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SERVICE MANUAL
Digital Multimeter
Model 178
@ COPYRIGHT 1978, KElTHLEY INSTRUMENTS, INC.
FIRST PRINTING, FEBRUARY 1978, CLEVELAND, OHIO, U. S. A.
SECOND PRINTING, FEBRUARY 1979, CLEVELAND, OHIO, U. S. A.
DOCUMENTSNO. i8970
\
INSTRUCTION MANUAL
olgltal Multimeter
Model 178
CONTENTS
Section Page
CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
ILLUSTRATIONS i ii
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
I. GENERAL INFORMATION 1-l
l-l. INTRODUCTION . . . , . . . . . . , . . . . . . . . . . . . . . , . . . . i-i
l-2. WARRANTY INFORMATION l-l
l-3. CHANGE NOTICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-I
2. OPERATION 2-l
2-l. GENERAL . . . . . . . . . . . . . . . . . , . . , . . . . . . . . . . . 2-1
2-2. INSPECTION 2-I
2-3. PREPARATION FOR USE . . . . , . . . . . . . . . . . . . . . . . . . . . 2-l
2-4. OPERATION ON LINE POWER 2-l
2-5. OPERATION ON BATTERY PACK POWER . . . , , , . . . , . . . . . . . . , . 2-2
2-6. BATTERY CHARGING 2-2
2-7. OPERATING INSTRUCTIONS . . , . . . . , . . . . . , . . . . . . . . . . . 2-3
2-8. DC VOLTAGE MEASUREMENT 2-4
2-9. AC VOLTAGE MEASUREMENT , , . . , . . , . . . . . . . , . . . . , . . . . 2-5
2-10. RESISTANCE (n) MEASUREMENT 2-5
2-11. ZERO ADJUSTMENT . . . , . . . . . . . . . . . . . . . . . , . . . . , . 2-5
2-12. ACCESSORIES 2-5
3. PERFORMANCE VERIFICATION . . . . . . , . . , . . . . . . , . , . . . . . . . . 3-1
3-l. GENERAL 3-l
3-2. RECOMMENDED TEST EQUIPMENT . . , . . . . . . . . . . . . . . . . . . . . 3..1
3-3. ENVIRONMENTAL CONDITIONS 3-l
3-4. PERFORMANCE VERIFICATION PROCEDURE . . , . . . . . . . . . . . . , . . . 3-l
4, CALIBRATION 4-l
4-1. GENERAL .,,..........,.............,....4-I
4-2. RECOMMENDED TEST EQUIPMENT 4-l
4-3. ENVIRONMENTAL CONDITIONS . . . . . . . . . . . . . . , . . , , , . , . , 4-l
4-4. CALIBRATION PROCEDURES 4,-l
5. TROUBLESHOOTING . . . . . . , . . . . . . . . . . . 0 . . . . . . . . . . . . 5-l
5-l. GENERAL 5-I
5-2. TROUBLESHOOTING PROCEDURE . . . . . . . . . . . . . . . . , , . . . . . 5-1
6. THEORY OF OPERATION 6-1
6-1. GENERAL , .
O"ERALL O;ERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-l
6-i
6-2.
6-3.
6-4. ATTENUATION
AC CON"ERSION. . . . . . . . . . . . . . . . . . . . * . . . . . . . . . 6-3
6-4
6-5. OHMS CONVERSION . . . . . . . . . . . . . . . . . . . , . . . . . . . . 6-5
6-6. A/D CONVERTER 6-5
6-7. DISPLAY .,................,.........6-6
6-8. AC POWER &J;P;Y' ' 6-6
6-9. MODEL 1788 BATTERY PACK , , . . . . . . , . . . . . . . . . . . . . . . 6-6
7. REPLACEABLE PARTS 7-l
7-l. GENERAL . . . . . . . . . . . . . . , . . . . . . . . . . . . . , . . . 7-l
7-2. ORDERING INFORMATION 7-l
7-3. MAINTENANCE KIT . . . . . . . . . . . . . . , . . . . . . . . , . . , . 7-1
AA
INSTRUCTION MANUAL
Digital Multlmatar
Made1178
CONTENTS (Cont'd)
Section Page
J-4. FACTORY SERVICE . . . . . , . . , . . . . . . . . . . . . . , . . . . . 7-2
7-5. SCHEMATIC 7-2
J-6. COMPONENT LAYOUT . . . . . . . . . . . , . . . . . . . . . . . . . . . , 7-2
ILLUSTRATIONS
Figure No. Title Page
l-l. Front Panel . . . . . . . . . . . . . . . . . . . . . . . ...**. l-l
l-2. Dimensional Data l-2
l-3. Tilt Bail Positions . . . . . . . , . . . . . . . , . . . . . . . . . l-3
Z-l. Rear View Showing Line Switch 2-1
2-2. Battery Pack installation . . . . . . . . . . . . . . . . . . . . . , 2-3
2-3. Operating Controls 2-4
2-4. Model 1600 High Voltage Probe , , . . . . . . . . . . . . . , . . . . 2-6
2-5. Accessories 2-7
2-6. Model 1682 RF Probe and Model 1685 Clamp-On AC Current Probe . . . . . 2-J
2-J. Carrying Case and Rack Mounting Kits 2-8
Integrator and Comparator Waveforms . . . . . . . . . . . . . . . . . 5-4
;:I* Signal Flow Block Diagram, Model 178 DMH b-l
6-2: Attenuation and Ohms Conversion . . . . . . . . . . . . . . . 6-2
6-3. A/D Converter Function (Sheet I o; ;)' ' 6-7
b-3. A/D Converter Function (Sheet 2 of 2) . . . . . , . . . . . . . . . . 6-8
7-l. Schematic Diagram Model 178 Digit Multimeter J-10
Component Layout, PC-447 . . . . . . . . . . . . . . . . . . . . . . . 7-11
;:;: Component Layout, PC-449 7-12
J-4. Component Layout, PC-451 . . . . . . . . , . . . . . . . . . . . . . . 7-13
AA iii
INSTRUCTION MANUAL
DIgItal Multlm.trr
Model 178
SPECIFICATIONS
4C VOLTAGE
ACCURACY 112 months, TEMPERATURE COEFFICIENT
(above 2000 CO"",.l O%lR~ an.4 kw~-550C
. _. _ _ _
MAXIMVM 18~-28~C: 100 HZ-lOkHZ +,x `dg + dmt,
~~~.~.Jl/OC
RANGE READING ,(% rdp + digits) 4SHZ-lOkHZ IOk"z-ZOkHz
2v 19999 0.4% + 153 0.04% + O.Sd 0.09% + O.Sd
20 v 19~999 0~3% + 15d nn,s+n!% " _ I
_. _ _ 0.03% + 0.53
200 v 199.99 0.3% + t Ed 0.01%+0.% 0 "3% + &5d
_._-. _~._
1000" 1000.0 0.3% + 1 Sd 0.01% t 0.5d 0.03% + 0.53
3ESISTANCE
ACCVRACY 112 manthd TEMPERATURE COEPPlClSNT
MAXIMUM W-28% oo-180 and 28%35% NOMINAL
IANGE READING Lf% rdg + digit4 +(% rdp + digits)/% APPLIED CVRRENT
2kO 1.9999 0.04% + 26 0.003% + 0.2 IrnA
20kR 0.04% + Id 0.003% + 0.2 1ooll A
200 kll I %%: 0.04% + ld 0.003% + 0.w lOLlA
`000 kR 1999.9 0.04% + Id 0.003% + 0.2d 1il A
20MR 19.999 0.10% + Id 0.02 x + 0.2d 0 ,PA
AA v
WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of I year from date of
shipment.
Keithley Instmments, Inc. warrants the following items for 90 days from the date of shipment: probes. cables. rechargeable batteries.
diskettes, and documentation.
&ring 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 wrll
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. transpottation prepaid. Rep&red or replaced products il~e warranted for the balance of the ori_ei-
nal 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. 01
problems arising from normal wear or failure to follow instructions.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY LhlPLIED
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A P&RTICULAR 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 KBITHLEY INSTRUMENTS, n\rC.. 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 SUS%4UiED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY
GENERAL INFORMATION INSTRUCTION MANUAL
Digital Multimeter
Model 178
POLARITY (NEGATIVE IS INDICATED, POSITIVE IS IMPLIED
WHEN MINUS (-) DISPLAY IS OFF)
\
FUNdTlON RA'NGE I
/ PUSHBUTTONS PUSHBUTTONS ZERO
POWER \ ADJUST
TILT BAIL
FIGURE I-I. Front Panel.
1-o AA
INSTRUCTION MANUAL GENERAL INFORMATION
DIsItaI Multlmatrr
Model 178
SECTION I. GENERAL INFORMATION
I-I. INTRODUCTION, The Model I78 DMM is a versatile digital multimeter useful for
measurement of both ac and dc voltages as well as resistance. Ranges and accuracies
are listed in the table of specifications on Page v. Ranges and functions are selected
with pushbuttons on the front of the unit. The Model 178 automatically indicates
polarity and positions the decimal point.
I-2. 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 Keithley
Representative in your area to determine the proper action to be taken. Keithley nain-
tains service facilities in the United Kingdom and West Germany, as well as in the
United States. Check the inside front cover of this Instruction Manual for addresses.
l-3. CHANGE NOTICES. Improvements or changes to the instrument which occur after
printing of the Instruction Manual will be explained on a Change Notice sheet attached
to the inside back cover.
I NPORTANT
The A symbol can be found in various places in this Instruction Manual. CarefzJl ly
read the associated CAUTION statements with regard to proper use and handling
of the instrument. Damage to the instrument may occur if these precautions are
ignored.
\
The \ symbol can be found in various places in this Instruction Manual. This
symbol indicates those areas on the instrument which are potential shock hazards
Carefully read the associated WARNING statements with regard to proper use and
handling of the instrument. Serious personal injury may result if these pre-
cautions are ignored.
FIGURE l-1. Front Panel
AA I-1
GENERAL INFORMATION INSTRUCTION MANUAL
Digltal Mullimeter
Modal 178
235 J
(9-114)
DIMENSIONS IN MILLIMETERS (INCHES)
FIGURE l-2. Dimensional Data
l-2 AA
INSTRUCTION MANUAL GENERAL INFORMATION
Dlghl MultImeter
Model 178
J==s+
LEVEL POSITION - TILTBAIL AT FRONT
HANGING POSITION
J
& 45" POSITION s-C6
LEVEL POSITION - TILTBAIL AT REAR
FIGURE l-3. Tilt Bail Positions.
AA l-3
INSTRUCTION MANUAL OPERATING INSTRUCTIONS
DIgItal MultImeter
Model 178
SECTION 2. OPERATION
2-l. GENERAL. This section provides information needed for incoming inspection and
preparation for use.
2-2. INSPECTION. The Model 178 was carefully inspected both mechanically and electric-
ally before shipment. Upon receiving the instrument, check for any obvious damage xnich
may have occurred during transit. Report any damages to the shipping agent. To ,veriFy
the electrical specifications, follow the procedures given in Section 3.
2-3. PREPARATION FOR USE. The Model 178 is shipped ready-to-use. The instrument nay
be powered from line voltage or from rechargeable batteries (when the optional Model I788
Rechargeable Battery Set is installed).
2-4. OPERATION ON LINE POWER. The Model 178 is provided with a.three-wire line tori!
which mates with third-wire grounded receptacles. Connect the instrument to ac line
power as follows:
CAUTION
Connect only to the line voltage selected. Application of incorrect
A voltage can damage the instrument.
a. Set the LINE VOLTAGE switch on the back of the instrument to correspond to the
line voltage available. Ranges are 105 to 125 volts ac and 210 to 250 volts ac as
shown in Figure 2-I.
WARNING
Ground the instrument through a properly grounded receptacle before
operation. Failure to ground the instrument can result in severe
t injury or death in the event of short circuit or malfunction.
b. Plug the power cord into a properly grounded outlet. Operate the 178 DMM as
described in Section 2-7.
This adjustment is used only for
calibration. It is not intended for
adjustment during operation.
FIGURE 2-l. Rear View Showing Line Switch
AA 2-l
OPERATING INSTRUCTIONS INSTRUCTION MANUAL
Digital MultImeter
Model178
2-5. OPERATION ON BATTERY PACK POWER. The Model I78 DMM may also be operated from
rechargeable sealed lead-acid batteries contained in the optional Model 1788 Battery
Pack. The pack will operate the 178 DMM for up to 6 hours. Circuits within the battery
pack will automatically shut down the instrument when the battery charge is insufficient
to maintain accurate readings. Refer to Figure 2-l and install the battery pack as
follows:
WARNI NG
Disconnect the line cord before removing the case cover.
t
a. Turn off the power and disconnect the !ine cord. Remove four screws from the
bottom of the case and separate the top cover from the bottom cover.
b. Lift off the calibration shield, and save it for later use. The Four plastic
spacers must remain in place on the upright studs projecting through the ma in circuit
boa rd.
NOTE
Do not discard the calibration shield. This shield must be installed during
calibration as described in Section 4.
c. Set the BAT/LINE switch to the BAT position shown in Figure 2-2. Note that the
battery pack will not operate properly if this switch is not in the BAT position.
d. Remove fuse F301 on the battery pack.
e. Install the battery pack in the instrument so that it rests on the plastic spacers.
The ground clip must make contact with the upper side of the battery pack plate.
f. Carefully align the battery pack plug with connector PI004 on the circuit board.
Push the plug firmly onto the connector until the lip on the plug engages the lip on the
connector to lock the plug in place.
CAUTION
Make sure the connector is aligned so that all pins mate properly, other-
wise, damage to the DMM will result.
9. Install fuse F301. Reinstall top cover and secure with four screws.
h. Charge the battery pack as described in Paragraph 2-6.
2-6. BATTERY CHARGING. The Model 1788 Battery Pack contains an integral battery charger.
To charge or recharge the battery pack, install the battery pack in the 178 DMM as de-
scribed above and proceed as follows:
a. Connect the instrument to line power as described in Paragraph 2-4.
b. With the power switch off, the battery charge circuitry is automatically energized
to charge the battery at the maximum rate. When the battery pack is first installed, or
if it has completely discharged, allow it to charge for at least 14 hours in this
condition.
NOTE
For maximum battery life, do not allow the battery pack to remain completely
discharged. Constant charging will not harm either the battery pack or the
instrument.
2-2 AA
INSTRUCTION MANUAL OPERATING INSTRUCTIONS
Dlgltel Multlm*ter
Model 178
a BATTERY FUSE F301
LINE FUSE FlOl \\--\
GROUND CLIP
:7
CONNEC
PLASTIC SPA&
(4 PLACES)
FIGURE 2-2. Battery Pack Installatlo".
c. When the 178 DMM is in use on line power, the battery charger maintains a trickle
charge on the battery peck.
2-7. OPERATING INSTRUCTIONS. Refer to Figure 2-3 and operate the OMH as follows:
a. Turn on the power by depressing the ON/OFF pushbutton.
b. Select the function with the DCV, ACV or fl pushbutton.
C. Select the range by depressing the appropriate pushbutton. For ac and dc voltage
measurements there are four ranges available. For resistance measurements there are
five ranges. The pushbuttons are interlocked to avoid improper settings.
d. Connect the source to the INPUT terminals.
AA 2-3
OPERATING INSTRUCTIONS INSTRUCTION MANUAL
DIgital Multimeter
Model 178
P0LARlT.Y (NEGATIVE IS INDICATED, POSITIVE IS IMPLIED WHEN MINUS I-) DISPLAY IS OFF1
1~
. / /
SET POWER ON SELECT FUNCTION SELECT RANGE
"ADJUST ZERO AS REQUIRED FOR MEASUREMENT OF DC VOLTAGE AND RESISTANCE. SEE SEC. 2-11.
FIGURE 2-3. Operating Controls.
CAUTION
MAXIMUM RATINGS: A
DCV :~ (2V): 450V rrns continuous; 1200V peak, for 8 seconds per minute.
(20-IZOOV): l2OOV peak.
ACV: (All Ranges): IOOOV rms;
, IO'V.Hz.
fl: (All Ranges): 250V rms sine wave or 350V peak.
e. Accessories described in Paragraph 2-12 should be used as required.
2-a. DC VOLTAGE MEASUREMENT. Use the Model 178 DMM to measure dc volts as follows:
a. Turn on power and depress the DCV pushbutton.
Select the desired range from the four ranges available. The maximum reading is
Overrange is indicated by a flashing 0000 except on the IOOO-volt range.
CAUTION
n ! Do not exceed the maximum ratings, Instrument damage may occur.
Negative polarity is displayed automatically. Positive polarity is implied when
thz'minus (-) display is off.
d. Zero the instrument as described in Paragraph Z-II before the first use, whenever
the instrument is used outside the temperature rahge of 18" to 28'C, and approximately
weekly during normal use.
2-4
AA
INSTRUCTION MANUAL OPERATING INSTRUCTIONS
Dlgiml Multlmstor
Model 178
2-y. AC VOLTAGE MEASUREMENT. Use the Model 178 DMM to measure ac volts as follows:
a. Turn on power and depress the ACV pushbutton.
CAUTION
I Do not exceed the maximum ratings. Instrument damage may occur.
L!J
b. Select the desired range from the four ranges available. The maximum reading is
19999. Overrange is indicated by a flashing 0000 except on the IOOO-volt range. The
instrument reads the root mean square value of a sine wave with a frequency of 45 to 20
kHz.
c. The Model 1682 RF Probe (see Paragraph Z-12e) should be used to measure ac ,ioltaqes
with a frequency of 20kHz to IOOMHz.
Z-10. RESISTANCE (0) MEASUREMENT. Use the 178 DMM to measure resistance as follo:./s:
a. Turn on power and depress the SI pushbutton.
CAUTION
A 1 Do not exceed the maximum ratings. Instrument damage may occur.
Select the desired range from the five ranges available. The maximum readinq is
I Yk9. Overrange is indicated by a Flashing 0000. The letter k refers to kilohms, and
M refers to megohms.
c. The HI input terminal is positive and causes Forward conduction of semiconductor
junctions.
d. Two volts is applied at full range with 5 volts maximum under open circuit conditions.
Zero the instrument as described in Paragraph Z-II before the First use whenever
thz'instrument is used outside the temperature range of 18" to 28"~, and appr;ximarely
weekly during normal use.
Z-11. ZERO ADJUSTMENT. The zero adjustment nulls input offset on the 20, 200 and 1200
volt ranges and on all resistance ranges. Typically, this adjustment need not be per-
formed more often than once a week unless the instrument is operated at ambient
temperatures outside the range of 18" to 28◦ Jabse Service Manual Search 2024 ◦ Jabse Pravopis ◦ onTap.bg ◦ Other service manual resources online : Fixya ◦ eServiceinfo