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Model 238 High Current
Source Measure Unit
Service Manual




Contains 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 WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PRO-
VIDED 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, INCIDENT' 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 LIM-
ITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY
PERSON. OR DAMAGE To PROPERTY.




KeithIey Instruments, Inc. l 28775 Aurora Road l Cleveland, OH 44139 l 440-248-0400 l Fax: 44@248-6168 l http:Nwww.keithley.com
BELGIUM: Kelthley Instruments B.V. Bergensesreenweg 709 B-1600 Sint-Pieters-L.eeuw OX363 00 40 Fax: 02/363 00 64
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CHINA: KeithIey Instruments China YunnChenXin Building,Rmm 7M 12YuminRoad, Dewai,Madian* Beijing loo029 8610.62022886 Fax: 861@62UZ2892
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FRANCE: Keitbley Instruments Sad B.P. 60 3, all& dea Grays 91122 Palaiseau Ceder. 01 64 53 20 20 Fax: 01 60 11 77 26
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GERMANY: Keitbley Instruments GmbH Imlsberger Stmsse 65 D-82 l I10 089/84 93
Gemming Fax: 089/X4 93 07-34
l 07-40 l


GREAT BRITAIN: Keithley Instruments Ltd The Minster 58 Portman Road Reading, Berkshire RG30 1EA * 0118-g 57 56 66 Fax: 0118-9 59 64 69
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INDIA: Keithley Instruments GmbH Flat 2B, WILOCRISSA 14. Rest House Crescent Bangalore 560 001 91-80-509- 1320/21 Fax: 91-80-509-1322
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ITALY: KeithIey Instruments ~1. Viale S. Gimignano, 38 20146 Milano -02148 u) 30 08 Fax: 02/48 30 22 74
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NETHERLANDS: Keithley Instruments B.V. Postbus 559 * 4200 AN Gorinchem 0183-635333 Fax: 0183-630821
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SWITZERLAND: Keitbiey Instruments SA Kriesbachsaasse 4 8M)o Dtibendorf 01-82 I 94 44 Fax: 01-820 30 8 I
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TAIWAN: Keithley Instruments Taiwan I Fl. 85 POAi Street Hsinchu, Taiwan, R.O.C. 8863572-9077 Fax: 886-3572-903
10199
l l l
Model 238 High Current Source Measure Unit
Service Manual




01990, Keithley instruments, Inc.
Test Instrument Group
All rights reserved.
Cleveland, Ohio, U.S.A.
Third Printing, May 2000
Document Number: 238-902-01 Rev. C
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 B (Document Number 238-902-01) .................................................. August 1992
Revision C (Document Number 238-902-01) ...................................................... May 2000




All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.
Other brand and product names are trademarks or registered trade.marks of their respective holders.
Safety Precautions

The following safety precautions should be observed before using Users of this product must be protected from electric shock at all
this product and any associated instrumentation. Although some in- times. The responsible body must ensure that users are prevented
struments and accessories would normally be used with non-haz- access and/or insulated from every connection point. In some cases,
ardous voltages, there are situations where hazardous conditions connections must be exposed to potential human contact. Product
may be present. users in these circumstances must be trained to protect themselves
from the risk of electric shock. If the circuit is capable of operating
This product is intended for use by qualified personnel who recog- at or above 1000 volts, no conductive part of the circuit may be
nize shock hazards and are familiar with the safety precautions re- exposed.
quired to avoid possible injury. Read the operating information
carefully before using the product. As described in the International Electrotechnical Commission
@EC) Standard IEC 664, digital multimeter measuring circuits
The types of product users are:
(e.g., Keithley Models 175A. 199,2000,2001,2002. and 2010) are
Responsible body is the individual or group responsible for the use Installation Category II. All other instruments' signal terminals are
and maintenance of equipment, for ensuring that the equipment is Installation Category I and must not be connected to mains.
operated within its specifications and operating limits, and for en-
suring that operators are adequately trained. Do not connect switching cards directly to unlimited power circuits.
They are intended to be used with impedance limited sources.
Operators use the product for its intended function. They must be
NEVER connect switching cards directly to AC mains. When con-
trained in electrical safety procedures and proper use of the instru-
necting sources to switching cards, install protective devices to lim-
ment. They must be protect&J from electric shock and contact with
it fault current and voltage to the card.
hazardous live circuits.
Before operating an instrument, make sure the line cord is connect-
Maintenance personnel perform routine procedures on the product
ed to a properly grounded power receptacle. Inspect the connecting
to keep it operating, for example, setting the line voltage or replac-
cables, test leads, and jumpers for possible wear, cracks, or breaks
ing consumable materials. Maintenance procedures are described in
before each use.
the manual. The procedures explicitly state if the operator may per-
form them. Otherwise, they should be performed only by service
For maximum safety, do not touch the product, test cables, or any
personnel. other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
Service personnel are trained to work on live circuits, and perform any capacitors before: connecting or disconnecting cables orjump-
safe installations and repairs of products. Only properly trained ser- ers, installing or removing switching cards, or making internal
vice personnel may perform installation and service procedures.
changes, such as installing or removing jumpers.

Exercise extreme caution when a shock hazard is present. Lethal Do not touch any object that could provide a current path to the
voltage may be present on cable connectorjacks or test fixtures. The common side of the circuit under test or power line (earth) ground.
American National Standards Institute (ANSI) states that a shock Always make measurements with dry hands while standing on a
hazard exists when voltage levels greater than 30V RMS, 42.4V dry, insulated surface capable of withstanding the voltage being
peak, or 60VDC are present. A good safety practice is to expect measured.
that hazardous voltage is present in any unknown circuit before
measuring.
The instrument and accessories must be used in accordance with its The WARNING heading in a manual explains dangers that might
specifications and operating instructions or the safety of the equip result in personal injury or death. Always read the associated infor-
ment may be impaired. mation very carefully before performing the indicated procedure.

Do not exceed the maximum signal levels of the instruments and ac- The CAUTION heading in a manual explains hazards that could
cessories, as defined in the specifications and operating informa- damage the instrument. Such damage may invalidate the warranty.
tion, and as shown on the instrument or test fixture panels, or
switching card. Instrumentation and accessories shall not be connected to humans.

When fuses are used in a product, replace with same type and rating Before performing any maintenance, disconnect the line cord and
for continued protection against fire hazard. all test cables.

To maintain protection from electric shock and lire. replacement
Chassis connections must only be used as shield connections for
components in mains circuits, including the power transformer, test
measuring circuits, NOT as safety earth ground connections.
leads, and input jacks, must be purchased from Keithley Instru-
ments. Standard fuses, with applicable national safety approvals,
If you are using a test fixture, keep the lid closed while power is ap-
may be used if the rating and type are the same. Other components
plied to the device under test. Safe operation requires the use of a
that are not safety related may be purchased from other suppliers as
lid interlock.
long as they are equivalent to the original component. (Note that se-
lected parts should be purchased only through Keithley Instruments
Ifa@ screw is present, connect it to safety earth ground using the
to maintain accuracy and functionality of the product.) If you are
wire recommended in the user documentation.
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.
The A ! symbol on an instrument indicates that the user should re-
fer to the operating instructions located in the manual.
To clean an instrument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
The m symbol on an instrument shows that it can source or mea-
cleaner directly to the instrument or allow liquids to enter or spill
sure 1000 volts or more, including the combined effect of normal
on the instrument. Products that consist of a circuit board with no
and common mode voltages. Use standard safety precautions to
case or chassis (e.g., data acquisition board for installation into a
avoid personal contact with these voltages.
computer) should never require cleaning if handled according to in-
structions. If the board becomes contaminated and operation is af-
fected, the board should be returned to the factory for proper
cleaning/servicing.




Rev. 10199
Model 238 Source Measure Unit Specifications
SOURCE-MEASURE UNIT: Sources voltage while measuring current, or VOLTAGE
sources current while measuring voltage. SOURCE V MEASURE V
FUNCTION: Can be used as DC source or meter, sweep source, or full RANGE ACCURACY ACCURACY'
source-measure unit. (Max. STEP (1 Year, RESOLUTION (1 Year,
SOURCE-DELAY-MEASURE CYCLE: Value) SIZE 18=-WC) 4-Diait S-Diait w-28