Keithley 2001 Service Manual

Model 2001

Multimeter

Repair Manual

Contains Servicing Information

W ARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 3 years from date
of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries,
diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithle y representative, or contact Keithle y headquarters in Cleveland, Ohio. Y ou will
be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility. Repairs
will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance of the origi­nal warranty period, or at least 90 days.

LIMIT A TION OF W ARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or misuse of
any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leakage, or
problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE
BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDI­RECT , SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND
SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF
SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL
AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.

Keithley Instruments, Inc. • 28775 Aurora Road • Cleveland, OH 44139 • 216-248-0400 • Fax: [phone] • http://www.keithley.com
CHINA: Keithley Instruments China • Yuan Chen Xin Building, Room 705 • No. 12 Yumin Road, Dewei, Madian • Beijing, China 100029 • 8610-2022886 • Fax: [phone]

FRANCE: Keithley Instruments SARL • BP 60 • 3 allée des Garays • 91122 Palaiseau Cédex • 31-6-0115155 • Fax: [phone]
GERMANY: Keithley Instruments GmbH • Landsberger Straße 65 • 82110 Germering • 49-89-849307-0 • Fax: [phone]
GREAT BRITAIN: Keithley Instruments, Ltd. • The Minster • 58 Portman Road • Reading, Berkshire RG30 1EA • 44-01734-575666 • Fax: [phone]
ITALY: Keithley Instruments SRL • Viale S. Gimignano 38 • 20146 Milano • 39-2-48303008 • Fax: [phone]
JAPAN: Keithley Instruments Far East KK • Aibido Bldg. • 7-20-2 Nishishinjuku • Shinjuku-ku, Tokyo 160 • 81-3-5389-1964 • Fax: [phone]
NETHERLANDS: Keithley Instruments BV • Avelingen West 49 • 4202 MS Gorinchem • 31-(0)183-635333 • Fax: [phone]
SWITZERLAND: Keithley Instruments SA • Kriesbachstrasse 4 • 8600 Dübendorf • 41-1-8219444 • Fax: [phone]
TAIWAN: Keithley Instruments Taiwan • 1, Ming-Yu First Street • Hsinchu, Taiwan, R.O.C. • 886-35-778462 • Fax: [phone]

Model 2001 Multimeter

Repair Manual

©1993, Keithley Instruments, Inc.

Test Instrumentation Group

All rights reserved.

Cleveland, Ohio, U.S.A.

Second Printing, February 1996

Document Number: 2001-902-01 Rev. B

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created for this manual. The
Revision Level letter increases alphabetically as the manual undergoes subsequent updates. Addenda, which are
released between Revisions, contain important change information that the user should incorporate immediately
into the manual. Addenda are numbered sequentially. When a new Revision is created, all Addenda associated
with the previous Revision of the manual are incorporated into the new Revision of the manual. Each new Revi­sion includes a revised copy of this print history page.

Revision A (Document Number 2001-902-01).................................................................................. April 1993

Revision B (Document Number 2001-902-01)........................................................................... February 1996

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.

Other brand and product names are trademarks or registered trademarks of their respective holders.

Safety Precautions

The following safety precautions should be observed before
using this product and any associated instrumentation. Al­though some instruments and accessories would normally be
used with non-hazardous voltages, there are situations
where hazardous conditions may be present.

This product is intended for use by qualiÞed personnel who
recognize shock hazards and are familiar with the safety pre­cautions required to avoid possible injury. Read the operat­ing information carefully before using the product.

Exercise extreme caution when a shock hazard is present. Le­thal voltage may be present on cable connector jacks or test
Þxtures. The American National Standards Institute (ANSI)
states that a shock hazard exists when voltage levels greater
than 30V RMS, 42.4V peak, or 60VDC are present.

safety practice is to expect that hazardous voltage is present
in any unknown circuit before measuring.

Before operating an instrument, make sure the line cord is
connected to a properly grounded power receptacle. Inspect
the connecting cables, test leads, and jumpers for possible
wear, cracks, or breaks before each use.

For maximum safety, do not touch the product, test cables, or
any other instruments while power is applied to the circuit
under test. ALWAYS remove power from the entire test sys­tem and discharge any capacitors before: connecting or dis­connecting cables or jumpers, installing or removing
switching cards, or making internal changes, such as install­ing or removing jumpers.

Do not touch any object that could provide a current path to
the common side of the circuit under test or power line
(earth) ground. Always make measurements with dry hands
while standing on a dry, insulated surface capable of with­standing the voltage being measured.

A good

Do not exceed the maximum signal levels of the instruments
and accessories, as deÞned in the speciÞcations and operat­ing information, and as shown on the instrument or test Þx­ture rear panel, or switching card.

Do not connect switching cards directly to unlimited power
circuits. They are intended to be used with impedance limit­ed sources. NEVER connect switching cards directly to AC
main. When connecting sources to switching cards, install
protective devices to limit fault current and voltage to the
card.

When fuses are used in a product, replace with same type
and rating for continued protection against Þre hazard.

Chassis connections must only be used as shield connections
for measuring circuits, NOT as safety earth ground connec­tions.

If you are using a test Þxture, keep the lid closed while power
is applied to the device under test. Safe operation requires the
use of a lid interlock.

If a screw is present on the test Þxture, connect it to safety
earth ground using #18 AWG or larger wire.

The symbol on an instrument or accessory indicates that
1000V or more may be present on the terminals. Refer to the
product manual for detailed operating information.

Instrumentation and accessories should not be connected to
humans.

Maintenance should be performed by qualiÞed service per­sonnel. Before performing any maintenance, disconnect the
line cord and all test cables.

Table of Contents

1 Routine Maintenance

1.1 Introduction.......................................................................................................................................................1-1

1.2 Line fuse replacement.......................................................................................................................................1-1

1.3 Current fuse replacement ..................................................................................................................................1-2

1.3.1 Front AMPS input fuse............................................................................................................................ 1-2

1.3.2 Rear AMPS input fuse.............................................................................................................................1-2

1.4 Fan filter cleaning .............................................................................................................................................1-3

1.5 Firmware updates..............................................................................................................................................1-3

2 T roubleshooting

2.1 Introduction.......................................................................................................................................................2-1

2.2 Repair considerations........................................................................................................................................2-1

2.3 Power-on test.....................................................................................................................................................2-2

2.4 Front panel tests ................................................................................................................................................2-2

2.4.1 KEYS Test...............................................................................................................................................2-2

2.4.2 DISPLAY PATTERNS Test................................................................................................................... 2-3

2.5 Built-in test........................................................................................................................................................2-3

2.5.1AUTOMATIC Testing2-6

2.5.2 MANUAL Testing...................................................................................................................................2-6

2.6 Diagnostics........................................................................................................................................................2-7

2.7 R1_STB and R2_STB shift registers ..............................................................................................................2-11

2.8 Display board checks ......................................................................................................................................2-14

2.9 Power supply checks.......................................................................................................................................2-14

2.10 Documentation................................................................................................................................................2-15

2.10.1 Display board circuit theory.................................................................................................................. 2-17

2.10.2 Power supply circuit theory...................................................................................................................2-17

2.10.3 Built-in test documentation ...................................................................................................................2-18

3 Disassembly

3.1 Introduction.......................................................................................................................................................3-1

3.2 Handling and cleaning precautions...................................................................................................................3-1

3.2.1 PC-board handling...................................................................................................................................3-1

i

3.2.2 Solder repairs........................................................................................................................................... 3-2

3.3 Special handling of static sensitive devices......................................................................................................3-2

3.4 Case cover and shield removal ......................................................................................................................... 3-2

3.4.1 Case cover removal................................................................................................................................. 3-2

3.4.2 Analog board top shield removal ............................................................................................................ 3-3

3.5 PC-boards removal ........................................................................................................................................... 3-3

3.5.1 Digital board............................................................................................................................................ 3-3

3.5.2 A/D converter board................................................................................................................................3-3

3.5.3 Analog board........................................................................................................................................... 3-4

3.6 Front panel disassembly.................................................................................................................................... 3-5

3.7 Cooling fan removal ......................................................................................................................................... 3-5

3.8 Main CPU firmware replacement..................................................................................................................... 3-6

3.9 Instrument re-assembly.....................................................................................................................................3-6

3.10 Assembly drawings...........................................................................................................................................3-6

4 Replaceable Parts

4.1 Introduction....................................................................................................................................................... 4-1

4.2 Parts lists........................................................................................................................................................... 4-1

4.3 Ordering information........................................................................................................................................ 4-1

4.4 Factory service..................................................................................................................................................4-1

4.5 Component layouts........................................................................................................................................... 4-1

ii

List of Illustrations

1 Routine Maintenance

Figure 1-1 Line fuse location ................................................................................................................................. 1-1

Figure 1-2 Front AMPS input fuse location........................................................................................................... 1-2

Figure 1-3 Rear AMPS input fuse location............................................................................................................ 1-3

2 T roubleshooting

Figure 2-1 Model 2001 overall block diagram..................................................................................................... 2-16

iii

Ω

Ω

Ω

List of Tables

1 Routine Maintenance

Table 1-1 Power line fuse ..................................................................................................................................... 1-2

Table 1-2 Current fuse .......................................................................................................................................... 1-2

2 T roubleshooting

Table 2-1 Built-in-test summary........................................................................................................................... 2-3

Table 2-2 DIAGNOSTICS test modes (all functions except
Table 2-3 DIAGNOSTICS test modes (
Table 2-4 DIAGNOSTICS test modes (

Table 2-5 DIAGNOSTICS bit patterns (DC_STB registers).............................................................................. 2-10

Table 2-6 Bit patterns for R1_STB registers....................................................................................................... 2-12

Table 2-7 Bit patterns for R2_STB registers....................................................................................................... 2-13

Table 2-8 Display board checks.......................................................................................................................... 2-14

Table 2-9 Power supply checks........................................................................................................................... 2-15

Table 2-10 DC_STB control registers................................................................................................................... 2-19

Table 2-11 R1_STB control registers ................................................................................................................... 2-20

Table 2-12 R2_STB control registers ................................................................................................................... 2-21

Table 2-13 Multiplexer (U511)............................................................................................................................. 2-22

4 function; 20 Ω and 200 Ω ranges)..................................................... 2-9

4 function; 2k Ω thru 200k Ω ranges) .................................................. 2-9

4)......................................................................... 2-8

4 Replaceable Parts

Table 4-1 Model 2001 A/D board, parts list......................................................................................................... 4-2

Table 4-2 Model 2001 analog board, parts list ..................................................................................................... 4-5

Table 4-3 Model 2001 digital board, parts list.................................................................................................... 4-15

Table 4-4 Model 2001 display board, parts list................................................................................................... 4-19

Table 4-5 Model 2001 miscellaneous, parts list...................................................................................................4-21

v

OR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.

OR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.

AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.

1

Routine Maintenance

1.1 Introduction

In general, the information in this section deals with
routine type maintenance that can be performed by the
operator. This information is arranged as follows:

1.2 Line fuse replacement

place a blown line power fuse.

1.3 Current fuse replacement

place a blown current fuse.

1.4 Fan Þlter cleaning

and clean the Þlter element for the cooling fan.

1.5 Firmware updates

action for Þrmware updates provided by Kei­thley.



Explains how to re-



Explains how to re-



Explains how to remove



Recommends a course of

1.2 Line fuse replacement

WARNING

Disconnect the line cord at the rear
panel. Remove all test leads connect­ed to the instrument (front and rear).

1. Insert a bladed screwdriver into the slot of the fuse
carrier.

2. While pushing in, turn the screwdriver counter­clockwise until the spring loaded fuse carrier re­leases from the fuse holder.

3. Pull out the fuse carrier and replace the fuse with
the type speciÞed in Table 1-1.

CAUTION

To prevent instrument damage, use
only the fuse type speciÞed in Table
1-1.

4. Re-install the fuse carrier.

DIGITAL I/O

IN OUT

TRIGGER

LINK

LINE RATING

90-134VAC

180-250VAC

50, 60, 400HZ

55VA MAX

(CHANGE IEEE ADDRESS

WITH FRONT PANEL MENU)

IEEE-488

LINE FUSE

SLOWBLOW

1/2A, 250V

Line

Fuse

The power line fuse is accessible from the rear panel,
just below the ac power receptacle (see Figure 1-1). Per­form the following steps to replace the line fuse:

Figure 1-1

Line fuse location

1-1

Routine Maintenance

NOTE

If the power line fuse continues to
blow, a circuit malfunction exists and
must be corrected. Refer to the trou­bleshooting section of this manual for
assistance.

Table 1-1

Power line fuse

Keithley

Size Rating

5

×

20mm 250V, ½ A, Slo-Blo FU-71

Part No.

1.3 Current fuse replacement

Each AMPS input (front and rear) has its own current
fuse. When replacing a current fuse, use the type spec­iÞed in Table 1-2.

CAUTION

To prevent instrument damage, use
only the type speciÞed in Table 1-2.

3. Re-install the fuse carrier.

SENSE

MATH 4W AUTO ARM TRIG SMPL

2001 MULTIMETER

RANGE

AUTO

RANGE

Ω 4 WIRE

350V
PEAK

INPUTS

FR

FRONT/REAR

INPUT

HI

1100V

!

PEAK

LO

500V
PEAK

2A 250V

AMPS

CAL

AMPS

Fuse

Table 1-2

Current fuse

Keithley

Size Rating

5

×

20mm 250V, 2A, Normal-Blo FU-48

Part No.

WARNING

Disconnect the instrument from the
power line and remove all test leads
(front and rear).

1.3.1 Front AMPS input fuse

The front panel AMPS jack functions as the AMPS in­put terminal and as the carrier for the AMPS fuse (see
Figure 1-2). Perform the following steps to replace the
fuse:

Figure 1-2

Front AMPS input fuse location

1.3.2 Rear AMPS input fuse

The rear AMPS input fuse is located just below the
AMPS input jack (see Figure 1-3). Perform the follow­ing steps to replace the fuse:

1. Insert a bladed screwdriver into the slot of the fuse
carrier.

2. While pushing in, turn the screwdriver counter­clockwise until the spring loaded fuse carrier re­leases from the fuse holder.

3. Pull out the fuse carrier and replace the fuse with
the type speciÞed in Table 1-2.

CAUTION

1. Push in the AMPS input jack and turn counter­clockwise until the spring loaded fuse carrier re­leases from the fuse holder.

2. Pull out the fuse carrier and replace the fuse with
the type speciÞed in Table 1-2.

1-2

To prevent instrument damage, use
only the fuse type speciÞed in Table
1-2.

4. Re-install the fuse carrier.

WARNING:NO INTERNAL OPERATOR SERVICABLE PARTS,SERVIC

WARNING:NO INTERNAL OPERATOR SERVICABLE PARTS,SERVIC

CAUTION:FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLA

CAUTION:FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLA

INPUT

1100V

!

HI LO

PEAK

350V

PEAK

SENSE

Ω 4 WIRE

OPTION SLOT

Figure 1-3

Rear AMPS input fuse location

500V
PEAK

AMPS

2A MAX

AMPS
FUSE

2A, 250V

Amps

Fuse

EXTERNAL

TRIGGER

INPUT

Routine Maintenance

the cover plate.

WARNING

Exercise care when handling the Þl­ter assembly. The Þlter element is a
metal screen with sharp edges that
could cause injury if not handled
carefully.

The Þlter element is made of a rugged metal screen al­lowing the use of any type cleaning solution to clean it.
A small metal brush can be used to remove dirt and de­bris. After cleaning the Þlter, rinse thoroughly with wa­ter. Make sure the Þlter assembly is completely dry
before re-installing it.

1.4 Fan filter cleaning

The Þlter for the cooling fan requires periodic cleaning
to maintain proper ventilation. The fan Þlter is accessi­ble from the rear panel. Perform the following steps to
remove the Þlter for cleaning:

1. While facing the rear panel, locate the lower right­hand corner of the Þlter cover plate.

2. At this corner, place a thin-bladed screwdriver be­tween the cover plate and the rear panel and gently
pry the Þlter assembly away from the chassis.

The Þlter element is permanently Þxed to the cover
plate. Do not attempt to remove the Þlter element from

1.5 Firmware updates

It is possible that you may receive a Þrmware update
from Keithley to enhance operation and/or Þx ÒbugsÓ.
The Þrmware program for the main microprocessor is
contained in U611 (EPROM). A socket is used on the pc
board for this device to make replacement relatively
easy.

The replacement procedure requires that the case cover
be removed. Also, this surface mount, static-sensitive
device requires special handling. As a result, the Þrm­ware update should only be performed by qualiÞed

1-3

Routine Maintenance

service personnel. The procedure to replace the Þrm­ware (U611) is contained in paragraph 3.8.

1-4

2

Troubleshooting

WARNING

The information in this section is in­tended for qualiÞed service person­nel. Some of these procedures may
expose you to hazardous voltages. Do
not perform these hazardous proce­dures unless you are qualiÞed to do
so.

2.1 Introduction

This section of the manual will assist you in trouble­shooting the Model 2001. Included are self-tests, test
procedures, troubleshooting tables and circuit descrip­tions. It is left to the discretion of the repair technician
to select the appropriate tests and documentation
needed to troubleshoot the instrument.

This section is arranged as follows:

2.2 Repair considerations

ations that should be noted before making any re­pairs to the Model 2001.

2.3 Power-on test Ñ Describes the tests that are per-

formed on its memory elements every time the
instrument is turned on.



Covers some consider-

2.5 Built-In tests Ñ Provides the procedures to test

and exercise the various circuits on the digital
board, analog board and A/D converter boards.

2.6 Diagnostics Ñ Explains how to use the Diagnos-

tics test mode of the Model 2001. In general, Di­agnostics locks-up the instrument in various
states of operation. With the instrument in a static
state, you can then check the state of the various
logic levels on the control registers and signal
trace through the unit.

2.7 R1_STB and R2_STB registers Ñ Provides shift

register bit patterns for the basic measurement
functions and ranges.

2.8 Display board checks Ñ Provides display board

checks that can be made if Front Panel Tests fail.

2.9 Power supply checks Ñ Provides power supply

checks that can be made if the integrity of the
power supply is questioned.

2.10 Documentation Ñ Provides support documen-

tation for the various troubleshooting tests and
procedures. Included is some basic circuit theory
for the display board and power supply, and sup­port documentation for Built-in Test.

2.4 Front panel tests Ñ Provides the procedures to

test the functionality of the front panel keys and
the display.

2.2 Repair considerations

Before making any repairs to the Model 2001, be sure to
read the following considerations.

2-1

Troubleshooting

CAUTION

The PC-boards are built using sur­face mount techniques and require
specialized equipment and skills for
repair. If you are not equipped and/or
qualiÞed, it is strongly recommend­ed that you send the unit back to the
factory for repairs or limit repairs to
the pc-board replacement level (see
following NOTE).

Without proper equipment and train­ing, you could damage a PC-board
beyond repair.

NOTE

For units that are out of warranty,
completely assembled PC-boards can
be ordered from Keithley to facilitate
repairs.

1. Repairs will require various degrees of disassem­bly. However, it is recommended that the Front
Panel Tests (paragraph 2.4) and Built-In-Test (para­graph 2-5) be performed prior to any disassembly.
The disassembly instructions for the Model 2001
are contained in Section 3 of this manual.

2. Do not make repairs to surface mount pc-boards
unless equipped and qualiÞed to do so (see previ­ous CAUTION).

3. When working inside the unit and replacing parts,
be sure to adhere to the handling precautions and
cleaning procedures explained in paragraph 3.2.

4. Many CMOS devices are installed in the Model

2001. These static-sensitive devices require special
handling as explained in paragraph 3.3.

5. Anytime a circuit board is removed or a compo­nent is replaced, the Model 2001 will have to be
recalibrated.

2.4 Front panel tests

There are two Front Panel Tests; one to test the func­tionality of the front panel keys and one to test the dis­play. In the event of a test failure, refer to paragraph 2.8
to troubleshoot the display board.

2.4.1 KEYS Test

The KEYS test allows you to check the functionality of
each front panel key. Perform the following steps to
run the KEYS test.

1. Display the MAIN MENU by pressing the MENU
key.

2. Use the or key to place the cursor on TEST
and press ENTER to display the SELF-TEST
MENU.

3. Place the cursor on FRONT-PANEL-TESTS and
press ENTER to display the following menu:

FRONT PANEL TESTS

KEYS DISPLAY-PATTERNS

4. Place the cursor on KEYS and press ENTER to start
the test. When a key is pressed, the label name for
that key will be displayed to indicate that it is func­tioning properly. When the key is released, the
message ÒNo keys pressedÓ is displayed.

5. Pressing EXIT tests the EXIT key. However, the sec­ond consecutive press of EXIT aborts the test and
returns the instrument to the SELF-TEST MENU.
Keep pressing EXIT to back out of the menu struc­ture.

2.4.2 DISPLAY PATTERNS Test

The display test allows you to verify that each pixel
and annunciator in the vacuum ßuorescent display is
working properly. Perform the following steps to run
the display test:

2.3 Power-on test

During the power-on sequence, the Model 2001 will
perform a checksum test on its EPROM (U611 and
U618) and test its RAM (U608, U609, and U610. If one
of these tests fail the instrument will lock up.

2-2

1. Display the MAIN MENU by pressing the MENU
key.

2. Use the or key to place the cursor on TEST
and press ENTER to display the SELF-TEST
MENU.

3. Place the cursor on FRONT-PANEL-TESTS and
press ENTER to display the following menu:

Troubleshooting

FRONT PANEL TESTS

KEYS DISPLAY-PATTERNS

4. Place the cursor on DISPLAY-PATTERNS and
press ENTER to start the display test. There are Þve
parts to the display test. Each time a front panel
key (except EXIT) is pressed, the next part of the
test sequence is selected. The Þve parts of the test
sequence are as follows:

A. Checkerboard pattern (alternate pixels on) and

all annunciators.

B. Checkerboard pattern and the annunciators

that are on during normal operation.

C. Horizontal lines (pixels) of the Þrst digit are se-

quenced.

D. Vertical lines (pixels) of the Þrst digit are se-

quenced.

E. Each digit (and adjacent annunciator) is se-

quenced. All the pixels of the selected digit are
on.

5. When Þnished, abort the display test by pressing
EXIT. The instrument returns to the SELF-TEST
MENU. Keep pressing EXIT to back out of the
menu structure.

Table 2-1

Built-in-test summary

Test Circuit tested/exercised

100 Series

100.1

101 Series

101.1

102 Series

102.1

103 Series

103.1 - 103.4

103.5

104 Series

104.1

104.2

105 Series

105.1 - 105.6

105.7

Memory:

EPROM

Memory:

RAM

Memory:

2

E

PROM

Digital I/O:

Digital Output
Digital Input

IEEE-488 Bus:

Handshake
Data

Triggers:

System Trigger Bus
External Trigger /Voltme­ter Complete

105.8

Group Execute Trigger
(GET)

105.11 - 105.18

Trigger Shorts

2.5 Built-in test

BUILT-IN TEST is used to test and exercise various cir­cuits and components on the digital board, analog
board and A/D converter board. The Built-In Tests are
listed in Table 2-1. Many of the tests are actual pass/fail
type tests, while others are circuit exercises that are
used for subsequent tests. Each Built-In Test can be run
manually. After a test is manually run, operation is
ÒfrozenÓ to allow the technician to troubleshoot the cir­cuit. Troubleshooting documentation for each Built-In
Test is provided in paragraph 2.10.3.

200 Series

200.1

200.2

200.3

200.4

200.5

200.6

200.7

201 Series

201.1

201.2

201.3

300 Series

300.1

300.2

300.3

301 Series

301.1

301.2

A/D Converter:

A/D Zero
A/D Noise
FAST Circuit
x10 Line Cycle Integration
x0.1 Line Cycle Integration
x0.02 Line Cycle Integra­tion
x0.01 Line Cycle Integra­tion

Calibration:

Test Cal Zero
7V Reference

1.75V Reference

A/D Multiplexer (MUX),
A/D Buffer:

7V Reference, x1.5 Gain

1.75V Reference, x5 Gain
0V Reference, x50 Gain

Input Buffer:

Front End (FE) Zero
Divide by 100

2-3

Troubleshooting

Table 2-1 (cont.)

Built-in-test summary

Test Circuit tested/exercised

302 Series

302.1

Ohms:

Zero Reference Measure­ment (for next test)

302.2

Open Circuit Ohms and
Ohms Protection

303 Series

303.1

Input Path:

Zero Reference Measure­ment (for next test)

303.2

Open Circuit Ohms and
Ohms Protection

303.3

Front End (FE) Zero Pro­tection

304 Series

304.1

Ohms Sources:

Zero Reference Measure­ment (for tests 304.2 -

304.7)

304.2

0.98mA and 9.2mA Ohms
Sources

304.3

89

µ

A and 0.98mA Ohms

Sources

304.4

7

µ

A and 89

µ

A Ohms

Sources

304.5

770nA and 7

µ

A Ohms

Sources

304.6

70nA and 770nA Ohms
Sources

304.7

4.4nA and 770nA Ohms
Sources

Table 2-1 (cont.)

Built-in-test summary

Test Circuit tested/exercised

308 Series

308.1

4-Digit Mode:

A/D MUX 4-Digit Signal
Path

308.2

A/D MUX 4-Digit Zero
Path

309 Series

309.1

309.2

309.3

309.4

Amps:

A Range

200

µ

2mA Range
20mA Range
Reference Measurement
(for tests 309.5 and 309.6)

309.5

309.6

310 Series

310.1

400 Series

200mA Range
2A Range

Protection:

Amps Protection

Digital-to-Analog Converter
(DAC):

400.1

400.2

400.3

400.4

400.5

401 Series

401.1

402 Series

402.1

-4.21V Output

-2.08V Output

-0.001V Output
+2.25V Output
+4.33V Output

Signal Switching:

Zero Cal Switch

Signal Switching:

Frequency Switch

305 Series

305.1

305.2

306 Series

306.1

307 Series

307.1

307.2

307.3

2-4

Input Divider:

Zero Reference Measure­ment (for next test)
Divide by 100

Switching:

Ohms Cal Switch

Cal Divider:

Zero Reference Measure­ment (for next test)
A/D MUX /10
A/D MUX /Buffer (x-0.5)

403 Series

403.1

404 Series

404.1

404.2

404.3

404.4

404.5

Signal Switching:

Ground Switch

Absolute Value (x1 Gain):

-Full Scale DAC Output

-Half Scale DAC Output
Zero DAC Output
+Half Scale DAC Output
+Full Scale DAC Output

Troubleshooting

Table 2-1 (cont.)

Built-in-test summary

Test Circuit tested/exercised

405 Series

405.1

405.2

405.3

405.4

405.5

405.6

405.7

405.8

406 Series

406.1

406.2

406.3

406.4

406.5

406.6

407 Series

407.1

407.2

407.3

408 Series

408.1

408.2

408.3

408.4

408.5

408.6

Absolute Value (x10 Gain):

Gain Comparison (Large
+DAC Output)
Gain Comparison (Large
+DAC Output)
Gain Comparison (Small
+DAC Output)
Gain Comparison (Small
+DAC Output)
Gain Comparison (Small

-DAC Output)

Gain Comparison (Small

-DAC Output)

Gain Comparison (Large

-DAC Output)

Gain Comparison (Large

-DAC Output)

Test Buffer:

Measure DAC Output (for
test 406.6)
Test Buffer Output (-1.13V)
Read Test Buffer (for test

406.6)
Read DAC Output (for test

406.6)
Test Buffer Output (-0.01V)
Voltage Comparisons

Front End:

2V Range
200V Range
750V Range

/200 Correction Factor:

Circuit Setup (for next test)
Signal Stored (for next test)
Setup (for test 408.5) and
Measurement (for test

408.6)
Same as Test 408.3 but no
measurement.
Signal Stored (for next test)
Signal Comparisons

Table 2-1 (cont.)

Built-in-test summary

Test Circuit tested/exercised

409 Series

409.1

409.2

409.3

409.4

409.5

409.6

410 Series

410.1

411 Series

411.1

411.2

412 Series

412.1

/750 Correction Factor:

Circuit Setup (for next test)
Signal Stored (for next test)
Setup (for test 409.5) and
Measurement (for test

409.6)
Same as Test 409.3 but no
measurement.
Signal Stored (for next test)
Signal Comparisons

Converter:

TRMS Converter

Filters:

TRMS Filter
Variable Gain AmpliÞer
Filter

Switching:

AC Amps Switch

Typical Way To Use BUILT-IN-TEST

1. Run the AUTOMATIC Built-In-Test as explained in
paragraph 2.5.1 and note the Þrst (lowest num­bered) test that has failed. You should always ad­dress the lowest numbered test failure Þrst because
that failure could cause subsequent tests to fail.

2. Familiarize yourself with the failed circuit. Docu­mentation for the Built-In Tests are provided in
paragraph 2.10.3. Be sure to read the documenta­tion for the complete series. For example, if test

200.4 fails, read the documentation for all 200 se­ries tests (200.1 through 200.7). Note that the docu­mentation directs you to the appropriate
schematic(s) for the circuit.

3. Manually run the test that failed as explained in
paragraph 2.5.2. Keep in mind that many of the
pass/fail type tests require that one or more circuit
exercise tests be run Þrst. Using the manual step
looping mode will ÒfreezeÓ instrument operation
after a test is run.

4. After manually running the test, use the test docu­mentation and your troubleshooting expertise to
locate the problem.

2-5

Troubleshooting

5. After repairing the instrument, start again at step 1
to check the integrity of the repair and to see if
there are any other failures.

2.5.1 AUTOMATIC Testing

1. Display the MAIN MENU by pressing the MENU
key.

2. Use the or key to place the cursor on TEST
and press ENTER to display the SELF-TEST
MENU.

3. Place the cursor on BUILT-IN-TEST and press EN­TER to display the following menu:

BUILT-IN TEST

AUTOMATIC MANUAL

4. Place the cursor on AUTOMATIC and press EN­TER. The following prompt is displayed:

CONTINUOUS REPEAT?

NO YES

The star (*) is only displayed if a failure occurs.

7. If all the tests passed (no star displayed), use the
EXIT key to back out of the menu structure. Other­wise, press ENTER to display the test number of
the Þrst failure. You can display any additional fail­ures by using the and keys. With a failed test
displayed, pressing the INFO key provides an ab­breviated description of the failure. Paragraph 2.10
provides detailed documentation for troubleshoot­ing the defective circuit. When Þnished, use EXIT
to back out of the menu structure.

2.5.2 MANUAL Testing

1. Display the MAIN MENU by pressing the MENU
key.

2. Use the or key to place the cursor on TEST
and press ENTER to display the SELF-TEST
MENU.

3. Place the cursor on BUILT-IN-TEST and press EN­TER to display the following menu:

In the non-repeat mode (NO), the testing process
stops after all tests have been performed one time.
In the continuous repeat mode (YES), the testing
process loops around and repeats indeÞnitely until
the EXIT key is pressed to stop the tests.

5. Place the cursor on the desired repeat mode selec­tion (NO or YES) and press ENTER to start the test­ing process. The instrument displays the number
of the test being run. An ÒAÓ on the display indi­cates that the tests are being run automatically in
the non-repeat mode. An ÒACÓ indicates that the
tests are being run automatically in the continuous
repeat mode. If a failure occurs, a star (*) appears at
the right hand end of the display and remains on
for the remainder of the tests.

6. If the non-repeat mode is selected, the testing pro­cess automatically stops when all the tests have
been performed. If the continuous repeat mode is
selected, you will have to manually stop the testing
process by pressing EXIT. When EXIT is pressed,
all the tests in a series already started will be al­lowed to Þnish.

When the testing process stops, the following mes­sage is displayed:

All tests complete *

Press ENTER to review or EXIT

BUILT-IN TEST

AUTOMATIC MANUAL

4. Place the cursor on MANUAL and press ENTER to
display the currently selected test series number.

Test number: 100

This test number indicates that the 100 series tests
can be performed. In this case there is only one test;
test 100.1.

5. Use the or to display the desired test series
number. For example, if you wish to run test 200.5,
display the series 200 test number.

Test number: 200

6. With the desired test series number displayed,
press ENTER. The following menu displayed:

SELECT LOOPING

SINGLE CONTINUOUS STEP

7. Place the cursor on the desired looping selection
and press ENTER.

A. SINGLE Looping performs all the tests in the

speciÞed series. The instrument displays the
number of the test being run, and an ÒMÓ is dis-

2-6

Troubleshooting

played to indicate that the tests are being run in
the manual single looping mode. If a failure oc­curs, a star (*) appears at the right hand end of
the display and remains on for the remainder
of the tests in the series. This testing process au­tomatically stops after the last test in the series
is completed. This test process can also be
stopped by pressing EXIT. When EXIT is
pressed, any test in process will be allowed to
Þnish before aborting the testing process.

B. CONTINUOUS looping continuously repeats

all the tests in the speciÞed series until the test­ing process is manually stopped. During test­ing, the ÒMCÓ message is displayed to indicate
that tests are being run in the manual continu­ous looping mode. If a failure occurs, a star (*)
appears at the right hand end of the display
and remains on for the remainder of the tests in
the series. This test process can be stopped by
pressing EXIT. When EXIT is pressed, any test
in process will be allowed to Þnish before
aborting the testing process.

C. STEP looping is used to perform one test at a

time. Each press of the ENTER key performs
the displayed test. The ÒMSÓ message is dis­played to indicate that tests are being run in the
manual step looping mode. If a failure occurs,
a star (*) appears at the right hand end of the
display and remains on for the remainder of
the tests in the series. The instrument automat­ically aborts the testing process after the last
test in the series is run. If you do not wish to
run all the tests in the series, simply press EXIT
after the desired test is run.

8. After the testing process is stopped, the following
message is displayed:

All tests complete *

Press ENTER to review or EXIT

The star (*) is only displayed if a failure occurs.

9. In the event of no test failures, press any key to re­turn to the BUILT-IN TEST menu. If you wish to
run more tests, repeat steps 4 through 8.

In the event of a failure, press ENTER to display
the Þrst test that failed. Other test failures can be
displayed by using the and keys. The INFO
key can be used to provide a brief summary of each
displayed test failure. Paragraph 2.10.3 provides
detailed documentation for troubleshooting the
defective circuit. When Þnished, press EXIT to re-

turn to the BUILT-IN TEST menu. If you wish to
run more tests, repeat steps 4 through 8.

10. When Þnished with BUILT-IN TEST, use the EXIT
key to back out of the menu structure.

2.6 Diagnostics

The Model 2001 has diagnostic test modes which allow
you to ÒfreezeÓ instrument operation to allow you to
check logic levels on the DC_STB control registers
(U303, U300, U800 and U801). The known bit pattern at
these registers can then be used for signal tracing
through the unit. Table 2-10 provides a brief descrip­tion of each register bit.

Perform the following steps to use DIAGNOSTICS:

1. Select the desired function and range to be
checked. Note that there are no range selections for
FREQ and TEMP.

2. Display the MAIN MENU by pressing the MENU
key.

3. Using the or key to place the cursor on TEST
and press ENTER to display the SELF-TEST
MENU.

4. Place the cursor on DIAGNOSTICS and press EN­TER. The Þrst diagnostic test mode (Signal Phase
or Ohms Sense High) is selected (displayed).

5. Perform the following steps to determine the bit
pattern at the control registers:

A. Refer to one of the following DIAGNOSTIC

Test Modes tables to determine the bit pattern
designator (A through X) for the selected func­tion/range:

Table 2-2 Ñ All functions except
Table 2-3 Ñ
Table 2-4 Ñ

ranges

B. Once the bit pattern designator is determined,

use Table 2-5 to determine the logic state of
each register bit.

Example: Assume the 20VDC range is selected
and the instrument is in the ÒSignal PhaseÓ of
DIAGNOSTICS. From Table 2-2, the bit pattern
designator is C. Table 2-5 provides the logic
states for bit pattern C.

6. Use the cursor keys to select the other diagnostic
test modes. The key scrolls forward through the

Ω

4 function; 20

Ω

4 function, 2k

Ω

and 200

Ω

, 20k

Ω

4

Ω

Ω

and 200k

ranges

Ω

2-7

Troubleshooting

test modes and the key scrolls backward.
Again, use the appropriate tables to determine the
bit pattern at the control registers.

7. When Þnished, press EXIT three times to back out

Table 2-2

DIAGNOSTICS test modes (all functions except Ω4)

Test mode Selected function Selected range Bit pattern

Signal Phase DCV 200mV

ACV, ACI and FREQ All E

DCI All F

Ω220Ω, 200Ω

TEMP RTD (open input) Ñ H

of the menu structure and return to the normal
measurement mode of operation.

8. If you wish to check another function/range, re­peat steps 1 through 7.

designator*

A
2V, 200V
20V
1000V

B
C
D

G

2kΩ-200MΩ
1GΩ

H

I

TEMP TC Ñ B

7V div by 1 * 1 All (except Ω4) All J
7V div by 1 * 1.5 All (except Ω4) All K
2V div by 1 * 5 All (except Ω4) All L
0V div by 1 * 1 All (except Ω4) All M
0V div by 1 * 5 All (except Ω4) All N
0V div by 1 * 50 All (except Ω4) All O
0V div by 1 * 1.5 All (except Ω4) All P
FE zero for 200mV All (except Ω4) All Q
FE zero for 2V All (except Ω4) All R

*Bit patterns are provided in Table 2-5.

2-8

Troubleshooting

Table 2-3

DIAGNOSTICS test modes (
and 200

Ω

ranges)

Ω

4 function; 20

Test mode Bit pattern

designator*

Ohms sense high G

7V div by 1 * 1 P

7V div by 1 * 1.5 Q

2V div by 1 * 5 R

0V div by 1 * 1 S

0V div by 1 * 5 T

0V div by 1 * 50 U

0V div by 1 * 1.5 V

Ohms sense minus W

FE zero for 2V X

*See Table 2-5 for bit patterns.

Table 2-4

Ω

DIAGNOSTICS test modes (
thru 200k

Ω

ranges)

Ω

4 function; 2k

Ω

Test mode Bit pattern

designator*

Ohms sense high H

7V div by 1 * 1 P

7V div by 1 * 1.5 Q

2V div by 1 * 5 R

0V div by 1 * 1 S

0V div by 1 * 5 T

0V div by 1 * 50 U

0V div by 1 * 1.5 V

FE zero for 200mV W

Ohms sense minus X

*See Table 2-5 for bit patterns.

2-9

2-10

Table 2-5

DIAGNOSTICS bit patterns (DC_STB registers)

Registers

Bit

pattern

Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1

A XX111011 01110111 01010101 01000100
B XX111101 01110111 01010101 01000100
C XX111111 00011110 01010101 01000100
D XX111110 01110111 01010101 01000100
E XX101101 01111111 01010101 01000100

F XX011011 01111111 01010101 01000100
G XX111011 01110111 11010101 01000100
H XX111101 01110111 11010101 01000100

I XX111110 01110111 11010101 01000100

J XX111110 01111011 01101010 10000100
K XX111111 01011011 01010101 01000100
L XX110101 01111111 01101010 10000100

M XX111110 00111111 01010101 01000100

N XX111101 00111111 01101010 10000100
O XX111011 00111111 01010101 01000100
P XX111111 00011111 01101010 10000100
Q XX111011 11110101 01010101 01000100
R XX111101 11110101 01101010 10000100

S 00111110 00111111 01101010 01010101
T 00111101 00111111 01010101 10101110
U 00111011 00111111 01101010 01010101
V 00111110 00011111 01010101 10101110

W 00111011 11110100 01101010 01010101

X 00111101 11110101 01010101 10101110

U303 U300 U800 U801

Troubleshooting

Troubleshooting

2.7 R1_STB and R2_STB shift registers

Table 2-6 and Table 2-7 are provided to allow you to
check logic levels on the R1_STB and R2_STB shift reg­isters (U302, U305, U307, U501, U530, U500 and U505)
for each basic measurement function (DCV, ACV, DCI,
ACI,

Ω

2 and

Ω

4) and range. The known bit pattern at
these registers can then be used for signal tracing
through the unit. Tables 2-11 and Table 2-12provide a
brief description of each register bit.

To use these tables, simply place the instrument in the
designated function and range and check the output of
the shift registers for the indicated bit pattern. The bit
patterns in these tables assume the following condi­tions:

NPLC > 0.01
AC Type = RMS or Average
Offset Compensated Ohms = Off
Current Measurement Mode = Normal (No In-Circuit I)

2-11

2-12

Troubleshooting

Table 2-6

Bit patterns for R1_STB registers

Function Range Registers

U302 U305 U307

Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1

DCV 200mV-20V

200V, 1000V

ACV All 01111111 11000000 11111010

DCI 200µA

2mA
20mA
200mA
2A

ACI 200µA

2mA
20mA
200mA
2A

Ω220Ω

200Ω, 2kΩ
20kΩ
200kΩ
2MΩ
20MΩ
200MΩ, 1GΩ

Ω420Ω

200Ω, 2kΩ
20kΩ
200kΩ

01111111
01111111

01111010
01110110
01101110
01011110
00111111

01111010
01110110
01101110
01011110
00111110

01111111
01111111
01111111
01111111
01111111
01111111
01111111

01111111
01111111
01111111
01111111

11110100
11000000

11000000
11000000
11000000
11000000
11000000

11000000
11000000
11000000
11000000
11000000

11110110
11110110
11110110
11110110
11111110
11111110
01111110

10110010
10110010
10110010
10110010

10011010
11011010

11011010
11011010
11011010
11011010
11011010

11011010
11011010
11011010
11011010
11011010

10011000
10011001
10011010
10011011
00011011
10011011
10011011

11011100
11011101
11011110
11011111

Table 2-7

Bit patterns for R2_STB registers

Registers

U501 U530

Function Range

DCV All 0110101000000000

ACV 200mV

2V
20V
200V
750V

DCI All 0110101000000000

ACI All 0110000110000000

Ω2, Ω4 All 0110101000000000

Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1

01110001
01110001
01110001
01110001
01110001

10000000
10000000
10000000
10000000
10000000

Registers

Troubleshooting

U500 U505

Range Range

DCV All 10100011 00000111

ACV 200mV

2V
20V
200V
750V

DCI All 10100111 00011111

ACI All 11101111 01001111

Ω2, Ω4 All 10100011 00000111

Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1

11101101
11101001
11101110
11101110
11101010

10011111
10111111
00011110
00011110
00011110

2-13

Troubleshooting

2.8 Display board checks

If the FRONT PANEL TESTS (paragraph 2.4) indicate
that there is a problem on the display board, use Table
2-8.

Circuit theory for the display is provided in paragraph

2.9.1.

Table 2-8

Display board checks

Step Item/component Required condition Remarks

1 FRONT PANEL TESTS Verify that all pixels operate Use SELF-TEST MENU selection

2 P1033, pins 4, 6, 14 and 16 5VAC, ±0.3VAC VFD Þlament

2.9 Power supply checks

Power supply problems can be checked out using Ta­ble 2-9.

3 P1033, pin 5 +5V, ±5% Digital +5V supply
4 P1033, pin 9 +60V, ±10% VFD +60V supply

5 P1033, pin 12 Goes low brießy on power-up,

then goes high

6 P1033, pin 2 4MHz square wave Controller 4MHz clock

7 P1033, pin 8 Pulse train every 1msec Control from main processor

8 P1033, pin 10 Brief pulse train when front

panel key is pressed

Microcontroller RESET line

Key down data sent to main pro­cessor.

2-14

Table 2-9

Power supply checks

Step Item/component Required condition Remarks

1 F100 line fuse Check continuity Remove to check

Troubleshooting

2 Line power Plugged into live receptacle,

power on

3 U108, pin 3 +5V, ±5% Reference to Common 3
4 U107, pin 3 +15V, ±0.75V Reference to COM
5 U102, pin 3 -15V, ±0.75V Reference to COM

6 CR109, +BS +34V to +38V Reference to Common 3

7 CR110, -BS -34V to -38V Reference to Common 3

8 U103, pin 3 ~+18V Reference to Isolated Common

9 U103, pin 2 +8V Reference to Isolated Common

10 U619, +5VC +5V, ±5% Reference to Digital Common
11 U629, pin 3` +5V, ±5% Reference to Digital Common

2.10 Documentation

The following information is provided to support the
troubleshooting tests and procedures previously cov­ered in this section of the manual. Figure 2-1 provides
an overall block diagram of the Model 2001 showing
the major circuit groups. Most circuits in the Model
2001 are tested and/or exercised by Built-in Test. A
short description for each of these tests explains how

that particular circuit operates. The display board and
the power supply are not tested by Built-in Test. Thus,
some basic theory is provided for these circuits in para­graphs 2.10.1 and 2.10.2.

Check for correct power up
sequence

2-15

Troubleshooting

Digital

55 Vdc 5 Vdc 5.5 Vac

Front

Panel

Controller

Front Panel Reset

Front Panel Clock

Front Panel Data Out

Front Panel Data In

68302

IEEE

Data Out

IEEE

Data

Trigger

(DMA)

In (ISR)

Software

Delay

IEEE-488 Bus

GPIB

56

Digital I/O

Trigger

F/R Status

DC SIG/REF

Signal

DC Input

ADC Data In

O

PTOIS

ADC Data In

DC/MUX FETS

Conditioning

CLK

CLK

ADC

DATA

DATA

TRMS,

AVE,

Amps

O

STB

PK

STB

TRG

Control

Data Out

FREQ Out

Signal

AC Input

Hardware

Trigger

AC FETS

(w/freq)

Conditioning

Select

Trigger

Logic

Scanner Control Out

Option

Scanner

FREQ In

External Trigger,

Power Supply

Meter Complete

Trigger Bus

Figure 2-1

Model 2001 overall block diagram

2-16

Amps

Sense HI

Sense LO

Scanner Output

Scanner

Inputs

Input HI

Input LO

Troubleshooting

2.10.1 Display board circuit theory

The following information provides some basic circuit
theory that can be used as an aide to troubleshoot the
display and keyboard.

Display microcontroller

U902 is the display microcontroller that controls the
VFD (vacuum ßuorescent display) and interprets key
data. The microcontroller has four peripheral I/O
ports that are used for the various control and read
functions.

Display data is serially transmitted to the microcon­troller from the digital board via the TXB line to the mi­crocontroller PD0 terminal. In a similar manner, key
data is serially sent back to the digital board through
the RXB line via PD1. The 4MHz clock for the micro­controller is generated on the digital board.

Vacuum fluorescent display

2.10.2 Power supply circuit theory

The following information provides some basic circuit
theory that can be used as an aide to troubleshoot the
power supply.

Pre-regulator circuit

The pre-regulator circuit regulates power to the trans­former. When power is applied to the instrument, a
power transformer secondary voltage (pins 12 and 13)
is rectiÞed (CR622), doubled (C624, C630, CR624 and
CR625) and applied to U619 which is a +5V regulator.
This +5V (+5VC) is used for the pre-regulator circuit.

The pre-regulator circuit monitors the voltage level on
C611 using an integrator (U627). The voltage on C611
(typically around 7.5V) is divided by three through
R712 and R713 and applied to the inverting input (pin

2) of the integrator. The +5V (+5VC) is divided by two
through R706 and R708. This 2.5V reference is applied
to the non-inverting input (pin 3) of the integrator.

DS901 is the VFD (vacuum ßuorescent display) mod­ule, which can display up to 49 characters. Each char-

acter is organized as a 5 × 7 matrix of dots or pixels and

includes a long under-bar segment to act as a cursor.

The display uses a common multiplexing scheme with
each character refreshed in sequence. U903 and U904
are the grid drivers, while U901 and U905 are the dot
drivers. Note that dot driver and grid driver data is se­rially transmitted from the microcontroller (PD3 and
PC1).

The VFD requires both +60VDC and 5VAC for the Þla­ments. These VFD voltages are supplied by U625,
which is located on the digital board.

Key matrix

The front panel keys (S901-S931) are organized into a
row-column matrix to minimize the number of micro­controller peripheral lines required to read the key­board. A key is read by strobing the columns and
reading all rows for each strobed column. Key down
data is interpreted by the display microcontroller and
sent back to the main microprocessor using proprietary
encoding schemes.

When the voltage on the inverting input of the integra­tor is less than the 2.5V reference on the non-inverting
input, the integrator output ramps in the positive di­rection. This positive ramp turns on Q608 which pulls
the CONT line low to digital common. With CONT
connected to common, current ßows through the pho­todiode of U100 and generates a positive voltage at the

gate of FET Q528. As Q528 turns on, the 470Ω resistor

(R100) becomes shunted and results in less effective re­sistance to the transformer. The resultant increase in
current (power) will increase the voltage on C611.

Conversely, when the voltage on the inverting input of
the integrator is more than the 2.5V reference, the inte­grator output ramps in the negative direction and be­gins to turn Q608 off. This will decrease current
through U100, decrease the positive voltage on Q528
and thus, increase the effective resistance to the trans­former. The resultant decrease in current (power) will
decrease the voltage of C611.

This constant regulation of effective resistance in series
with the transformer regulates the power delivered to
the instrument.

2-17