U4)
74LS00, Nand gate (U6, U12)

NOTE: There is no relationship between the order of failures and possible causes.

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Field Service Manual 35
 SECTION 6
WAVEFORMS

MOTOR CONTROL SIGNALS

Pin 11 of U7

Base of Q4

Collector of Q4

Emitter of Q4

Pin 1 at J12

The collector of Q6 is a constant 12V.

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Field Service Manual 36
 TACH FEEDBACK SIGNALS/SPEED ADJUST

Pin 11 of U7
Schematics, Page 5-7

Pin 5 of U5
Schematics, Page 5-7

Pin 9 of U5 is a Constant 8volts.

When speed pot VR2 is adjusted, the voltage on Pin 10 of U5 increases or decreases. This causes a
corresponding increase or decrease in the frequency of the AC signal on the motor control lines, Pin 8 of
U5 and Pins 11 and 5 of U5.

STEPPER DRIVE SIGNALS

NS01

NS02

NS03

NS04

Pin 3 of U2

Pin 6 of U2

Pin 3 of U3

Pin 6 of U3
Pin 5 of U2 and U3 is +12V DC.

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Field Service Manual 37
 DISKETTE ENABLE SIGNAL

Enabled Disabled

(IC U6) (IC U6)

Pin 10 = 0V Pin 10 = 5V
Pin 12 = 5V Pin 12 = 0V
Pin 8 = 4.5V Pin 8 = 4.5V

TRACK 00 SIGNAL

Base of Q5
Schematics, Page 5-7

Collector of Q5
Schematics, Page 5-7

DATA - IN SIGNAL

Pin 2 of U1

Pin 1 of U1

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Field Service Manual 38
 READ SIGNALS

TP1 or TP2

TP3 or TP4

TP5

TP16

TP6

Pin 27 of U13

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Field Service Manual 39
 WRITE SIGNALS

TP11

Pin 9 of U18

Pin 8 of U11

Pin 5 of U21

Pin 1 of U21

WRITE GATE SIGNALS

Pin 10 of U16

Pin 9 of U21

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Field Service Manual 40
 ERASE GATE SIGNAL

Pin 10 of U16

Pin 5 of U15

Pin 13 of U15

Pin 8 of U21

Collector of Q1

ERASE SIGNAL

Pin 1 of U11

Pin 10 or 12 of U17

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Field Service Manual 41
 CLOCK SIGNALS

Pin 13 of U16
4MHz Clock

Pin 5 of U14
1MHz Clock

Pin 6 of U6
Phase 0 Clock

WRITE PROTECT SIGNAL

Pin 11 of U11

Pin 13 of U11

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Field Service Manual 42
 POWER SUPPLY SIGNALS (AC)

Cathode of CR20

Cathode of CR20

Cathode of CR20

Cathode of CR20

Cathode of CR20

Anode of CR21 = 1.7V DC

TP13 = +5V DC
TP14 = +12V DC
TP15 = GND

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Field Service Manual 43
 DATA OUT SIGNAL

Pin 9 of U1

Pin 14 of U1

COMMAND SIGNAL

Pin 4 of U1

Pin 5 of U1

VCC/READY SIGNAL

Pin 6 of U1

Pin 8 of U1

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Field Service Manual 44
 SECTION 7
SCHEMATICS AND SILKSCREENS

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Field Service Manual 45
1050 Disk Drive
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1050 Disk Drive
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1050 Disk Drive
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1050 Disk Drive
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1050 Disk Drive
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 SECTION 8
1050 PARTS LIST
(TANDON)

PART
LOCATOR DESCRIPTION NUMBER
TM 50-1 Drive Mechanism (TANDON) FA100514
Enclosure, Top FC100515
Enclosure, Bottom FC100516
Front Bezel FC100517
Photo Sensor FC100518
Ready Switch Assembly FA100519
Spindle Motor FC100520
1050 PCB Assembly FA100513
L3 Inductor, 270µH FC100521
L1, 2 Inductor, 390µH FC100522
R2 Resistor, 150Ω, 2W FC100524
VR2 Potentiometer, Cermet, 2kΩ FC100525
VR3,5 Potentiometer, Cermet, 25kΩ FC100526
Q2, 4, 5 Transistor, 2N4124 FC100527
Q1, 3 Transistor, 2N4403 FC100528
Q6 Transistor, TIP110 FC100529
CR1-7, 10, 12, 13 Diode, 1N4446 ( 75V/100mA switching) FC100530
CR11 Zener diode 1N5224B, 6V2 FC100531
CR9 Zener diode 1N5226B, 3V3 FC100532
CR8 Zener diode 1N5230B, 4V7 FC100533
Y1 Crystal, 4MHz FC100534
U15 74LS123, I.C. FC100535
U5 LM2917, I.C. CO17101
U2, 3 SN75478, I.C. (5713) FC100536
C36 Capacitor Variable 12-70pF FC100543
U22 LM733, I.C. FC100537
U23 NE592, I.C. CO17951
U24 LM311, I.C. CO14332
U17 SN7406, I.C. FC100538
U19 74LS86, I.C. 37-74LS86
U20 74LS221, I.C. FC100540
U14, 18 74LS74, I.C. CO16045
U1, 21 LM3086, I.C. (CA3086) CO16821
U6, 12 74LS00, I.C. CO14341
U11 74LS02, I.C. CO14340
U16 74LS04, I.C. CO17096
U4 LM555, I.C. CO19748
U10 ROM, Custom 2732, I.C. FC100541
U8 RAM, 6819 (1MHz), I.C. CO14328
U9 MPU, 6507 (1MHz), I.C. CO10745
U13 FDC, WD2793-02, I.C. FC100542
U7 PIA, 6532 (RIOT), I.C. CO10750
CR17, 18, 19, 20 Diode, MR501 CO14398

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