HP 421A Service manual

,
НР 427A
SM: 94)— opp YP
OPERATING AND SERVICE MANUAL
PROPERTY OF
ELECTRICAL ENGINEERING
VANDERBILT UNNER SITY VOLTMETER
421A
HEWLETT Åp; PACKARD
Vilt dH

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OPERATING AND SERVICE MANUAL
-hp- Part No. 00427-90004
MODEL 427A
VOLTMETER
Serials Prefixed: 947-
Appendix C, Manual Backdating Changes,
С % adapts manual to serials prefixed 550-, 621-, 731-
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Copyright Hewlett-Packard Company 1969
P.O. Box 301, Loveland, Colorado, 80537 U.S.A.
Printed: JAN 1970

a a
e
e
Table of Contents
TABLE OF CONTENTS
Model 427A
Section Page
I GENERAL INFORMATION . . ...... 1-1
1-1. Description. ......... .. 1-1
1-5. Вайегу.............. 1-1
1-7. Instrument and Manual
Identification. . . ....... 1-1
1-10. Available Accessories ...... 1-1
1-12. Cables and Adapters ..... 1-1
1-13. Probes, “22524 04 asa a Jal
Section Page
п INSTALLATION ............. 25-1
2-1. Introduction. ........... 2-1
2-3 Initial Inspection . . . . . 557221
2-9. Power Requirements, . . . . . , 2-1
2-7. Grounding Requirements. . ... 2-1
2-10. Installation. ........... 2-1
2-12, Bench Mounting ........ 2-1
2-14. Rack Mounting. ........ 2-1
2-16. Combination Mounting .... 2-1
2-18. Repackaging for Shipment .... 2-1
Section Page
ІП OPERATING INSTRUCTIONS ...... 3-1
3-1. Introduction. ........... 3-1
3-3. Front and Rear Panel
Description .........
Operating Instructions ,....
Mechanical Zero Adjustment
Turn-On Procedure. . . . .
1 DC Measurements. ,....
2. Resistance Measurements
3. AC Measurements. .... А
6
Section
IV THEORY OF ОРЕБВАТІОМ,......
4-1. General. ............
4-5. DC Орегаһоп..........
Ohms Operation ........
. AC Operation. .........
2.
Circuit
Descriptions,
.....
3. DC Amplifier (A1). . . .,.
6. DC Offset (А2) ... .
9. AC Metering Circuit (A2) ния
3. Battery Regulator Al....
Section
У MAINTENANCE ............
5-1, Introduction ..........
9-3. Required Equipment ,......
5-5. Performance Checks
DB Measurements. ,.....
.
У ФА) Q3 C2 Q3 023 2 C3 CO
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Section
У MAINTENANCE (Сопе' 4)
9-7. АС Accuracy and Frequency
Page
Response Check. .... 5-1
5-14. Resistance 2. Check. 5-2
5-16, DC Accuracy. 4 4.50...» 5-2
5-18. AC Rejection Check . sé aaa des
5-20. Input Impedance Check .... 5-3
5-25. Adjustment and Calibration
LIST OF TABLES
Number Page
1-1. Specifications ..,............. 1-0
3-1. Effects of Harmonic Distortion. . . . . 3-2
3-2. DB Range Identification. . . . . .. .. 3-2
5-1. Required Test Equipment, ....... 5-0
5-2. Resistance Accuracy Check. . . . . . . 5-2
01791-2
Procedures ......... . 5-4
5-21. Cover Removal ........ 5-4
5-30. Amplifier Balance and Zero
Offset Adjustment. . . . . . 5-5
5-31. Regulator Adjust ....... 5-5
5-32. AC Calibration. ........ 5-5
5-36, Resistance Infinity Adjustment 5-6
5-38. DC Calibration. ........ 5-6
9-40. Alternate Performance Checks
and Calibration Procedures. . 5-6
5-42. AC Сїтсїв.......... 5-6
5-45. Resistance Circuits. . . . .. 5-6
5-47, DC Circuitfs 32,22 xxx 5-7
5-50. АС Rejection ......... 5-7
5-52. Input Impedance Check .... 5-7
5-54. Battery Replacement. . . .... 5-7
5-56. Troubleshooting. ......... 5-7
5-60. Power Supply ......... 5-8
5-63. DC Amplifier ......... 5-8
5-67. AC Metering Circuit, ..... 5-8
5-71. Adjustment of Factory Selected
Components ...... .... 5-8
5-13. MRI 1.15114. xw ca кез 5-8
5-75. A2C2* så xg Xov 5-9
5-77. A2R14* T . 5-9
5-80. A2R16* ..... 4-8 ызык va 10-9
5-82. Etched Circuit Board Repair. 5-9
Section Page
VI CIRCUIT ПЛАСВАМ$.,,....... 2. 6-1
6-1, Introduction ............ 6-1
Section Page
ҮП REPLACEABLE PARTS.......... 7-1
1-1. Introduction ............ 7-1
7-4. Ordering Information. . . . . . . . 7-1
7-6. Non-Listed Parts. . . ... века 41-1
Appendix
А CODE LIST OF MANUFACTURERS
B SALES AND SERVICE OFFICES
С MANUAL BACKDATING CHANGES
Number Page
5-3. 1% Resistors............ Ux. 5-7
5-4. Troubleshooting. .......... .. 5-7
5-5. Power Supply Voltages ,........ 5-8
5-6 AC Metering Circuit Voltages ..... 5-8
7-1. Replaceable Parts. .. ......... 7-1
iii

Table of Contents
Model
427A
Voltmeter
, .
.
11096A
High
Frequency
Probe.
.
Location
of
Front
Panel
Controls
and
Indicators.
.
.
Impedance
Correction
Graph
Simplified
Block
Diagram
.
.
DC
ОрегаПоп.........
Ohms
Operation
.......
AC
Operation
DC
Offset
Circuit,
,.
» .
+
+=
AC
Accuracy
and
Frequency
Response
Check.
.
.
.
Моде! 427А
OF
ILLUSTRATIONS
Page
Number
Page
.
1-0
5-9,
Resistance
Accuracy
Сһеск.......
5-2
‚
1-1
5.3.
DC
Accuracy
and
Linearity
Check.
...
5-2
5-4,
AC
Rejection
Сһеск...........
5-3
.
3-0
5-5,
Input
Impedance
Check
.........
5-4
.
3-3
5-6.
Location
of
Internal
Adjustments
....
5-5
.
4-0
5-7,
Battery
Керісетепі...........
5-7
. 4-1
.
4-2
6-1.
Location
of
Switch
Components
....
-
6-2
.
4-2
6-2.
Component
Госапоп,..........
6-3
4-3
6-3.
Schematic
Diagram
...........
6-3
.
5-0
1-1.
Location
of
Mechanical
Рагів......
7-0
01791-2
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Section
I
Model
427A
в
a ын
| |
ҮМЕТЕН
HEWLETT
·
PACKARD
@
4274
VOLI
» FUNCTION
3
EEE
Figure
1-1.
Model
427A
Voltmeter
Table
1-1.
Specifications
DC VOLTMETER
Voltage
Ranges:
+100
mV
to
+1000
У
full
scale
па
1,
3,
10
sequence
(9
ranges).
AC
VOLTMETER
(Cont'd)
==
а
bl
си
ОПТ
а)
Input
Impedance;
10
megohms
shunted
by
40pF
on
10
mV
to
1
V
ranges;
20
pf
on
3
V
to
300
V
ranges.
Response:
Responds
to
the
average
value
of
the
in-
put;
calibrated
in
rms
voltsfor
а
sine
wave
input.
Overload:
300
V/rms
momentarily,
1
V
range
and
Accuracy:
+2%
of
full
scale
on
any
range
(09C
to
50°C),
Input
Resistance:
10
megohms
on
all
ranges.
Ре
у
below
AC
Rejection:
Superimposed
peak
ac
voltages
(60
M
:
Hz
and
above)
100
times
greater
than
full
scale
425
V/rms
maximum
above
1
V
range.
affects
reading
less
than
1%.
Maximum
450
OHMMETER
volts peak.
Overload:
1200
Vdc
on
any
range.
AC VOLTMETER
Voltage
Ranges:
10
mV
to
300
V
rms
full
scale
in
a
1,
3,
10
sequence
(10
ranges).
Frequency
Range:
10
Hz
to
1
MHz.
Accuracy:
(0°C
to
50°C),
RANGE
+2%
OF
FULL
SCALE
0.01
V
-
30
V
10
Hz
-
1
МН?
100
V
-
300
V
10
Hz
-
100
KHz
Frequency Response:
Resistance
Ranges:
10
ohms
center
scale
to
10
meg-
ohms
center
scale
(7
ranges).
Accuracy:
+5%
of
reading
at
midscale
(00C
to
+50°C),
Polarity:
Common
terminal
negative,
source Current:
OPEN
CIRCUIT
|
SHORT
CIRCUIT
RANGE
VOLTAGE
CURRENT
X10
3d8
edB
IdB
О
GENERAL
Floating
Input:
May
be
operated
up
to
500
Vdc
above
ground.
(Ohms
input
open
in
any
function
except
ohms--volts
input
open
when
instrument
is
in
off
position.)
Power:
22-1/2
volt
dry
cell
battery.
(Eveready
No.
763
ог
RCA
VS102.)
Option
01:
Battery
operation
and
ac
line
opera-
tion
(selectable
on
rear
panel).
115
or
230
V
+20%,
50
Hz
to
400Н2,
1/2
W.
IHz
SHz
lOHz
IMHz
eMHz 3MHz
4MHz
Frequency
response
10
mV
to 30
V
ranges,
1-0
01791-2
44

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Model 427A
Section I
SECTION 1
GENERAL
1-1. DESCRIPTION.
1-2. The Hewlett-Packard Model 427A is a versatile,
compact, self-contained voltmeter. It is capable of
making de measurements from 1 mV to 1000 volts, ac
measurements from 0. 3 туѓо 300 volts at frequencies
from 10 Hz to 1 MHz, and resistance measurements
from 0.2 ohms to 500 megohms. With the 01 option,
the Model 427A may be powered either by a 115 or
230 volt line or by an internal 22-1/2 volt dry cell
battery.
1-3, The use of solid state components throughout
gives the Model 427A both ruggedness and reliability,
Battery operation makesthe instrument ideal for field
use or isolation from common mode ground loops.
1-4, Figure 1-1showsthe Model427A, and Table 1-1
contains а list of the Model 427A Specifications,
1-5. BATTERY.
1-6. The battery used in the Model 427A is a 22-1/2
volt dry cell, Eveready No. 763 or an RCA VS102.
Typical battery life is morethan 300 hours continuous
operation or 700 hours intermittent operation.
1-7. INSTRUMENT AND MANUAL
IDENTIFICATION.
1-8. Hewlett-Packard uses a two-section eight-digit
serial number (000-00000). If the first three digits
(prefix) of the serial number on your instrument do
not agree with those on the title page of this manual,
INFORMATION
change sheets supplied with the manual will define
differences between your instrument and the Model
427A described in this manual.
1-9. If a letter prefixes the serial number, the
instrument was manufactured outside the United
States.
1-10. AVAILABLE ACCESSORIES.
1-11. The following accessories are available to in-
crease the test capabilities of the Model 427A.
1-12. CABLES AND ADAPTERS.
-hp- 110014 45" test lead, dual banana to BNC
male
-hp- 11002А 5' test lead-dual banana to alligator
clips
-hp- 110034 5" test lead-dual banana to pencil
probe and alligator clip
-hp- 10111A shielded BNC female to banana
plug adapter
1-13. PROBES.
-hp- Model 11074A 10:1 Voltage Divider Probe
extends the voltage range of Model 427А by a
factor of 10.
-hp- Model 11039A 1000:1 Capacitive Voltage
Divider for measuring voltages up to 24 KV.
-hp- Model 11096A High Frequency Probe ex-
tends the frequency range ofthe 427A to 500 MHz.
The voltage range is 0.25V to 30V.
Figure 1-2. 11096А High Frequency Probe
01791-2
1-1

e^
e
Mode1 427А
Section П
SECTION II
INSTALLATION
2-1. INTRODUCTION.
2-2. This section contains information and instruc-
tions necessary for installation and shipping of Model
427A Voltmeter. Included are initial inspection pro-
cedures, power and grounding requirements, install-
ation, and instructions for repackaging for shipment,
2-3. INITIAL INSPECTION.
2-4. This instrument was carefully inspected both
mechanically and electrically before shipment. It
should be physically free of mars or scratches and in
perfect electrical order upon receipt. To confirm
this, the instrument should be inspected for physical
damage in transit. Also, test the electrical perform-
ance of the instrument using the procedure outlined in
Paragraph 5-5. If there is damage or deficiency, see
the warranty on the inside front cover of this manual,
2-5. POWER REQUIREMENTS.
2-6. The Model 427A uses а 22. 5 volt dry cell battery
for its primary power source. However, if Option01
is included, the Model 427A can be operated from any
source of 115 or 230 volts (420%) at 50 to 400 Hz.
With the instrument disconnected from the ac power
source, move the slide switch (located on the rear
panel) until the desired line voltage appears. Power
dissipation is less than 1/2 watt maximum.
2-7. GROUNDING REQUIREMENTS.
2-8. To protect operating personnel, the National
Electrical Manufacturers' Association (NEMA) recom-
mends that the instrument panel and cabinet be ground-
ed. The Option 01 427A is equipped with a three-
conductor power cable which, when plugged into an
appropriate receptacle, grounds the instrument. The
offset pin on the power cable three-prong connector
is the ground wire.
2-9. To preserve Ше protectionfeature when operating
the instrument from atwo-contact outlet, use а three-
prong to two-prong adapter and connect the pigtail on
the adapter to ground.
2-10. INSTALLATION.
2-11. The Model 427A is fully transistorized; there-
fore, no special cooling is required. However, the
instrument should not be operated where the ambient
temperature exceeds +559С (1310F). For additional
information, address inquiries to your local -hp-
Sales and Service Office. (See Appendix B for office
locations. )
2-12. BENCH MOUNTING,
2-13, Model 427A is shipped with plastic feet and tilt
stand in place, ready for use as а bench instrument.
01791-3
2-14. RACK MOUNTING.
2-15. Model 427A may be rack mounted by using an
Adapter Frame (-hp- Part No. 5060-0797). The adapt-
er frame is a rack frame that accepts any combination
of submodular units. It can be rack mounted only.
2-16. COMBINATION MOUNTING,
2-17. The Model 427A may be mounted incombination
with other submodular units by using a Combining Case
(-һр- Model 1051A). If the 427A is equipped witha
carrying handle, it will be necessary to remove the.
top cover on 427A before inserting it into the Com-
bining Case, The Combining Case is a full-module
unit which accepts various combinations of submodular
units. Being a full-module unit itself, itcan be bench
or rack mounted and is analogous to any full-module
instrument.
2-18. REPACKAGING FOR SHIPMENT.
2-19. The following paragraphs contain а general guide
for repackaging ofthe instrumentfor shipment, Refer
to Paragraph 2-20 if the original container is to be
used; 2-21 if it is not,
NOTE
If the instrument is to be shipped to
Hewlett-Packard for service or repair,
attach a tag to the instrument identifying
the owner and indicating the service or
repair to be accomplished; include the
model number and full serial number of
the instrument. In any correspondence,
identify the instrument by model number,
serial number, and serial number prefix.
2-20. If original container is to be used, proceed as
follows:
a. Place instrument in original container. If
original container is not available, a suitable
container can be purchased from your near-
est -hp- Sales and Service Office.
b, Ensure that container is well sealed with
strong tape or metal bands.
2-21, И original container is notto ре used, proceed
as follows:
a. Wrap instrument in heavy paper or plastic
before placing in an inner container.
b. Place packing material around all sides of in-
strument and protect panel face with cardboard
strips.
c. Place instrument and inner container inaheavy
cartonor wooden box and seal with strong tape
or metal bands.
d. Mark shipping container with "DELICATE
INSTRUMENT," "FRAGILE" etc,
2-1

Қ шек TET сесия таче tn oe wama =
Section
Ш
Model
427A
a
í
MODEL 427A FRONT PANEL MODEL 427А REAR PANEL (OPTION Ol)
HEWLE1) - PACKARD //7 427А VOLTMETER
4)
FUNCTION RANGE
АСУ хок
IO XIOOK
5
ре 30 хм
( IOO хюм
N
300
>
1000 — ону
ос ZERO/I 00
427А-8-0529
BATT/LINE
(option
01
only)
slide
switch:
Se-
COM
terminal:
Connects
to
instrument
com-
lects either battery or line operation. mon. (Common input for ACV, OHMS and
DCV.)
115/230
slide
switch
(option
01
only):
Selects
either
115
Vac
or
230
Vac
for
line
operation.
VOLTS
terminal:
Applies
unknown
ac
or
dc
voltage
to
instrument.
Line input (option 01 only): Connects ac
erati er to instrument.
op
ing
pow
жігі:
2
FUNCTION
switch:
Selects
mode
of
operation.
Selections are OFF, BATT, +DC, -DC, OHMS
and AC.
RANGE switch: Selects appropriate range of
unknown input.
e ©
DC
ZERO/2
«thumbwheel:
Usedto
electrical-
Mechanical
zero:
Mechanically
zeroes
the
ly
zerothe
instrument
in
DC
mode
and
to
infinity-
meter,
set
the
instrument
in
OHMS
mode.
©
Meter face: Displays the magnitude of unknown
OHMS
terminal:
Connects
unknown
resistance
resistance
or
voltage
in
ohms
or
volts
respec-
to instrument. tively.
о 00000
е ғ
Figure
3-1.
Location
of
Front
Panel
Controls
and
Indicators
3-0
01791-2

жө
Model 427A
SECTION
INSTRUCTIONS
OPERATING
3-1. INTRODUCTION.
3-2. The Model 427А may be operated ав а дс volt-
meter, ac voltmeter, ohmmeter or dB meter. This
section contains operating instructions for each mode
of operation.
3-3. FRONT AND REAR PANEL DESCRIPTION.
3-4. Figure 3-1 shows the location of all the Model
427A controls and indicators and explainsthe function
of each. Тһе Option 01 rear panel is shown, Тһе
standard rear panel is blank.
3-5. OPERATING INSTRUCTIONS.
NOTE
To obtain maximum battery life,
set the FUNCTION switch of OFF
when the instrument is not in use.
3-6. MECHANICAL ZERO ADJUSTMENT.
3-7. Before any measurements are made, complete
the Mechanical Zero Adjustment inthe following steps.
а. Be sure instrument has been off for at least
one minute.
b. Rotate Mechanical Zero Adjustment screw
CLOCKWISE until meter pointer istothe left
of zero and moving upscale toward zero.
c. Continue to rotate adjustment screw clockwise,
STOP when needle is exactly on zero, If
needle overshoots, repeat step b.
а. When pointer is exactly over zero, rotate
adjustment screw slightly COUNTERCLOCK-
WISE to relieve tension on suspension. И
the pointer іпоуев to the left, repeat whole
procedure, but make the counterclockwise
rotation less.
3-8. TURN-ON PROCEDURE.
3-9, STANDARD INSTRUMENT,
a, Rotate the FUNCTION Switch to BATT/1. 5
MIN position,
b. Тһе meter should read 1. 5 or higher on the
0-3 scale on any range, indicating that the
battery voltage is 15 volts or higher. И the
reading is below 1.5, replace the battery
according to the steps in Paragraph 5-54.
01791-2
Section ІП
3-10. OPTION 01 INSTRUMENT.
а.
3-11.
а.
b.
с.
е,
3-12.
а.
Select either battery ог line operation withthe
rear panel BATT/LINE slide switch. H bat-
tery operation is selected, check the battery
according to Paragraph 3-9.
If line operation is selected, set the 115/230
slide switch to indicate the proper line volt-
age,
Rotate the FUNCTION switch to the desired
function. During line operation, the BATT/
1.5 MIN check position displays the output of
the Option 01 power supply. The reading
should be 1,5 or higher on the 0-3 scale оп
any range, indicating а power supply output
of 15 volts or more. This serves as а соп-
venient check of the Option 01 power supply.
DC MEASUREMENTS.
Rotate the FUNCTION switch to +DCV or
-DCV depending on the polarity of the input.
Short the VOLTS input tothe COM input, го-
tate RANGE to 0. 1, and adjustthe DC ZERO/
Өс thumbwheel for zero meter deflection.
Remove shorting connection. Н there is a
zero offset with COM and VOLTS open, refer
to Paragraph 4-16 and Paragraph 5-30.
Select approximate range of input with RANGE
switch,
DO NOT APPLY MORE THAN
1200 VDC TO ANY DC RANGE.
Connect input across VOLTS and COM ter-
minals and read magnitude of input on meter.
RESISTANCE MEASUREMENTS.
DAMAGE ТО 427A INPUT CIR-
CUIT МАҮ RESULT IF DC OR
AC VOLTAGE IS APPLIED TO
OHMS TERMINAL.
Rotate the FUNCTION switch to OHMS.
Selectthe approximate range withthe RANGE
switch; and withthe input terminals open, ай-
just the DC ZERO/Qe thumbwheel for an =
indication onthe ohms scale. (Pointer should
rest on the mark just to the left of х).
3-1