Keithley 2000rep schematic
Model 2000
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.
T o e xercise this w arranty, write or call your local K eithley representati v e, or contact K eithle y headquarters in
Cleveland, Ohio. You 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, nonrechargeable 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 B UYER’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 • 440-248-0400 • Fax: 440-248-6168 • http://www.k eithley.com
BELGIUM: Keithley Instruments B.V. Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02/363 00 40 • Fax: 02/363 00 64
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6/99
Model 2000 Multimeter
Repair Manual
©1995, Keithley Instruments, Inc.
All rights reserved.
Cleveland, Ohio, U.S.A.
Second Printing, March 1997
Document Number: 2000-902-01 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 Le vel letter increases alphabetically as the manual under goes 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 Re vision is created, all Addenda associated with the previous Re vision
of the manual are incorporated into the new Revision of the manual. Each ne w Revision includes
a revised copy of this print history page.
Revision A (Document Number 2000-902-01).................................................................May 1995
Revision B (Document Number 2000-902-01).............................................................. March 1997
All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.
Other brand 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 v oltages, there
are situations where hazardous conditions may be present.
This product is intended for use by qualified 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.
The types of product users are:
Responsible body is the individual or group responsible for the use and maintenance of equipment, and for en-
suring that operators are adequately trained.
Operators use the product for its intended function. They must be trained in electrical safety procedures and
proper use of the instrument. They must be protected from electric shock and contact with hazardous live circuits.
Maintenance personnel perform routine procedures on the product to keep it operating, for example, setting
the line voltage or replacing consumable materials. Maintenance procedures are described in the manual. The
procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.
Service personnel are trained to work on live circuits, and perform safe installations and repairs of products.
Only properly trained service personnel may perform installation and service procedures.
Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector
jacks or test fixtures. The American National Standards Institute (ANSI) states that a shock hazard e xists when
voltage levels greater than 30V RMS, 42.4V peak, or 60VDC are present. A good safety practice is to expect
that hazardous voltage is present in any unknown circuit before measuring.
Users of this product must be protected from electric shock at all times. The responsible body must ensure that
users are prevented access and/or insulated from every connection point. In some cases, connections must be
exposed to potential human contact. Product users in these circumstances must be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating at or above 1000 volts, no conductive part
of the circuit may be exposed.
As described in the International Electrotechnical Commission (IEC) Standard IEC 664, digital multimeter
measuring circuits (e.g., Keithley Models 175A, 199, 2000, 2001, 2002, and 2010) measuring circuits are Installation Category II. All other instruments’ signal terminals are Installation Category I and must not be connected to mains.
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 mains. When connecting sources to
switching cards, install protective devices to limit fault current and voltage to the card.
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 an y 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.
Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications
and operating information, and as shown on the instrument or test fixture panels, or switching card.
When fuses are used in a product, replace with same type and rating for continued protection against fire 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 fixture, 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, connect it to safety earth ground using the wire recommended in the user documentation.
!
The symbol on an instrument indicates that the user should refer to the operating instructions located in
the manual.
The symbol on an instrument shows that it can source or measure 1000 volts or more, including the combined effect of normal and common mode voltages. Use standard safety precautions to avoid personal contact
with these voltages.
The WARNING heading in a manual explains dangers that might result in personal injury or death. Always
read the associated information very carefully before performing the indicated procedure.
The CAUTION heading in a manual explains hazards that could damage the instrument. Such damage may
invalidate the warranty.
Instrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and all test cables.
To maintain protection from electric shock and fire, replacement components in mains circuits, including the
power transformer, test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses,
with applicable national safety approvals, may be used if the rating and type are the same. Other components
that are not safety related may be purchased from other suppliers as long as they are equivalent to the original
component. (Note that selected parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you are unsure about the applicability of a replacement component,
call a Keithley Instruments office for information.
T o clean the instrument, use a damp cloth or mild, water based cleaner . Clean the exterior of the instrument only .
Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument.
T able of Contents
1
Routine Maintenance
Introduction..........................................................................................1-2
Setting line voltage and replacing fuse................................................1-2
AMPS fuse replacement......................................................................1-4
2
T roubleshooting
Introduction..........................................................................................2-2
Repair considerations...........................................................................2-3
Power-on test.......................................................................................2-3
Front panel tests...................................................................................2-4
Principles of operation.........................................................................2-5
Display board checks.........................................................................2-11
Power supply checks..........................................................................2-11
Digital circuitry checks......................................................................2-12
Analog signal switching states...........................................................2-13
Built-In T est overview .......................................................................2-18
Built-In T est documentation..............................................................2-22
Disassembly
3
Introduction..........................................................................................3-2
Handling and cleaning.........................................................................3-3
Static sensitive devices........................................................................3-4
Assembly drawings..............................................................................3-4
Case cover removal..............................................................................3-5
Changing trigger link lines ..................................................................3-6
Motherboard removal ..........................................................................3-7
Front panel disassembly ......................................................................3-8
Main CPU firmware replacement........................................................3-9
Removing power components ...........................................................3-10
Instrument re-assembly......................................................................3-12
Replaceable Parts
4
Introduction..........................................................................................4-2
Parts lists..............................................................................................4-2
Ordering information...........................................................................4-2
Factory service.....................................................................................4-3
Component layouts..............................................................................4-3
A
Specifications
............................................................................................................A-1
List of Illustrations
1
Routine Maintenance
Power module......................................................................................1-3
2
T roubleshooting
Power supply block diagram...............................................................2-6
Digital circuitry block diagram ...........................................................2-7
Analog circuitry block diagram...........................................................2-9
Disassembly
3
Trigger link line connections...............................................................3-6
Ω
Ω
Ω 2/ Ω
Ω
Ω
List of T ables
1
Routine Maintenance
Fuse rating ...........................................................................................1-3
2
T roubleshooting
Power supply circuits...........................................................................2-7
Display board checks.........................................................................2-11
Power supply checks..........................................................................2-11
Digital circuitry checks......................................................................2-12
DCV signal switching........................................................................2-13
ACV and FREQ signal switching......................................................2-13
2 signal switching...........................................................................2-14
4 signal switching...........................................................................2-14
DCA signal switching........................................................................2-15
ACA signal switching........................................................................2-15
DCV signal multiplexing and gain....................................................2-16
ACV and ACA signal multiplexing and gain.....................................2-16
DCA signal multiplexing and gain....................................................2-16
2 signal multiplexing and gain........................................................2-16
4 signal multiplexing and gain........................................................2-17
Circuit section location for switching devices...................................2-17
Built-In T est summary.......................................................................2-19
4 reference switching................................................................2-15
1
Routine
Maintenance
1-2 Routine Maintenance
Introduction
The information in this section deals with routine type maintenance that can be performed by
the operator. This information is arranged as follows:
• Setting line voltage and replacing fuse — Explains how to select the alternate po wer line
voltage setting, and how to replace a blown power line fuse.
• Amps fuse replacement — Explains how to replace a blown current fuse.
Setting line voltage and replacing fuse
A rear panel fuse located next to the A C receptacle (in the power module) protects the power
line input of the instrument. If the line voltage setting needs to be changed or the line fuse needs
to be replaced, perform the following steps.
W ARNING Disconnect the line cord at the rear panel and remove all test leads connected to the instru-
ment (front and rear) before replacing the line fuse or changing the line voltage setting.
1. Place the tip of a flat-blade screwdriv er into the po wer module by the fuse holder assembly (see Figure 1-1). Gently push in and to the left. Release pressure on the assembly and
its internal spring will push it out of the power module.
2. Remove the fuse and replace it with the type listed in Table 1-1.
CAUTION For continued protection against fire or instrument damage, only replace
fuse with the type and rating listed. If the instrument repeatedly blows fuses,
locate and correct the cause of the trouble before replacing the fuse.
3. If configuring the instrument for a different line voltage, remo ve the line voltage selector
from the assembly and rotate it to the proper position. When the selector is installed into
the fuse holder assembly, the correct line voltage appears inverted in the window.
4. Install the fuse holder assembly into the power module by pushing it in until it locks in
place.
WARNING:NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
WARNING:NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
CAUTION:FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
CAUTION:FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
×
Routine Maintenance 1-3
Figure 1-2
Power module
Model 2000
HI
1000V
350V
PEAK
!
PEAK
LO
500V
1
PEAK
SENSE
INPUT
Ω 4W
!
2
MADE IN
U.S.A.
IEEE-488
(CHANGE IEEE ADDRESS
TRIGGER
LINK
!
3 5
VMC
4 6
EXT TRIG
!
FUSE LINE
250mAT
100 VAC
(SB)
120 VAC
220 VAC
125mAT
240 VAC
(SB)
FROM FRONT PANEL)
RS232
120
LINE RATING
50, 60
400HZ
17 VA MAX
Line Voltage Selector
Fuse
Spring
Fuse Holder Assembly
Table 1-1
Fuse rating
Line voltage Fuse rating Keithley part no.
100/120V
220/240V
0.25A slow-blow 5 × 20mm
0.125A slow-blow 5
20mm
FU-96-4
FU-91
220
240
120
100
Window
1-4 Routine Maintenance
AMPS fuse replacement
WARNING Make sure the instrument is disconnected from the power line and other equipment before
replacing the AMPS fuse.
1. Turn off the power and disconnect the power line and test leads.
2. From the front panel, gently push in the AMPS jack with your thumb and rotate the fuse
carrier one-quarter turn counter-clockwise. Release pressure on the jack and its internal
spring will push the fuse carrier out of the socket.
3. Remove the fuse and replace it with the same type 3A, 250V, fast blow: Keithley
part number FU-99-1.
CAUTION Do not use a fuse with a higher current rating than specified or instrument
damage may occur. If the instrument repeatedly blows fuses, locate and correct the cause of the trouble before replacing the fuse.
4. Install the new fuse by reversing the procedure.
2
Troubleshooting
2-2 Troubleshooting
Introduction
WARNING The information in this section is intended for qualified service personnel.
Some of these procedures may expose you to hazardous voltages. Do not per form these hazardous procedures unless you are qualified to do so.
This section of the manual will assist you in troubleshooting the Model 2000. 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:
• Repair considerations — Covers some considerations that should be noted before making any repairs to the Model 2000.
• Power-on test — Describes the tests that are performed on memory elements each time
the instrument is turned on.
• Front panel tests — Provides the procedures to test the functionality of the front panel
keys and the display.
• Principles of operation — Provides support documentation for the various troubleshooting tests and procedures. Included is some basic circuit theory for the display board,
power supply, digital circuitry and analog circuitry.
• Display board checks — Provides display board checks that can be made if front panel
tests fail.
• Power supply checks — Provides po wer supply checks that can be made if the inte grity
of the power supply is questionable.
• Digital circuitry checks — Provides some basic checks for the digital circuitry.
• Analog signal switching states — Provides tables to check switching states of various
relays, FETs, analog switches and the A/D multiplexer for the basic measurement functions and ranges.
• Built-in test overview — Summarizes the b uilt-in tests, which can be used to test and e xercise the various digital and analog circuits.
• Built-in test documentation — Provides a detailed analysis of each built-in test.
Troubleshooting 2-3
Repair considerations
Before making any repairs to the Model 2000, be sure to read the following considerations.
CAUTION The PC-boards are built using surface mount techniques and require special-
ized equipment and skills for repair. If you are not equipped and/or qualified,
it is strongly recommended that you send the unit back to the factory for repairs or limit repairs to the PC-board replacement level. Without proper
equipment and training, you could damage a PC-board beyond repair.
1. Repairs will require various degrees of disassembly. However, it is recommended that
the Front Panel Tests and Built-In-Test be performed prior to any disassembly. The disassembly instructions for the Model 2000 are contained in Section 3 of this manual.
2. Do not make repairs to surface mount PC-boards unless equipped and qualified 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 Section 3.
4. Many CMOS devices are installed in the Model 2000. These static-sensitive devices require special handling as explained in Section 3.
5. Anytime a circuit board is removed or a component is replaced, the Model 2000
must be recalibrated.
Power-on test
During the power-on sequence, the Model 2000 will perform a checksum test on its EPROM
(U156 and U157) and test its RAM (U151 and U152). If one of these tests fails the instrument
will lock up.
▲
▲
2-4 Troubleshooting
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 ev ent of a test failure, refer to “Display Board Checks” for details on troubleshooting the display board.
KEY test
The KEY test allows you to check the functionality of each front panel key. Perform the following steps to run the KEY test:
1. Press SHIFT and then TEST to access the self-test options.
2. Use the
3. Press ENTER to start the test. When a ke y is pressed, the label name for that key is displayed to indicate that it is functioning properly. When the key is released, the message
“NO KEY PRESS” is displayed.
4. Pressing EXIT tests the EXIT key . Ho we v er, the second consecutive press of EXIT
aborts the test and returns the instrument to normal operation.
or ▼ key to display “TEST: KEY”.
DISP test
cent display is working properly. Perform the following steps to run the display test:
The display test allows you to verify that each pixel and annunciator in the vacuum fluores-
1. Press SHIFT and then TEST to access the self-test options.
2. Use the
3. Press ENTER to start the test. There are four parts to the display test. Each time ENTER
is pressed, the next part of the test sequence is selected. The four parts of the test sequence are as follows:
A. All annunciators are displayed.
B. The pixels of each digit are sequentially displayed.
C. The 12 digits (and annunciators) are sequentially displayed.
D. The annunciators located at either end of the display are sequentially displayed.
4. When finished, abort the display test by pressing EXIT. The instrument returns to
normal operation.
or ▼ key to display “TEST: DISP”.
Principles of operation
The following information is provided to support the troubleshooting tests and procedures
covered in this section of the manual. Refer to the following block diagrams:
Block Diagrams:
Figure 2-1 — Power supply block diagram
Figure 2-2 — Digital circuitry block diagram
Figure 2-3 — Analog circuitry block diagram
Display board
Troubleshooting 2-5
Microcontroller
U401 is the display board microcontroller that controls the display and interprets key data.
The microcontroller uses three internal, peripheral I/O ports for the various control and read
functions.
Display data is serially transmitted to the microcontroller from the digital section via the TXB
line to the microcontroller RDI terminal. In a similar manner, key data is serially sent back to
the digital section through the RXB line via TDO. The 4MHz clock for the microcontroller is
generated by crystal Y401.
Display
DS401 is the display module, which can display up to 12 alpha-numeric characters and the
various annunciators.
The display uses a common multiplexing scheme with each character refreshed in sequence.
U402 and U403 are the drivers for the display characters and annunciators. Note that data for
the drivers are serially transmitted from the microcontroller (MOSI and PC1).
Filament voltage for the display is derived from the power supply transformer (F1 and F2).
The display drivers require +37VDC and +5VDC, which are supplied by U144 (+5VD) and
U101 (+37V).
2-6 Troubleshooting
Key matrix
The front panel keys (S401-S430) are organized into a row-column matrix to minimize the
number of microcontroller peripheral lines required to read the keyboard. A k ey is read by strobing the columns and reading all rows for each strobed column. K e y down data is interpreted by
the display microcontroller and sent back to the main microprocessor using proprietary encoding schemes.
Power supply
The following information provides some basic circuit theory that can be used as an aid to
troubleshoot the power supply. A block diagram of the power supply is shown in Figure 2-1.
Figure 2-1
Power supply
block diagram
+5VD
D Common
+37V
D Common
+15V
A Common
-15V
+5V, +5VRL
A Common
Fuse
Power
Switch
Line
Voltage
Switch
Power
Transformer
CR104
C128, C156
U144
CR116, CR117
C104, C108
U101
CR102
C131, C148
U119, U125
CR103
C146
U124
AC power is applied to the AC power module receptacle (J1009). Power is routed through the
line fuse and line voltage selection switch of the power module to the power transformer. The
power transformer has a total of four secondary windings for the various supplies.
AC voltage for the display fi laments is taken from a power transformer secondary at F1 and
F2, and then routed to the display board.
Each DC supply uses a bridge rectifier, a capaciti v e filter arrangement and a regulator . Table
2-1 summarizes rectifier, filter and regulator circuits for the various supplies.
Table 2-1
Power supply circuits
Supply Rectifier Filter Regulator
Troubleshooting 2-7
Digital circuitry
Figure 2-2
Digital circuitry
block diagram
+5VD
+37V
+15V
-15V
+5V, +5VRL
CR104
CR116, CR117
CR102
CR102
CR103
C128, C156
C104, C108
C148
C131
C146
U144
U101
U125
U119
U124
Refer to Figure 2-2 for the following discussion on digital circuitry.
RAM
U151, U152
IN
OUT
Data IN
Data OUT
Analog
Circuitry
(See Figure 2-3)
XADTX
XADCLK
XADTS
XADRX
Scan Control
U146, U164
Trigger
O
P
T
O
I
S
O
AT101
U150
U155
NVRAM
U136
ADTX
ADCLK
ADTS
ADRXB
TRIG IN
TRIG OUT
ROM
U156, U157
68306
µP
U135
Display Board
Controller
U401
XTAL
Y101
RS-232
U159
GPIB
U158, U160,
U161
Keypad
RS-232
Port
Display
DS401
IEEE-488
Bus
Trigger
Link
2-8 Troubleshooting
Microprocessor
U135 is a 68306 microprocessor that oversees all operating aspects of the instrument. The
MPU has a 16-bit data bus and provides an 18-bit address b us. It also has parallel and serial ports
for controlling various circuits. For example, the RXDA, TXDA, RXDB and TXDB lines are
used for the RS-232 interface.
The MPU clock frequency of 14.7456MHz is controlled by crystal Y101. MPU RESET is
performed momentarily (through C241) on power-up by the +5VD power supply.
Memory circuits
ROMs U156 and U157 store the firmware code for instrument operation. U157 stores the D0D7 bits of each data word, and U156 stores the D8-D15 bits.
RAMS U151 and U152 provide temporary operating storage. U152 stores the D0-D7 bits of
each data word, and U151 stores the D8-D15 bits.
Semi-permanent storage facilities include NVRAM U136. This IC stores such information as
instrument setup and calibration constants. Data transmission from this device is done in a serial
fashion.
RS-232 interface
Serial data transmission and reception is performed by the TXDB and RXDB lines of the
MPU. U159 provides the necessary voltage level conversion for the RS-232 interface port.
IEEE-488 interface
U158, U160 and U161 make up the IEEE-488 interface. U158, a 9914A GPIA, takes care of
routine bus overhead such as handshaking, while U160 and U161 provide the necessary buffering and drive capabilities.
T rigger circuits
Buffering for Trigger Link input and output is performed by U146. T rigger input and output
is controlled by the IRQ4 and PB3 lines of the MPU. U164 provides additional logic for the trigger input to minimize MPU control overhead.
At the factory, trigger output is connected to line 1 of the Trigger Link connector (resistor
R267 installed). Trigger input is connected to line 2 of the T rigger Link connector (resistor R270
installed).
Analog circuitry
Refer to Figure 2-3 for the following discussion on analog circuitry.
Ω
Ω
Troubleshooting 2-9
Figure 2-3
Analog circuitry
block diagram
AMPS
DCA
ACA
AC Switching
K102, U102, U103, U105,
U112, U118, U111, U110
ACV,
FREQ
SSP*
Ohms I-Source
U133, Q123, Q125,
Q124, Q126, Q119,
Q120, U123
Scanner Control
Gain
&
DCV
OHMS
DCV & Ohms
Switching
K101, Q104, Q105,
Q108, Q113, U115
X1
Buffer
U113
BUFCOM
A/D
MUX &
Gain
U163, U166
U129, U132
ADC
U165
Digital
Circuitry
(See Figure 2-2)
INPUT
HI
R117, Q109,
Q114, Q136
SENSE
HI
SENSE
LO
Scanner Output
Scanner
Inputs
K103, R158, R205
Q101, Q102
DCV
Divider
DCV/100
Q121, U126
Scanner
Option
*Solid State Protection
Current
Shunts
X1 Buffer
INPUT HI
INPUT HI protection is provided by the SSP (solid state protection) circuit. The SSP is primarily made up of Q101 and Q102. An overload condition opens Q101 and Q102. This disconnects the analog input signal from the rest of the analog circuit.
Note that for the 100VDC and 1000VDC ranges, Q101 and Q102 of the SSP are open. The
DC voltage signal is routed through the DCV Divider (Q114 and Q136 on) to the DCV switching circuit.
AMPS input
The ACA or DCA input signal is applied to the Current Shunt circuit, which is made up of
K103, R158 and R205. For the 10mADC range, 10.1
put. Relay K103 is energized (on) to select the shunts. For all other DCA ranges, and all ACA
ranges, 0.1
(R158) is shunted across the input (K103 off).
The A CA signal is then sent to the A C Switching & Gain circuit, while the DCA signal is routed directly to the A/D MUX & Gain circuit.
(R158 + R205) is shunted across the in-
2-10 Troubleshooting
Signal switching
Signal switching for DCV and OHMS is done by the DCV & Ohms Switching circuit. FETs
Q113, Q105, Q104 and Q108 connect the DCV or ohms signal to the
2-5 through 2-8 show the switching states of these FETs for the v arious DCV and OHMS ranges.)
Note that the reference current for OHMS is generated by the Ohms I-Source circuit. For 4wire ohms measurements, SENSE LO is connected to the circuit by turning on Q121.
Signal switching and gain for ACV, FREQ and ACA is done by the AC Switching & Gain
circuit, which is primarily made up of K102, U102, U103, U105, U112, U118, U111 and U110.
Tables 2-6 and 2-11 show the switching states for these AC signals. Note that U111 is used for
frequency adjustment. The states of these analog switches vary from unit to unit.
×
1 buffer (U113). (Tables
Multiplexer and A/D converter
All input signals, except FREQ, are routed to the A/D MUX & Gain circuit. The multiplex er
(U163) switches the various signals for measurement. In addition to the input signal, the multiplexer also switches among reference and zero signals at v arious phases of the measurement cycle.
When the input signal is selected by the MUX, it is amplified by U132 and U166. Tables 212 through 2-16 identify the input signal lines (S3, S4, S6 or S7) of the multiplexer for the various functions and ranges. These tables also provide the switch states of U129, which determine
the gain for U132 and U166.
The multiplexed signals of the measurement cycle are routed to the A/D Converter (U165)
where it converts the analog signals to digital form. The digital signals are then routed through
an opto-isolator to the MPU to calculate a reading.
Display board checks
If the front panel DISP test indicates that there is a problem on the display board, use Table
2-2. See “Principles of Operation” for display circuit theory.
Table 2-2
Display board checks
Step Item/component Required condition Remarks
Troubleshooting 2-11
Front panel DISP test.
1
P1005, pin 5
2
P1005, pin 9
3
U401, pin 1
4
U401, pin 43
5
U401, pin 32
6
U401, pin 33
7
Power supply checks
Power supply problems can be checked out using Table 2-3. See “Principles of Operation”
for circuit theory on the power supply.
Table 2-3
Power supply checks
Step Item/component Required condition Remarks
1
Line fuse
2
Line voltage
3
Line power
4
U144, pin2
5
U101, pin 7
6
U125, pin 3
7
U119, pin 3
8
U124, pin 3
Verify that all pixels operate.
+5V +/-5%
+37V +/-5%
Goes low briefly on power up,
then goes low.
4MHz square wave.
Pulse train every 1msec.
Brief pulse train when front
panel key pressed.
Check continuity.
120V/240V as required.
Plugged into live receptacle,
power on.
+5V +/-5%
+37V +/-5%
+15V +/-5%
-15V +/-5%
+5V +/-5%
Use front panel display test.
Digital +5V supply.
Display +37V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main
processor.
Remove to check.
Check power module position.
Check for correct power-up
sequence.
+5VD, referenced to Common D.
+37V, referenced to Common D.
+15V, referenced to Common A.
-15V, referenced to Common A.
+5VRL, referenced to Common A.
2-12 Troubleshooting
Digital circuitry checks
Digital circuit problems can be checked out using Table 2-4. See “Principles of Operation”
for digital circuit.
Table 2-4
Digital circuitry checks
Step Item/component Required condition Remarks
Power-on test
1
U152 pin 16
2
U152 pin 32
3
U135 pin 48
4
U135, lines A1 thru A23
5
U135, lines D1 thru D15
6
U135 pin 44
7
U159 pin 13
8
U159 pin 14
9
U158 pins 34-42
10
U158 pins 26-31
11
U158 pin 24
12
U158 pin 25
13
U135 pin 84
14
U135 pin 91
15
U135 pin 90
16
U135 pin 89
17
RAM OK, ROM OK.
Digital common.
+5V
Low on power-up, then goes
high.
Check for stuck bits.
Check for stuck bits.
14.7456MHz
Pulse train during RS-232 I/O.
Pulse train during RS-232 I/O.
Pulse train during IEEE-488 I/O.
Pulses during IEEE-488 I/O.
Low with remote enabled.
Low during interface clear.
Pulse train.
Pulse train.
Pulse train.
Pulse train.
Verify that RAM and
ROM are functional.
All signals referenced
to digital common.
Digital logic supply.
MPU RESET line.
MPU address bus.
MPU data bus.
MPU clock.
RS-232 RX line.
RS-232 TX line.
IEEE-488 data bus.
IEEE-488 command
lines.
IEEE-488 REN line.
IEEE-488 IFC line.
ADRXB
ADTX
ADCLK
ADTS
Analog signal switching states
Tables 2-5 through 2-11 provide switching states of the various relays, FETs and analog
switches for the basic measurement functions and ranges. These tables can be used to assist in
tracing an analog signal from the input to the A/D multiplexer.
Table 2-5
DCV signal switching
Range Q101 Q102 Q114 Q136 Q109 K101* Q113 Q105 Q104 Q108 Q121
OFF
OFF
ON
1V
10V
100V
ON
ON
ON
ON
ON
OFF
OFF
OFF
OFF
Pin 3 switched to Pin 4
OFF
OFF
ON
ON
OFF
OFF
ON
ON
100mV
1000V
*K101 set states: Pin 8 switched to Pin 7
OFF
OFF
OFF
OFF
OFF
SET
SET
SET
SET
SET
Troubleshooting 2-13
ON
OFF
ON
OFF
OFF
ON
OFF
ON
OFF
OFF
ON
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
Table 2-6
ACV and FREQ signal switching
Range Q101 Q102 K101* K102*
RESET
ON
1V
10V
100V
750V
ON
ON
ON
ON
ON
ON
ON
ON
ON
RESET
RESET
RESET
RESET
100mV
*K101 and K102 reset states: Pin 8 switched to Pin 9
K101 and K102 set states: Pin 8 switched to Pin 7
RESET
RESET
SET
SET
SET
Pin 3 switched to Pin 2
Pin 3 switched to Pin 4
U103
pin 8
ON
ON
OFF
OFF
OFF
U103
pin 9
ON
ON
OFF
OFF
OFF
U105
pin 9
OFF
OFF
ON
ON
ON
U105
pin 8
OFF
OFF
OFF
OFF
ON
U103
pin 16
OFF
ON
OFF
ON
OFF
U103
pin 1
ON
OFF
ON
OFF
OFF
U105
pin 1
ON
OFF
ON
OFF
OFF
U111
pin 16
OFF
OFF
OFF
OFF
OFF
2-14 Troubleshooting
Table 2-7
Ω
2 signal switching
Range Q101 Q102 Q114 Q136 Q109 K101* K102* Q113 Q105 Q104 Q108 Q121
100 Ω
ON
ON
ON
10k Ω
100k Ω
10M Ω
100M Ω
*K101 set states: Pin 8 switched to Pin 7
K102 reset states: Pin 8 switched to Pin 9
ON
ON
ON
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
Pin 3 switched to Pin 4
Pin 3 switched to Pin 2
OFF
OFF
OFF
OFF
OFF
ON
ON
SET
SET
SET
SET
SET
SET
SET
RESET
RESET
RESET
RESET
RESET
RESET
RESET
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
ON
ON
ON
ON
1k Ω
1M Ω
1k Ω
1M Ω
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
ON
OFF
OFF
Table 2-8
Ω
4 signal switching
Range Q101 Q102 Q114 Q136 Q109 K101* Q113 Q105 Q104 Q108 Q121
ON
OFF
OFF
OFF
100 Ω
10k Ω
100k Ω
10M Ω
100M Ω
*K101 set states: Pin 8 switched to Pin 7
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
Pin 3 switched to Pin 4
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
SET
SET
SET
SET
SET
SET
SET
ON
ON
ON
ON
ON
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
ON
ON
ON
Table 2-9
Ω
2/
Ω
4 reference switching
100 Ω
10k Ω
U133
/.7V
OFF
OFF
OFF
ON
ON
OFF
OFF
Range
100k Ω
10M Ω
100M Ω
U133
Q123 Q125 Q124 Q126 Q120
/7V
OFF
ON
ON
ON
OFF
ON
ON
ON
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
OFF
ON
ON
ON
ON
ON
ON
ON
ON
ON
ON
OFF
OFF
1k Ω
Troubleshooting 2-15
1M Ω
Table 2-10
DCA signal switching
Range K103
ON
10mA
1A
3A
OFF
OFF
OFF
100mA
Table 2-11
ACA signal switching
Range K103
1A3AOFF
OFFONONONON
T ables 2-12 through 2-16 can be used to trace the analog signal through the A/D multiplexer
(U163) to the final amplifier stage. These tables show the MUX lines (S3, S4, S6, S7) that are
selected for measurement during the SIGNAL phase of the multiplexing cycle. Also included
are switching states of analog switches (U129) that set up the gain for the final amplifier stage
(U166).
U105
pin 16
U105
pin 1
U111
pin 16
OFFONOFF
U105
pin 8
OFF
U103
pin 16
OFF
OFF
U103
pin 1
OFF
OFF
2-16 Troubleshooting
Table 2-12
DCV signal multiplexing and gain
×
× 10 × 1 ×
Range
100mV
10V
100V
1000V
1V
Signal
(U163)
S4
S4
S4
S4
S4
U129
pin 1
OFF
OFF
ON
OFF
ON
U129
pin 8
OFF
ON
OFF
ON
OFF
U129
pin 9
ON
OFF
OFF
OFF
OFF
Table 2-13
ACV and ACA signal multiplexing and gain
Range
All S3 ON OFF OFF ×1
Signal
(U163)
U129
pin 1
U129
pin 8
U129
pin 9
Table 2-14
DCA signal multiplexing and gain
Range
10mA
100mA
1A
3A
Signal
(U163)
S6
S6
S6
S6
U129
pin 1
OFF
OFF
OFF
OFF
U129
pin 8
OFF
OFF
OFF
ON
U129
pin 9
ON
ON
ON
OFF
Gain
(U166)
100
10
×1
Gain
(U166)
Gain
(U166)
×100
×100
×100
×10
Table 2-15
Ω
2 signal multiplexing and gain
Range
100Ω
1kΩ
10kΩ
100kΩ
1MΩ
10MΩ
100MΩ
Signal
(U163)
S4
S4
S4
S4
S4
S4
S4
U29 pin 1U129
OFF
OFF
OFF
OFF
ON
ON
ON
pin 8
OFF
ON
ON
ON
OFF
OFF
OFF
U129
pin 9
ON
OFF
OFF
OFF
OFF
OFF
OFF
Gain
(U166)
×100
×10
×10
×10
×1
×1
×1
Table 2-16
Ω
4 signal multiplexing and gain
Troubleshooting 2-17
100Ω
1kΩ
10kΩ
1MΩ
Signal
(U163)
S4 then S7
S4 then S7
S4 then S7
S4 then S7
S4 then S7
S4 then S7
S4 then S7
Range
100kΩ
10MΩ
100MΩ
Figure 2-3 provides a block diagram of the analog circuitry. Table 2-17 is provided to show
where the various switching devices are located in the block diagram.
U129
pin 1
OFF
OFF
OFF
OFF
ON
ON
ON
U129
pin 8
OFF
ON
ON
ON
OFF
OFF
OFF
U129
pin 9
ON
OFF
OFF
OFF
OFF
OFF
OFF
Gain
(U166)
×100
×10
×10
×10
×1
×1
×1
Table 2-17
Circuit section locations for switching devices
Switching devices
Q101, Q102
Q114, Q136, Q109
K101, Q113, Q105, Q104, Q108
Q121
K102, U103, U105, U111
U133, Q123, Q125, Q124,
Q126, Q120
K103
U163, U129
Analog circuit section
(see Figure 2-3)
SSP (Solid State Protection)
DCV Divider
DCV & Ohms Switching
Sense LO
AC Switching & Gain
Ohms I-Source
Current Shunts
A/D Mux & Gain
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