Keithley 247 Service manual

Model 247

High Voltage Supply

Instruction Manual

Contains Operating and Servicing Information

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year 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 Keithley representative, or contact Keithley 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.

LIMITATION OF WARRANTY

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 WARRAN

TIES, 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, INDI-

RECT, 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.

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Model 247 High Voltage Supply

Instruction Manual

Q 1990, Keithley Instruments, Inc.

Test Instrumentation Group

All rights reserved.

Cleveland, Ohio, U.S.A.

December 1992, Sixth Printing

Document Number: 31834 Rev. F

AU KeithIey 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 Model 247 High Voltage Supply.

The Model 247 High Voltage Supply is intended for use by qualified personnel who recognize shock hazards and are
familiar with the safety precautions required to avoid possible injury. Read over the instruction manual carefully before
using the instrument.

Exercise extreme caution when a shock hazard is present. Lethal voltages may be present on the test fixture or the supply
output connector. The American National Standards Jnstitute (ANSI) states the a shock hazard exists when voltage lev­els greater than3OV RMS or 42.4V peak are present. A good safety practice is to expect that hazardous voltage is present

in any unknown circuit before measuring.

Inspect the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.

For maximum safety, do not touch the voltage supply, test fixture, test cables or any other insfnunents while power is
applied to the circuit under test. Turn off all power and discharge any capacitorsbefore connecting or disconnecting
cables or jumpers.

Do not touch any object which 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 with-

standing the voltage being measured.

Instrumentation and accessories should not be connected to humans.

The
Instruction Manual.

symbol on a Model 247 indicates that 1OOOV or more may be present on the terminals. Refer to the Model 247

L

Model 247

High Voltage Power Supply

OUTPUT:

Voltage: 0 to 3kV DC
Currentz 6mA DC maximum.
Polarity: Positive or negative with respect to chassis.

ACCUI&4CY: (W-28°C): f (0.25% of setting t 1.5V DC) from 1% to 100% of maximum

output voltage.
RESOLUTION: Dial graduations of 200mV.
STABILITY: &O.Ol% of setting/hr.; fo.OZ% of setting/b hrs., at constant temperature after

r+hour warm-up.
TEMPEIUTURE COEFFICIENT (W’-18°C & 28”-50°C): sOppm/“C
LINE REGULATIONz 0.001% voltage change for 10% line variation.
LOAD REGULATION: 0.005% voltage change from no load to full load.
RIPPLEANDNOISE:3.5mVrms,lOmVp-p@3kV,6mA;lmV~,3mVp-p@lkV,lmA,

lOHz-1OOkHz
SE’ITLING TIME: 4 seconds to within 1V with full resistive load.
OVERLOAD PROTECTIONr Short circuit proof, arc protected, self restoring.
METER Monitors voltage output.
ENVIRONMENT:

Operating: 0’ to 50°C, 0 to 80% relative humidity up to 35°C
Storage: -40° to 75°C

CONNECTORz Rear panel, MI-IV Type LJG931/U.
POWER: 90-125V/180-25OV, 50-6OHz,13OVA.
DIMENSIONS,WEIG~:483mmwidex89mmhighx273~deep(l9inx3~/~in.x103/4

in.), excluding handles. Four holes spaced for rack mounting. Net weight 5.9kg (13 Ibs.).
ACCESSORIES SUPPLIEIX Instruction manual, UG932/U mating connector, mounting

feet for bench operation.

Specifications subject to change without notice.

Table of Contents

SECTION 1

1.1

1.2

1.3

1.4

1.5 W~INFoRMATION....................................................l- 2

- General Information

PURPOSEOFEQUIPMENT

DESCRIPTION
SPECIFICATIONS
sAFETYsYMEioLsANDTERMs..

................................................................

.............................................................

....................................................

................................................

..I- 1

l-l
l-l
l- 1

SECTION 2 - Operation

2.1

2.2 FRONTl?ANELCONTROLSANDTERMlNALS

2.3 REAR PANEL CONNECTORS AND TERMINALS

2.4

2.5

2.6
27

2.8 APPLICATIONS

2.8.1

2.8.2

2.8.3

INSTALLATION

l?REPAlK!JONFORUSE

INPUTPOWER ...............................................................

CURRENTLIMITING
HIGH VOLTAGE OUTPUT

Application of 247 wit& Photomultipliers
Application of 247 to Resisfivify Measurements
Application of 247 with Ionization Chambers

..............................................................

.....................................................

........................................................

......................................................

............................................................... 2-4

..........................................

....................................

.....................................

......................................

.......................................

2-l

..2- 1

2-2

..2- 3

2-3

..2- 3

2-3

2-4
2-4
2-4

SECTION 3 - Theory of Operation

3.1

3.2

FUNCTIONALDESCRTMTON
CIRCUtTDESCIUI’TION

......................................................

SECTION 4 - Maintenance

4.1

4.2

4.3 PREPARATION FORMEAS

4.4

4.5 PERFORMANCETESTS

4.6

INTRODUcTloN .............................................................. 4-l

RECOMMENDED TEST EQUIPMENT

UREMENTS ............................................ 4-2

CALIBRATION ADJUSTMENTS .................................................. 4-2

.........................................................

TROUJ3LESHOOTlNG PROCEDURE ..

SECTION 5 - Replaceable Parts

5.1 INTRODUCTION

5.2

5.3

ORDERINGINFORMATION

FACTORYSERVICE............................................................5- 1

..............................................................

.....................................................

....................................................

..............................................

f.

...........................................

3-l

..3- 1

4-l

4-2
4-3

5-l
5-l

SECTION 4 - Maintenance

List of Tables

Table 41

Recommended Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

SECTION 2 - Operation

List of Illustrations

Figure 2-1
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6

Model 247 Front Panel
Mode1247RearPanel

Connector and Cable Assembly

PhotomultiplierCircuit...................................- .................

Resistivity Measurement
Ionization Chamber Circuit

.....................................................

......................................................

SECTION 3 - Theory of Operation

Figure 3-l

High Voltage Power Supply Block Diagram

SECTION 4 - Maintenance

Figure 41

Model 247 Exploded View

..............................................

....................................................

..................................................

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-l

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2-2
2-2
2-4
2-4
2-4
24

SECTION 1

General Information

1 .I PURPOSE OF EQUIPMENT

The Model 247 is a regulated precision laboratory high

voltage power supply. It provides the low noise, excel­lent line regulation and high stability that are essential for
the most rigid measurement requirements.

1.2 DESCRIPTION

The Model 247 is a precision regulated linear power sup­ply with a maximum output voltage of 3kV. The units
consist of a DC power supply which converts the AC line
power to a low DC voltage and a DC converter which
generates the high DC output voltage. Low voltage elec­tronic solid-state circuitry is mounted on the plug-in PCB
100, and the high voltage assembly is fully encapsulated
for reliable, arc-free, operation.

The unit is fully enclosed and designed to mount in a
standard 19” rack. The unit may also be used in benchtop
applications using the rubber feet supplied.

1.3 SPECIFICATIONS

For Model247 detailed specifications, refer to the specifi­cations that precede this section.

1.4 SAFETY SYMBOLS AND TERMS

Safety symbols used in this manual are as follows:

Thesymbol ’ Q on the instrument denotes that the user
should refer to the operating instructions.

The symbol on the instrument denotes that 1OOOV or
more may be present on the terminal(s).

This stable, low noise high voltage power supply features
front panel digital voltage metering and calibrated direct
reading front panel controls, and a polarity selector
switch. The rear panel features a HV output connector
line power plug, fuse, and a voltage selector switch. The
unit is arc and short circuit protected for safe, reliable op­eration

The WARNING used in this manual explains dangers
that could result in personal injury or death.

The CAUTION used in this manual explains hazards

that could damage the instrument.

l-l

SECTION 1

General Information

1.5 WARRANTY INFORMATION

The warranty is given on the inside front cover of this In­struction Manual. If there is a need to exercise the War­ranty, contact the factory to determine the proper action
to be taken.

NOTE
Attempting to repair or tampering with the
unit while still under warranty (less than 12
months since date of shipment> will void the
warranty. All in-warranty repairs should be
sent to the factory.

l-2

SECTION 2

Operation

2.1 INSTALLATION

WARNING
This unit outputs hazardous voltage that
could cause injury or death. Do not connect
to line power unless ground (GND) and out­put high are properly connected.

Figure 2-l shows the mounting and clearance dimen­sions as well as the controls and connectors on the front
and rear panels. Rubber feet and screws are supplied
with each unit. For benchtop use, remove the four comer
screws and install the four rubber feet using the new
screws.

2.2 FRONT PANEL CONTROLS AND
TERMINALS

Power Switch -A rocker switch turns the line power on

or off to the entire instrument. The rocker switch has a
built-in pilot lamp that is lit when the power switch is on.

Polarity Switch
positive or negative polarity. Also, it switches the output
voltage off.

A two-second delay in the center OFF posi­tion is required when switching polarity.

Voltage Switch - The Voltage switch sets the output

voltage in increments of 500V from OV to 2OOOV.

Voltage Dial - The Voltage dial is a 10 turn digital dial
that supplements the Voltage switch setting by up to
1ooov.

Before turning the power on to the instru­ment, make sure the voltage switch and dial
are properly set. Monitor the output on the
meter when the power is on.

-The polarity switch sets the output for

CAUTION

WARNING

Output Meter -The output meter monitors the output

voltage. Meter operation is independent of the AC input
power; therefore, it reads the output at all times.

NOTE
The output voltage is the sum of the Voltage
dial and the Voltage switch.

2-l

SECTION 2

Operation

2.3 REAR PANEL CONNECTORS AND
TERMINALS

GND -The case ground screw (GND) is to be connected

to the measurement system common.

Output Connector -

type UG931/U connector. It mates with a h4HY type
UG932/U connector.

j

Figure 2-l.

Model 247 Front Panel

The output connector is a h4lW

Fuse -The line power fuse (Slo-Blo) is rated 1.6A, 250V
for 90-127V AC operation and 0.8A, 250V for 180~254V
AC operation.

Line Voltage Selector -

the appropriate line voltage 90-127VAC or MO-254V AC.

Line Plug - The recessed line plug accepts a three-wire
female line plug for line power.

The line voltage selector selects

Figure 2-2.

2-2

Model 247 Rear Panel

SECTTON=!

Opera f ion

2.4 PREPARATION FOR USE

Perform the following procedure to prepare the Model
247 .- tor use:

1.

Set the Model 247 for proper line voltage operation
as specified in paragraph 2.5.

2.

Connect a ground wire from case ground (on rear
panel) to the measuring system common.

3.

Set the front panel controls to:

A. Power switch - OFF

B. Polarity switch - OFF

C. Output voltage switch - 0

D. lOtumdigitaldial- 000 (full counterclockwise)

Plug the line cord into the power line with a three-

4.
wire receptacle to maintain proper case ground.

WARNING
This unit is equipped with a three-wire
grounded line cord. This must be used with a
three-wire receptacle where the “third wire”
is connected to earth ground, otherwise per­sonal injury or death may occur.

5.

Connect the output of the Model 247 to the circuit.
Use a properly rated coaxial cable with the supplied
MHV type UG932/U mating connector to insure

good circuit connections and safe operation. Refer to
paragraph 2.6.

6.

Set the Polarity switch to the desired polarity.

Turn on the power to the instrument. With actual

7.
load and output voltage, allow one hour for warm

UP-

Increase the Voltage switch slowly to reach the ap-

8.
proximate desired voltage. Then trim the voltage
with the Voltage dial until the desired voltage level
is obtained.

WARNING
Always turn power OFF and verify that the
Model 247’s output meter reads OV DC, be­fore connecting or removing any equipment.
External circuits may retain High Voltage af­ter the Model 247 has been turned off. Dis­charge any residual voltage before connect­ing or removing any equipment.

lector switch on the rear panel selects either 90-127V
(11OV setting) or 180~254V (22OV setting) operation.

The line fuse ratings are as follows:

Line

Voltage Fuse Rating

90-127VAC 1.6A, 25OV, slow blow

5x2On-m

180-254VAC O.SA, 25OV, slow blow,

5x2Omm

Keithley
Part No.

FU-96-7

Fu-96-6

2.6 CURRENT LIMITING

The Model 247 includes a current limiting circuit that

automatically drops the output voltage to a safe level
when the rated output current is exceeded by 20%. Refer
to the Maximum Current specification when operating
the unit at reduced output voltages or when operating in

a current limit mode for capacitor charging.

2.7 HIGH VOLTAGE OUTPUT

The high voltage output connector is located on the rear
panel (output LO is connected to chassis). A MHV type
UG932/U shielded mating connector is supplied with

each unit. Assembly insinrctions for the connector are
listed below.

Gently cut through the outer insulation without cut-

1.
ting the shield.
Using a sharp point, unravel the shield braid.

2.
Clean off all traces of graphite.

3.

4.

Cut the center insulation to the proper length cap­proximately 3/8”). Cut the center conductor to ap­protiately l/8”.
Solder center conductor to male pm. Cut the braid

5.
back so it fits around the connector (see Figure 2-3).
Assemble as in Figure 2-3.

6.

2.5 INPUT POWER

The AC input line voltage required to operate the instru­ment is 90-127V or 180~254V. The recessed line voltage se-

WARNING
When the High Voltage Output is not in use,
turn off the power and cover the output con­nector with the supplied cover cap.

2-3

SECTION 2

tance materials may be measured. Flexible materials such

as PVC, rubber or paper may be tested with the Model
6105 Resistivity Adapter as shown.

-1 )t3/32

UG-932RI Ccnn.
Voltage Rating to 5kV

Figwe 2-3. Connector and Cable Assembly

2.8 APPLICATIONS

The following are four examples of typical applications
of theMode 247, related to the low current capabilities of
electrometers and picoammeters.

2.8.1 Application of 247 with
Photomultipliers

The electron-multiplier requires up to 200 volts per stage
and may have 10 to 14 stages. Thus, a totalsupply voltage
up to 3OOOV may be needed. The overall sensitivity or
gain is very responsive to changes in supply voltage. For
this reason the long-term stability of the supply must be
excellent. The specified stability of the Model 247 is valid
after one-hour warm up- Warm up takes one hour with
a&.& load and output voltage.

The Model 247 is especially useful since it is low-noise
and well-regulated, allowing the more sensitive elec­trometer ranges to be used when measuring high quality

insulators. The front panel polarity switch makes it easy

I

to check for non-linearity (polarity sensitivity).

Warning: Chassis of test
firiure must be connected
a safety earth ground.

?igure 2-S. Resisfivity Measuremenf

2.8.3

Application of 247 with Ionization
Chambers

to

Figure 2-4.

2.8.2

Pho fomulfiplier Circuit

Application of 247 to Resistivity
Measurements

To find resistitity of insulating materials, a known volt-
age is applied to a sample of the material. The resulting
current is measured with a picoammeter or electrometer.
With a source voltage of 1000 volts or more, higher resis-

The electrodes must have a bias voltage of several hun­dred volts to enable them to collect ions. This voltage
must be very steady since fluctuations would be capaci­tively coupled to the picoammeter and cause spurious
readings. The excellent line and load stabilities of the
Model 247 easily meet this need,

-------1

Central Electrode

I

Shield Electrode

------

1 Figure 2-6. Ionizdion Chamber Circuif

2-4

Theory of Operation

3.1 FUNCTIONAL DESCRIPTION

Figure 3-1 is a block diagram of the Model 247. The sche­matic diagram is located in Section 5, Replaceable Parts.
When reading through the Theory of Operation for the
Model 247, it will be helpful to refer to the schematic dia-

gram-

SECTION 3

High

Voltage

OUtpUt

H.V.

Isolation

The circuit uses a DC-DC converter which converts low
voltage DC power to a high voltage DC output. This out­put voltage is highly regulated and filtered and can be
varied by the front panel controls. The input to the DC­DC converter is obtained from internal low voltage
power supplies powered by AC line input.

An oscillator determines the high frequency (approxi­mately 2OkHz) at which all amplification high voltage
transformation, rectification and filtering occurs- The
amplification is a function of a control voltage which per­forms the function of control and regulation. A sample of
the output voltage is compared against a reference volt-

age in the sensing circuit- The sensing circuit generates
the control voltage to set and maintain a fixed high volt­age output.

Figure 3-1. High VoZtage Power Supply Block Diagram

3.2 CIRCUIT DESCRIPTION

The AC input line is converted to the B+ (36VDC) supply
and regulated kl2V low voltage power supplies. The B+
supply is a filtered full wave rectifier circuit located on
the chassis. The regulated low voltage power supply cir­cuit (+12VI consists of a rectifier circuit located on Tl and
output regulators located on PCB-100.

The output of the oscillator circuit which is amplified in
the AGC amplifier, is a function of the control voltage de­veloped at the output of the error amplifier.

3-I

SECTION 3

Theory of Operation

The encapsulated high voltage assembly includes a high
voltage transformer, rectifier or multiplier circuits, ripple
filter and sensing circuit. These are all critical custom de­signed and encapsulated components.

A sample of the high voltage DC output is fed to the out­put voltage sensing circuit, and is compared to a com-

mand voltage. Output voltage control is obtained by
varying the command voltage fed to the error amplifier.
The error amplifier compares the command voltage and
the signal from the output voltage sense circuit. Any dif­ferences causes a correction in the gain control of the
AGC amplifier. The command voltage is controlled by
the front panel controls; The reference and reference con­trol and buffer provide a stable -5VDC to the front panel
output voltage controls.

3-2

SECTION 4

Maintenance

4.1 INTRODUCTION

Section 4 contains information required for the mainte­nance of Model 247 units. It is organized around the veri­fication procedure used to determine that the equipment
is operating to specifications.

WARNING

The procedures in this section are for use
only by qualified service personnel. Do not
perform these procedures unless qualified
to do so. Many of the steps in this section
may expose you to potentially lethal volt­ages that could result in personal injury or

Table 41. Recommended Test Equipment

Item

r

Description

A

Oscilloscope

B

Digital Voltmeter

C

Variable Auto Transformer

D

Voltage Divider

E

Load Resistor

P

AC Viewing Circuit

G

Power Line Ammeter

Specifications Manufacturer Model

lOMH2 Phillips

-001% Keithley

1000 to 1 Julie Research

-

.I% Valhalla Scientific 2000

death if normal safety precautions are not
observed.

WARNING

To prevent a shock hazard, remove the line
cord and all test leads from the instrument
before removing any cover.

4.2 RECOMMENDED TEST EQUIPMENT

The recommended test equipment required to test and
maintain the Model 247 is listed in Table 4-1.

3234

192

General Radio

Clarostat

3030-5118

HV-10
VP-50-k-5Ok-50M

4-l

SECTION 4

Maintenance

Potentiometer R178 is an Overload Adjustment. To cali-

HV

0

brate this adjustment set the Model 247 for full load and

I

full voltage (3000V at 6mA) by using the load resistor (E)
on the output. Adjust R178 until the voltage drops off and
then back off of R178 approximately l/8 of a turn.

Potentiometer R173 is a Frequency Adjustment. To cali­brate this adjustment set the Model 247 for full load and
full voltage (3000V at 6mA) by using the load resistor (E)
on the output. Adjust R173 for minimum AC power line
current.

4.3 PREPARATION FOR
MEASUREMENTS

Connect the HIGH VOLTAGE OUTPTJT of the Model
247 to the high voltage terminal of the DC voltage di­vider (D) and to the capacitor input of the AC viewing cir­cuit (F). The low voltage terminal of the DC divider

should be connected to the digital voltmeter input, and

the AC viewing circuit output connected to the oscillo-

scope input. Make sure that a good ground is connected
to all instruments, viewing circuits and the Model 247.
After the ground has been checked, adequate safety pre­cautions have been taken, and the output voltage con­trols set at zero, input power can be applied. The AC in­put should be applied through the variable autotransfor­mer, which should be initially set for 115 or 230 volts out­put, as appropriate.

4.4 CALIBRATION ADJUSTMENTS

WARNING
To prevent a shock hazard, remove the
power cord and all test leads from the Model
247 before removing any cover.

Remove the top cover of the Model 247. Set the Volts
switch to 0. Set the Volts dial to read 1000. Adjust the Ref­erence Adjust Potentiometer (R172) of PCB 100 (see Fig­ure 4-l) for an output voltage of 1000 volts.

Adjustment is not complete. The following performance
tests are used to determine that the unit meets all of its
specifications.

4.5 PERFORMANCE TESTS

Check to assure that the procedures in paragraph 4.3
have been followed.

NOTE
Performance tests may be performed without
doing the calibration.

Turn the front panel output volts control fully clockwise
until the reading on the digital voltmeter indicates maxi­mum output from the Model 247.

Connect one end of the high voltage load resistor to
ground and the other end to a shorting stick (1 ft. insu­lated stick to which the load resistor is attached). Then,
with the shorting stick, connect the load resistor across
the high voltage output and observe the change in output
voltage. During this no load to full load test, the digital
voltmeter reading should not change by more than

0.005%.

With the load connected as above, observe the AC ripple

voltage on the oscilloscope. The ripple should be less
than the specified peak-to-peak ripple under this condi­tion of full load and maximum output voltage.

Set the Volts dial to read 10 (with the Volts switch still at

0). Adjust the Offset Adjust Potentiometer (R171) for an
output voltage of 10 volts. Set all front panel voltage con-

trols for 3000 volt output and readjust the Reference Ad-

just Potentiometer 01172) if necessary.

42

Vary the autotransformer to produce an AC line input
change of +lO% to the power supply, and again observe
the change in digital voltmeter reading. This change
should be less than 0.001%.

SECTION 4

Maintenance

Additional line and load regulation and ripple measure-

ments may be performed at other voltage levels using the

same procedure outlined above. This should not usually
be necessary. Satisfactory test data at maximum output
voltage and the full range of voltage control generally in-

dicate that satisfactory test data will be obtained at all

voltage levels. However, full range testing is performed

at the factory on each unit prior to shipment.

4.6 TROUBLESHOOTING PROCEDURE

A Model 247 High Voltage Power Supply consists of eas­ily replaceable plug-in printed circuit boards, and a main
chassis assembly which includes the high voltage cir­cuitry. The basic troubleshooting procedure consists of
determining which of these assemblies is defective. Re­moval of the top cover provides access to the printed cir­cuit board and high voltage components. The printed cir­cuit board is secured by four screws to the bottom of the
chassis.

No further disassembly is required for troubleshooting
purposes. Make sure all test instruments are grounded,
either to the high voltage connector shield, or directly to
the chassis, prior to the application of input power to the
unit. The following procedures should then be followed.

voltage should be approximately +41VDC. If this voltage
differs by more than lS%, the power transformer, or
PCBlOO is probably defective.

If the B+ supply is operating properly, check for unregu­lated tiOVDC output accessible across C103(+) and
C131(-) on PCBlOO. The + voltages should be of equal
magnitude to within 5% and within the range of 16 to
24VDC. If the magnitude and tracking are not within the
range specified, this circuitry is probably defective.

If all of the low voltage power supplies are operating
properly, turn off input power, insert connector to P303,
turn all voltage controls to zero, follow the PREPARA­TION FOR MEASUREMENTS procedure in paragraph

4.3, and turn the line power back on

If output voltage can be obtained, but the unit does not
properly regulate or the front panel control does not op­erate properly, P,CB 100 is probably defective.

If no output voltage is obtainable, test for AC drive to the
base of transistor Ql or Q2 located on the rear of the unit.
If drive is present, the high voltage assembly or transis­tors are probably defective.

Remove connector/cable from I’303 on PCB300 (see Fig­ure 4-l for location). This leaves only the low voltage B+
and the unregulated +20 volt power supplies operable.
Turn on the AC line power and measure the DC voltage
obtained across R101. (See Figure 4-l for location.) This

It is recommended that the unit be returned to the factory
for the repair of the high voltage assembly. Specify model

number and serialnumber in all correspondence with the

factory.

4-3

SECTION 4

Main fenance

Power
Switch

R171

. . - . -

RI73

R178

R172

y!;z; output

Assembly

\InltanP

SECTION5

Replaceable Parts

5.1 INTRODUCTION

Operational spares to support the Model 247 are avail­able from the factory. It is recommended that common
electronic components (i.e. resistors, capacitors, transis­tors, etc.) be purchased from local electronics distribu­tors. These parts are called out on the schematic diagrams
located on the following pages.

5.2 ORDERING INFORMATION

To place an order or to obtain information concerning re-

placement parts, contact your Keithley representative or
the factory. See inside front cover for addresses. When or­dering, include the following information:

1. Instrument Model Number

2. Instrument Serial Number

3. Parts Description

4. Circuit Description (if applicable)

5. PartNumber

5.3 FACTORY SERVICE

If the instrument is to be returned to the factory for serv­ice, please complete the Service Form which follows this
section, and return it with the instrument.

Table 5-1.

Description

Printed Circuit Card (PCB 100) 109641
Printed Circuit Card (PCB 300) 208329

High Voltage module
Power transformer
Bridge rectifier
HV connector
HV Mating connector
Meter
rower switch
Output Voltage switch assembly
Polarity switch
Rubber bumper

Model 247 Replacement Parts

Part Number

308028
40152
ED1 #l?K 10
UG 931 /U
UG 932/U
309206-l
212JGlB60X03
301317
204737
H.H. Smith #2192

5-1

WI-

-

Service Form

Model No.

Serial No.

Date
Name and Telephone No.
Company

List all control settings, describe problem and check boxes that apply to problem.

Ci Intermittent

m IEEE failure
B Front panel operational

Display or output (check one)
5 Drifts

m Unstable
5 Overload

u Calibration only
0 Data required
(attach any additional sheets as necessary)

Show a block diagram of your measurement system including all instruments connected (whether power is turned on or not).
Also, describe signal source.

u Analog output follows display

m Obvious problem on power-up
u All ranges or functions are bad

a Unable to zero
0 Will not read applied input

a Certificate of calibration required

a Particular range or function bad; specify

Q Batteries and fuses are OK
a Checked all cables

Where is the measurement being performed? (factory, controlled laboratory, out-of-doors, etc.)

What power line voltage is used?

Relative humidity?

Any additional information. (If special modifications have been made by the user, please describe.)

Other?

Ambient temperature?

“F

Test Instrumentation Group
Keithley Instruments, Inc.

28775 Aurora Road
Cleveland, Ohio 44 139

Printed in the U.S.A.