TM 11-6625-1541-15
DEPARTMENT OF THE ARMY TECHNICAL MANUAL
OPERATOR, ORGANIZATIONAL, DS, GS,
AND DEPOT MAINTENANCE MANUAL
HEWLETT-PACKARD RMS VOLTMETER
MODEL 3400A
HEADQUARTERS, DEPARTMENT OF THE ARMY
MAY 1967
WARNING
DANGEROUS VOLTAGES
EXIST IN THIS EQUIPMENT
Be careful when working the power supplies and their circuits, or on the 230- or 115-volt ac line connections.
DO NOT
TAKE CHANCES!
TM 11-6625-1541-15
Model 3400A
Section
I GENERAL INFORMATION
1-A.1 Scope
1-A.2 Index of Publications . . . 1-0.1
1-A.3 Forms and Records . . . . . .1-0.1.
1-3. Description . . . . . . . . . . . . . .1-1
1-8. Specifications. . . . . . . . . . . . . 1-1
1-10. Instrument Identification . . . . . . . 1-1
1-12. Equipment Supplied . . . . . . . . . . 1-1
1-14. Accessory Equipment Available . . . 1-1
Section Page
II INSTALLATION . . . . . . . . . . . . ...2-1
2-1. Introduction . . . . . . . . . . . . . . 2-1
2-3. Initial Inspection . . . . . . . . . . . 2-1
2-5. Power Requirements . . . . . . . . . 2-1
2-8. Installation . . . . . . . . . . . . ..2-1
2-10.
Adapter Frame Part No.
2-12.
2-14. Repackaging for Shipment. . . . . . . 2-1
Section Page
III OPERATING INSTRUCTIONS . . . . . . . . 3-1
3-1. Introduction . . . . . . . . . . . . . . 3-1
3-3. Controls and Indicators. . . . . . . . 3-1
3-5. Turn On Procedure . . . . . . . . . 3-1
3-7. Operating Instructions . . . . . . . . 3-1
3-9. Applications. . . . . . . . . . . . . . 3-1
3-11.
3-13.
3-15.
Section
IV THEORY OF OPERATION. . . . . . . . . . 4-1
4-1. Introduction . . . . . . . . . . . ...4-1
4-3. General Description. . . . . . . . . . 4-1
4-11. Detailed Description . . . . . . . . . 4-1
4-12.
4-15.
4-19.
4-22.
4-27.
4-37.
4-40.
4-48. Neon Lamp Drive Oscillator. . . . 4-3
. . . . . . . . . . . . . . . . . . . 1-0.1
Combining Case Models 1051A
or 1052A) . . . . . . . . . . . . . 2-1
5060-0797). . . . . . . . . ...2-1
RMS Value of AC Signals with DC
Component . . . . . . . . . . . . 3-1
RMS Current . . . . . . . . . . . . 3-1
RMS AC-to-DC Converter. . . . . 3-1
Input Attenuator Assembly A1. . . 4-1
Impedance Converter Assembly A2. 4-1
Second Attenuator Assembly A3. . 4-2
Video Amplifier Assembly A4. . . 4-2
Modulator/Demodulator Assembly
A5, Chopper Amplifier Assembly,
and Thermocouple Pair Assembly
(part of A4) . . . . . . . . . . . . 4-2
Power Supply Assembly A7 . . . . 4-3
Regulator Operation . . . . . . . . 4-3
TABLE OF CONTENTS
Page
1-0.1
Page
Table of Contents
List of Tables
Section Page
V MAINTENANCE . . . . . . . . . . . . ...5-1
5-1. Introduction . . . . . . . . . . . . . . 5-1
5-3. Test Equipment. . . . . . . . . . . . 5-1
5-5. Performance Checks . . . . . . . . . 5-1
5-7.
5-9.
5-11.
5-13.
5-15.
5-17. Repair Procedures . . . . . . . . . . 5-3
5-18.
5-20.
5-23.
5-25. Adjustment and Calibration Proce -
5-29.
5-31.
5-36.
5-41. Troubleshooting Procedure. . .
5-50. Neon Subassembly Replacement
Section
VI CIRCUIT DIAGRAM . . . . . . . . . .
6-1. Introduction . . . . . . . . . . .
6-3. Schematic Diagrams . . . . . .
6-6. Parts Location Diagrams. . . .
Accuracy, Linearity, and DC Output
Performance Checks. . . . . . . 5-1
Frequency Response Performance
Check . . . . . . . . . . . . ...5-2
Input Impedance Performance
Check . . . . . . . . . . . . ...5-2
Crest Factor Performance Check. 5-3
Residual Noise Performance
Check . . . . . . . . . . . . ...5-3
Cover Removal. . . . . . . . . . . 5-3
Servicing Etched Circuit Board . . 5-4
Thermocouple Replacement . . . . 5-4
dure. . . . . . . . . . . . . . . . .
Meter Zero . . .
Power Supply Checks . . . .
Low Frequency Calibration .
High Frequency Calibration .
. . .
. . .
. . . 5-6
. . . 5-6
. . . 5-6
. . . 5-7
. . . 5-15
. . . . 6-1/6-2
. . 6-1/6-2
. . . 6-1/6-2
.
. . 6-1/6-2
5-5
5-5
Page
01768-2
i
TM 11-6625-1541-15
Section
I
Figure 1-1 and Table 1-1
Model 3400A
Figure 1-1.
Table 1-1. Model 3400A Specifications
RANGE: 12 full scale ranges from 1 mv to 300 v
in a 1, 3, 10 sequence. -72 to +52 dbm.
(Usable indications to 100 µv.)
METER SCALES: Voltage, 0. 1 to 1 and 0.3 to 3.
Decibel, -12 to +2 dbm (0 dbm = 1 mw, 600
ohms). Scales are individually calibrated to
the meter movement.
FREQUENCY RANGE: 10 cps to 10 Mc.
3 to 10 Mc. (Usable readings to 5 cps and 20
Mc. )
RESPONSE: Responds to rms value (heating value)
of the input signal for all waveforms.
CREST FACTOR: (ratio of peak amplitude to rms
amplitude): 10 to 1 at full scale (except where
limited by maximum input), inversely proportional to pointer deflection, e.g. 20 to 1 at halfscale, 100 to 1 at tenth-scale.
ii
Model 3400A RMS Voltmeter
MAXIMUM INPUT: 1000 v peak.
INPUT IMPEDANCE: From 0.001 v to 0. 3 v
Range: 10 megohms shunted by 40 pf. From
1.0 v to 300 v Range: 10 megohms shunted by
15 pf.
RESPONSE TIME: Typically <2 sec. to within
1% of final value for a step change.
OVERLOAD PROTECTION: 30 db or 1000 v peak,
whichever is less, on each range.
OUTPUT: Negative 1 vdc at full scale deflection,
proportional to pointer deflection (from 10-
100% of full scale). 1 ma maximum. Nominal
source impedance is 1000 ohms.
approximately 7 watts.
DIMENSIONS: 5-1/8 in. wide, 6-1/2 in. high, 11
in. deep (1/3 module). (130 x 165 x 279 mm).
WEIGHT: Net, 7-1/4 lbs. (3,3 kg) Shipping, 11
lbs. (5 kg).
01768-2
11-6625-1541-15
This manual contains Copyrighted material originally prepared by
1-A.1. Scope
Voltmeter Model 3400A serial numbers prefixed by 528, 401, and 322. It
organizational, direct support (DS), general support (GS), and depot
maintenance.
1-A.2. Index of Publications
new editions, changes, or additional publications pertaining to the
equipment.
bulletins, supply manuals (types 7, 8, and 9), supply bulletins, lubrication
orders,
supply channels. The index lists the individual parts (-10, -20, 35P, etc.)
and the latest changes to and revisions of each equipment publication.
1-A.3. Forms and Records
This manual describes Hewlett-Packard (Federal Supply Code
includes installation and operation instructions and covers operators,
This manual does not include a basic issue items list.
Refer to the latest issue of DA Pam 310-4 to determine whether there are
DA Pam 310-4 is an index of current technical manuals, technical
and modification work orders that are available through publications
Hewlett-Packard Co.
Section I
GENERAL INFORMATION
14493)
RMS
a. Reports of Maintenance and Unsatisfactory Equipment. Use equipment
forms and records in accordance with instructions in TM 38-750.
b. Report of Damaged or Improper Shipment. Fill out and forward DD Form 6
(Report of Damaged or Improper Shipment) as prescribed in AR 700-58 (Army),
NAVSANDA Publication 378 (Navy), and AFR 71-4 (Air Force).
c. Reporting of Equipment Manual Improvements.
omissions, and recommendations for improving this manual by the individual
user is encouraged.
Changes to Publications) and forwarded direct to Commanding General, U. S.
Army Electronics Command, ATTN: AMSEL-MR-NMP-AD, Fort Monmouth, N.J. 07703.
Reports should be submitted on DA Form 2028 (Recommended
Report of errors,
1-0.1
TM 11-6625-1541-15
Model 3400A
This manual contains the information necessary for operating
and servicing the standard Model 3400A RMS Voltmeter and
the Model 3400A/Option 01 RMS Voltmeter (DB scale uppermost).
SECTION I
GENERAL INFORMATION
1-1. INTRODUCTION.
1-2. This section contains general information about
the Model 3400A RMS Voltmeter (Figure 1-1). Included are discussions of the description and purpose, instrument identification, equipment supplied,
and accessory equipment available. Also included
is a table of instrument specifications.
1-3. DESCRIPTION AND PURPOSE.
1-4. The Model 3400A RMS Voltmeter measures the
actual root-means-square (RMS) value of ac voltages
between 100 microvolt and 300 volts.
range is from 10 cps to 10 Mc.
measurements of nonsinusoidal waveforms with crest
factors (ratio of peak voltage to rms voltage) of 10
can be made.
1-5. Ac voltages are measured with a specified full-
scale accuracy of ±1% from 50 cps to 1 Mc, ±2% from
1
MC to 2 Mc,±3% from 2 Mc to 3 Mc, and ±5% from
10 cps to 50 cps and 3 Mc to 10 Mc. A single front
panel control selects one of 12 voltage or decibel
ranges.
1-6. The Model 3400A crest factor rating is 10:1
which enables full scale readings for pulses which
have a 1% duty cycle. At 1/10th of fu11 sca1e, pulse
trains with 0. 01% duty cycle (100:1 crest factor) can
be accurately measured.
1-7. The Model 3400A provides a dc output which
is proportional to the front panel meter reading. By
using this voltage to drive auxiliary equipment, the
Model 3400A functions as an rms ac-to-dc converter.
1-8. SPECIFICATION.
1-9. Table 1-1 contains the specifications for the
Model 3400A.
Frequency
Full scale
Paragraphs 1-1 to 1-15
Tables 1-2 and 1-3
SCOPE
1-10. INSTRUMENT IDENTIFICATION.
1-11. Hewlett-Packard uses a two-section eight-digit
serial number (000-00000). If the first three digits
of the serial number on your instrument do not agree
with those on the title page of this manual, change
sheets supplied with the manual will define differences
between your instrument and the Model 3400A descri-
bed in this manual.
1-12.
1-13.
is listed and described in Table 1-2.
1-14. ACCESSORY EQUIPMENT AVAILABLE.
1-15. The accessory equipment available is listed
in Table 1-3.
EQUIPMENT SUPPLIED.
The equipment supplied with each Model 3400A
Table 1-2. Equipment Supplied
IDENTIFICATION
QUANTITY 1DESCRIPTION
NUMBER
10110A
1
8120-0078
03400-90003
1
Table 1-3. Accessory Equipment Available
IDENTIFICATION
NUMBER
10503A
DESCRIPTION
Cable (Male BNC to male
BNC, 48 inches)
11OO1A
Cable (Male BNC to dual
banana plug, 45 inches)
11OO2A
Test Lead (dual banana plug
to alligator clip, 60 inches
11OO3A
Test Lead (dual banana plug
to probe and alligator clip,
60 inches)
Section I
Adapter (BNC to
dual banana jack)
Power Cord
Operating and
Service Manual
01768-2
1-1
TM 11-6625-1541-15
Model 3400A
SECTION II
INSTALLATION
2-1. INTRODUCTION.
2-2. This section contains information and instructions
necessary for installation and shipping of the
3400A RMS Voltmeter. Included are initial inspection
procedures, power requirements, installation information, and instructions for repackaging for shipment.
2-3. INITIAL INSPECTION.
2-4. The Model 3400A RMS Voltmeter received a
careful mechanical and electrical inspection before
shipment. As soon as the Model 3400A is received,
verify that the contents are intact and as ordered.
Although the instrument should be free of mars and
scratches and in perfect electrical condition, it should
be inspected for any physical damge which may have
been incurred in transit. Also test the electrical
performance of the instrument using the procedures
given in paragraph 5-5 .
shipping of the instrument become necessary, refer
to paragraph 2-14 for repackaging and shipping
instructions.
Model
Should
Paragraphs 2-1 to 2-17
2-12. ADAPTER FRAME Part No. 5060-0797).
2-13. The adapter frame is a rack frame that accepts
any combination of submodular units. It can be rack
mounted only.
Section II
2-14. REPACKAGING FOR SHIPMENT.
2-15. The following paragraphs contain a general
guide for repackaging for shipment. Refer to paragraph 2-16 if the original container is to be used:2-17
if it is not.
2-5. POWER REQUIREMENTS.
2-6. The Model 3400A can be operated from any ac
source of 115- or 230-volts (±10%), at 50 to 60 cycles.
With the instrument disconnected from the ac power
source, move the slide switch (located on the rear
panel) until the desired line voltage value appears.
The ac line fuse is a 0.25 amp, fast blow type for 115or 230-volt operation. Power dissipation is approximately 7 watts.
2-7. The Model 3400A is equipped with a three-prong
power cord. To protect operating personnel, it is
necessary to preserve the grounding feature of this
plug when using a two contact ac outlet. Use a threeprong to two-prong adapter and connect the green
pigtail lead on the adapter to ground.
2-8. INSTALLATION.
2-9. The Model 3400A is a submodular unit suitable
for bench top use. However, when used in combination
with other submodular units it can be bench and/or
rack mounted.
frame are designed for this purpose.
2-10 COMBINING CASE (
2-11. The combining case is a full-module unit which
accepts various combinations of submodular units.
Being a full-module unit, it can be bench or rack
mounted and is analogous to any full-module instrument.
01768-1
The combining case and adapter
Models 1051A or 1052A)
2-16. If original container is to be used, proceed as
follows:
Place instrument in original container if avail-
a.
able.
b. Ensure that the container is well sealed with
strong tape or metal bands.
2-17. If original container is not to be used, proceed as follows:
a. Wrap instrument in heavy paper or plastic
before placing in an inner container.
b. Use packing material around all sides of
instrument and protect panel face with cardboard
strips.
Place instrument and inner container in a
c.
heavy carton or wooden box and seal with strong
tape or metal bands.
d. Mark shipping container with “DELICATE
INSTRUMENT,“ “FRAGILE,“ etc.
2-1
TM 11-6625-1541-15
Section III
Figure 3-1
Model 3400A
Direct reading meter: dc meter which indicates
1.
rms voltage level of input signal.
2.
Mechanical zero adjustment: screwdriver
adjustment for zero of direct reading meter.
LINE ON pilot lamp: neon lamp which
3.
indicates when power is applied to instrument
and power switch is ON.
Power switch: two-position toggle switch which
4.
applies 115- or 230-volts ac to instrument.
RANGE switch: 12-position rotary switch
5.
which selects various attenuation ranges
available within Model 3400A.
INPUT connector: BNC jack which enables
6.
application of input signal to instruments
measuring circuits.
Figure 3-1.
3-0
7.
l15/230-volt switch: two-position slide switch
which sets instrument to operate from either
a 115- or 230-volt ac source.
8.
Input power jack: three-prong jack which
enables application of line voltage to instruments power supply circuits.
115V/230V/.25A FUSE: 0.25 ampere fuse
9.
which provides protection against line voltage
surges.
10.
DC OUT jack: telephone-type jack which provides negative 1-volt dc out at full scale deflection, output is proportional to meter deflection.
Model 3400A Controls and Indicators
Output impedance is 1000 ohms.
01768-1
Model 3400A
SECTION Ill
OPERATING INSTRUCTIONS
INTRODUCTION.
3-1.
This section consists of instructions and infor-
3-2.
mation necessary for the operation of the
3400A RMS Voltmeter. This section contains identi-
fication of controls and indicators, turn-on pro-
cedures, and operating instructions. Also included
is a discussion of the applications for the Model
3400A.
3-3. CONTROLS AND INDICATORS.
Each operating control, connector, and indicator
3-4.
located on the Model 3400A is identified and described
in Figure 3-1. The description of each component is
keyed to an illustration of that component which is
included within the figure.
3-5.
TURN ON PROCEDURE.
To turn on the Model 3400A, proceed as follows:
3-6.
a. Set 115/230 switch (7, Figure 3-1) to correct
position for input line voltage.
b. Apply ac voltage to Model 3400A
power cord into input power jack (8) ac receptacle.
c. Operate power switch (4) to ON ensure that
LINE indicator (3) lights.
NOTE
Allow five minutes for the Model
3400A to warm up and stabilise
before making a reading.
3-7.
OPERATING INSTRUCTIONS.
DO NOT MEASURE SIGNAL ABOVE
100 VOLTS WITH 10 TO 1 CREST
FACTOR. OTHERWISE,
THE MAXIMUM INPUT RATING (1000 VOLTS
PEAK) WILL BE EXCEEDED.
WHEN MEASURING SIGNALS UP TO
100 VOLTS RMS WITH A 10 TO 1
CREST FACTOR, USE THE BNC TO
DUAL BANANA JACK, ACCESSORY
10110A, SUPPLIED WITH THE
INSTRUMENT, OR OTHER INPUT
TEST LEADS AND CONNECTIONS
THAT WILL WITH STAND THE
MAXIMUM INPUT OF 1000 VOLTS
PEAK.
3-8. To operate the Model 3400A as an rms voltmeter proceed as follows:
a. Attach test lead to INPUT connector (6, Figure
3-l). (See Table 1-3 for a list of test leads available. )
b. Set RANGE switch (5) to 300 VOLTS position.
Model
by plugging
TM 11-6625-1541-15
Paragraphs 3-1 to 3-16
WHEN MEASURING AN AC SIGNAL
SUPERIMPOSED ON A DC LEVEL,
ALWAYS SET THE RANGE SWITCH
TO THE 300 VOLT POSITION
BEFORE MAKING THE INITIAL
CONNECTION TO A CIRCUIT SINCE
A HIGH VOLTAGE TRANSIENT DUE
TO THE APPLICATION OF A DC
VOLTAGE WILL DAMAGE THE
INPUT CIRCUITRY.
c. Connect test lead to point to be measured.
d. Rotate RANGE switch in a counterclockwise
direction (decreased attenuation) until direct reading meter (1) indicates on upper two thirds of
scale.
3-9.
APPLICATIONS.
The Model 3400A can be used in conjunction
3-10.
with other test instruments to measure the rms
value of ac signal with a dc component, measure rms
current and act as an rms ac-to-dc converter.
3-11. RMS VALUE OF AC SIGNALS WITH DC
COMPONENT.
3-12. Since the 3400A is an ac device it will meas-
ure only the rms value of the ac component of a wave.
If it is necessary to include the rms value of the dc component when measuring a signal use a Model 412A
DC Voltmeter to measure the dc component. Sub-
stitute the reading from the Model 412A and Model
3400A in the following formula:
3-13. RMS CURRENT.
3.14 To measure rms current, use an
AC Current Probe. This probe clips around the
current conductor and provides an output voltage that
is proportional to the current being measured. Using
this method, rms currents of one milliampere to one
ampere can be measured.
3-15. RMS AC-TO-DC CONVERTER.
3-16. Since the Model 3400A is provided with a dc out-
put (10, Figure 3-1) which is proportional to the meter
deflection, it can be used as a linear rms ac to dc con-
verter. The dc output can be used to drive a
3440A Digital Voltmeter for high resolution measure-
ments and/or a Mosely Model 680 St rip Chart Recorder
where an analog record is desired. External loading
does not affect the meter accuracy so that both the meter
and dc output can be used simultaneously.
Section III
Model 456A
Model
01768-2
3-1
4-0
Figure 4-1.
TM 11-6625-1541-15
Section IV
Figure 4-1
01768-1
Model 3400A
Model 3400A
TM 11-6625-1541-15
Section IV
Paragraphs 4-1 to 4-17
SECTION IV
THEORY OF OPERATION
4-1. INTRODUCTION.
4-2. This section contains the theory of operation
of the Model 3400A RMS Voltmeter. Included is a
general and detailed description of the theory of
operation.
4-3. GENERAL DESCRIPTION.
4-4. The Model 3400A comprises two attenuators, an
impedance converter, a video amplifier, a modulator/
demodulator, a chopper amplifier, an emitter follower,
a thermocouple pair, and a direct reading meter. (See
Figure 4-1.)
4-5. A signal being measured with the Model 3400A
is applied to input attenuator A1 through the INPUT
jack, located on the Model 3400A front panel.
input attenuator has an input impedance of over 10
megohms and provides two ranges of attenuation.
The output of the input attenuator is applied to impedance converter A2.
a non-inverting unity voltage gain amplifier. It presents a high impedance to the input signal and provides a low impedance output to drive the second
attenuator A3. The second attenuator provides 6
ranges in a 1, 3, 10 sequence. The two attenuators
are switched to provide 12 ranges of attenuation.
4-6. The output of the second attenuator is amplified
by video amplifier A4. The video amplifier is a wideband, five stage amplifier. The overall gain of the
video amplifier is controlled by an ac feedback loop.
The ac output of the amplifier is applied to TC401;
one of the thermocouples of the thermocouple pair.
The impedance converter is
The
4-9. The thermocouple pair acts as a summing point
for the ac output of the video amplifier A4 and the dc
output of the emitter follower. The difference in the
heating effect of these voltages is felt as a dc input to
modulator A5. This difference input is amplified and
is fed to TC402 and to meter Ml.
voltage rep resents the rms value of the ac signal
applied at the INPUT jack.
4-10. The dc voltage driving meter M1 is also
available at the DC OUT jack, located at the rear of
the Model 3400A.
4-11. DETAILED DESCRIPTION.
4-12. INPUT ATTENUATOR ASSEMBLY Al.
4-13. The input attenuator assembly is a capacitive-
compensated attenuator which provides two ranges of
attenuation for the 12 positions of the RANGE switch.
See input attenuator schematic diagram illustrated on
Figure 6-1.
4-14. When the RANGE switch is positioned to one
of the six most sensitive ranges (.001 to .3 VOLTS),
the attenuator output voltage is equal to the input
voltage. When the RANGE switch is positioned to
one of six highest ranges (1 to 300 VOLTS), the
input signal is attenuated 60 db (1000:1 voltage divi-
sion) by the resistive voltage divider consisting of
R101, R103, and R104. Trimmer C102 is adjusted at
100 kc, and R104 is adjusted at 400 cps to provide
constant attenuation over the input frequency range.
4-15. IMPEDANCE CONVERTER ASSEMBLY A2.
This amplified dc
4-7. The dc output of TC401 is modulated by mod-
ulator A5. The modulator comprises two photocells
which are alternately illuminated by two neon lamps
which in turn are controlled by the oscillator located
on power supply assembly, A7. Also applied to one of
the photocells is the TC401 dc output. The resultant
output of the modulator is a square wave whose ampli-
tude is proportional to the dc input level.
4-8. The square wave output of the modulator is
amplified by chopper amplifier A6. The chopper
amplifier is a three-stage, high gain ac amplifier.
Its output is applied to demodulator A5. The demod-
ulator output is a dc level whose magnitude is pro-
portional to the amplitude of the ac input. The de-
modulator output is applied to a two-stage, direct
coupled emitter follower. The emitter follower is
used to make the impedance transformation from
the high impedance output of the demodulator to the low
impedance of the direct reading meter Ml and TC402;
the second thermocouple of the thermocouple pair.
01768-2
4-16. The impedance converter assembly utilizes a
nuvistor tube cathode follower circuit to match the
high output impedance of the input attenuator to the
low input impedance of the second attenuator. The
cathode follower circuit preserves the phase relationship of the input and output signals while maintaining
a gain of unity. See impedance converter assembly
schematic diagram illustrated on Figure 6-1.
4-17. The ac signal input to the impedance converter
is RC coupled to the grid of cathode follower V201
through C201 and R203. The output signal is devel-
oped by Q201 which acts as a variable resistance in
the cathode circuit of V201. The bootstrap feedback
from the cathode of V201 to R203 increases the
effective resistance of R203 to the input signal. This
prevents R203 from loading the input signal and preserves the high input impedence of the Model 3400A.
The gain compensating feedback from the plate of
V201 to the base of Q201 compensates for a decrease
in gain of V201 caused by tube aging.
4-1
TM 11-6625-1541-15
Section IV
Paragraphs 4-18 to 4-32
Model 3400A
4-18. Breakdown diode CR201 controls the grid bias
voltage on V201 thereby establishing the operating
point of this stage. CR202 across the base-emitter
junction of Q201 protects Q201 in the event of a
failure in the +75 volt power supply. Regulated dc is
supplied to V201 filaments to avoid inducing ac hum
in the signal path.
4-19. SECOND ATTENUATOR ASSEMBLY A3.
4-20. The second attenuator is a resistive divider
which attenuates the ac input signal while maintaining
a low impedance output for the following amplification
stages. See second attenuator assembly schematic
diagram illustrated in Figure 6-1.
4-21. The ac input signal is applied to a precision
resistance voltage divider consisting of R302 through
R312. These resistors are arranged to give six
attenuation ranges from 0.001 to 0.3 volts. Trimmer
capacitor C303 (. 3V ADJ) provides an adjustment for
frequency response at the higher frequencies.
4-22. VIDEO AMPLIFIER ASSEMBLY A4.
4-23. The video amplifier functions to provide constant gain to the ac signal being measured over the
Model 3400A operating ranges. See video amplifier
assembly schematic diagram illustrated on Figure
6-2.
4-24. The ac input signal from the second attenuator
is coupled through C402 to the base of input amplifier
Q401. Q401, a class A amplifier, amplifies and
inverts the signal which is then direct coupled to the
base of bootstrap amplifier Q402. The output, taken
from Q402 emitter is applied to the base of Q403 and
fed back to the top of R406 as a bootstrap feedback.
This positive ac feedback increases the effective ac
resistance of R406 allowing a greater portion of the
signal to be felt at the base of Q402. In this manner,
the effective ac gain of Q401 is increased for the mid-
band frequencies without disturbing the static operating
voltages of Q401.
4-25. Driver amplifier Q403 further amplifies the
ac signal and the output at Q403 collector is fed to
the base circuit of emitter follower Q404. The feed-
back path from the collector of Q403 to the base of
Q402 through C 405 (10 MC ADJ) prevents spurious
oscillations at high input frequencies. A dc feedback
loop exists from R433, in the emitter circuit of Q403,
to the base of Q401. This feedback stabilizes the
Q401 bias voltage. Emitter follower Q404 acts as a
driver for the output amplifier consisting of Q405 and
Q406; a complimentary pair operating as a push-pull
amplifier. The video amplifier output is taken from
the collectors of the output amplifiers and applied to
thermocouples TC401. A gain stabilizing feedback is
developed in the emitter circuits of the output ampli-
fiers. This negative feedback is applied to the emitter
of input amplifier Q401 and establishes the overall
gain of the video amplifier.
4-26. Trimmer capacitor C405 is adjusted at 10 mc
for frequency response of the video amplifier. Diodes
CR402 and CR406 are protection diodes which prevent
voltage surges from damaging transistors in the
video amplifier. CR401, CR407, and CR408 are
temperature compensating diodes to maintain the
zero signal balance condition in the output amplifier
over the operating temperature range. CR403, a
breakdown diode, establishes the operating potentials
for the output amplifier.
4-27. MODULATOR/DEMODUMTOR ASSEMBLY
A5, CHOPPER AMPLIFIER ASSEMBLY,
AND THERMOCOUPLE PAIR ASSEMBLY
(PART OF A4).
4-28. The modulator/demodulator, chopper amplifier, and thermocouple pair form a servo loop which
functions to position the direct reading meter M1 to
the rms value of the ac input signal. See modulator/
demodulator, chopper amplifier, and thermocouple
pair schematic diagram illustrated in Figure 6-3.
4-29. The video amplifier output signal is applied to
the heater of thermocouple TC401. This ac voltage
causes a dc voltage to be generated in the resistive
portion of TC401 which is proportional to the heating
effect (rms value) of the ac input. The de voltage is
applied to photocell V501.
4-30. Photocells V501 and V502 in conjunction with
neon lamps DS501 and DS502 form a modulator circuit.
The neon lamps are lighted alternately between 90
and 100 cps.
photocells. DS501 illuminates V501; DS502 illuminates V502. When a photocell is illuminated it has
a low resistance (approximately 6K ohms) compared
to its resistance when dark (approximately 500K ohms).
Therefore, when V501 is illuminated, the output of
thermocouple TC401 is applied to the input of the
chopper amplifier through V501. When V502 is
illuminated, the ground signal felt through R634 is
applied to the chopper amplifier.
illumination of V501 and V502 modulates the de input
at a frequency between 90 and 100 cps. The modulator
output is a square wave whose amplitude is proportional
to the input dc level
4-31. The chopper amplifier, consisting of Q601 through
Q603 is a high gain amplifier which amplifies the
square wave developed by the modulator. Noise and
power supply voltage variations are reduced by
breakdown diode CR601 and CR603. Diodes CR602
and CR603 are biasing diodes for Q602 and Q603
respectively. The amplified output is taken from the
collector of Q603 and applied to the demodulator
through C605.
4-32. The demodulator comprises two photocells,
V503 and V504, which operate in conjunction with
DS501 and DS502; the same neon lamps used to illumi-
nate the photocells in the modulator. Photocells V503
and V504 are illuminated by DS501 and DS502, respectively.
Each lamp illuminates one of the
The alternate
4-2
01768-2
Model 3400A
4-33. The demodulation process is the reverse of the
modulation process discussed in paragraph 4-30.
The output of the demodulator is a dc level which is
proportional to the demodulator input. The magnitude
and phase of the input square wave determines the
magnitude and polarity of the dc output level. This dc
output level is applied to the emitter follower consisting of Q604 and Q605
4-34. The emitter follower is needed to match the
high output impedance of the demodulator to the low
impedance input of the meter and thermocouple circuits. The voltage drop across CR604 in the collector
circuit of Q604 is the operating bias for Q604. This
fixed bias prevents Q604 failure when the base voltage
is zero with respect to ground.
4-35. The dc level output, taken from the emitter of
Q605, is applied to meter M1 and to the heating
element of thermocouple TC402. The voltage developed
in the resistive portion of TC402 is effectively subtracted
from the voltage in TC401. The input signal to the
modulator then becomes the difference in the dc outputs of the two thermocouples.
4-36. A frequency stabilizing feedback path exists
through C610 and C611 during one half cycle of the
modulated square wave and through C607 and C608
during the other half cycle. AC components in the
modulated square wave which are not synchronized
with the modulated square wave receive heavy attenuation due to this negative feedback. In this manner,
the chopper amplifier is effectively tuned to the mod-
ulator frequency.
4-37. POWER SUPPLY ASSEMBLY A7.
4-38. The power supply assembly provides the oper-
ating voltages for the tube and transistors used in the
Model 3400A. See power supply assembly schematic
diagram illustrated on Figure 6-4.
4-39. Either 115 or 230 volts ac is connected to the
primary of power transformer T1 through fuse F1 and
the POWER switch S1. Switch S2 (slide switch on
rear panel) connects T1 primary windings in series
for 230-volt operation or in parallel for 115-volt
operation. Neon lamp DSI lights to indicate power
ON when ac power is applied and S1 is closed.
4-40. REGULATOR OPERATION.
4-41. The series regulator acts as a dynamic variable resistor in series with the power supply output.
A control amplifier senses changes in the output
voltage by comparing the output with a fixed reference
voltage. The control amplifier then supplies any output voltage changes to the driver transistor, which in
TM 11-6625-1541-15
Paragraphs 4-33 to 4-49
turn changes the resistance of the series regulator
to oppose the change in output voltage. Diodes
across the base emitter junction of the series reg-
ulator provide over current protection.
4-42. +75-VOLT SUPPLY.
4-43. The +75-volt supply consists of a full-wave
rectifier (CR701 and CR702) whose output is filtered
by CIA and CIB and regulated by series regulator
QI. The +75-volt supply provides regulated +75 volts
which is used as the plate supply voltage for V201.
Voltage variation from the output is felt at Q702
base circuit through C704, R715, and R? 16. The
C703 and R709 network provides phase correction
for power supply stability. The regulation circuitry
is in the negative leg of the +75-volt supply. and uses
the -17.5-volt supply as a reference.
4-44. -17.5-VOLT SUPPLY.
4-45. The regulated -17.5-volt supply consists of a
full-wave rectifer (CR711, and CR712) whose output
is filtered by C706 and C708 and regulated by Q2.
Breakdown diode CR715 provides reference voltage at
the base of Q704. Regulation operation is the same
described in paragraph 4-40.
4-46. -6-VOLT SUPPLY.
4-47. The regulated-6.3-volt supply consists of a
full-wave rectifier (CR716 and CR717) whose output
is filtered by C2 and regulated by Q3. Emitter
follower Q705 is connected to the -17.5-volt supply
which provides a reference for the -6.3 volt supply.
Series regulator Q3 acts as a dynamic variable resi-
stor in series with the output to oppose changes in
output voltage.
4-48. NEON LAMP DRIVE OSCILLATOR.
4-49. The neon lamp drive oscillator consists of
transistor Q706, diode CR718, resistors R701, R702,
R712, R713, and capacitor C711. Transistor Q706
is held on (conducting) by the base bias developed at
the junction of R712 and CR718. The collector
current of Q706 charges up capacitor C711 through
R701 or R702 depending upon the illuminated neon
lamp on the Chopper Amplifier Assembly, A6. When
the capacitor reaches a sufficient charge to fire the
dark neon lamp, the illumination of the neon lamps
alternate and the capacitor discharges through the
previously dark neon lamp. With the previously dark
neon lamp illuminated, the capacitor charges up in
the opposite direction until firing the previously
illuminated neon lamp. The cycle described above
repeats at a frequency of 90 to 100 cps as determined
by the RC time constant of R701, C711, and R702,
and C711.
Section IV
01768-2 4-3
TM 11-6625-1541-15
Section V
Table 5-1
Model 3400A
INSTRUMENT
TYPE
DC Voltmeter/
Ohmmeter
Voltmeter Cali-
brator
Oscillator Model 651A Test Os-
Frequency Re-
sponse
Oscilloscope
Pulse Generator
Pulse Counter
REQUIRED CHARACTERISTICS
Voltmeter
Accuracy: ±. 1% full scale
Voltage Range: 10 mv to 100 v
Ohmmeter
Accuracy: ±3%
Ohms Range:
Voltage Range: 1 mv to 300 v rms
Frequency: 400 cps
Accuracy: ±0.2%
Frequency Stability: .001%/minute
Frequency Range: 10 cps to 10 Mc
Frequency Range (with external os-
cillator): 15 cps to 10 Mc
Frequency Response: ±0.5%, 15 cps to ment
10 Mc
Sensitivity: 0.1 v/cm
Bandwidth: 2 cps to 50 Mc
Pulse Width: variable to 10
Pulse Amp: ±2 volts peak, variable
Pulse Rate: 250 to 1000 pps
Range: 250 to 1000 pps
Accuracy: ±1 count
Table 5-1. Required Test Equipment
USE
Performance Checks
Power Supply Checks
Alignment and Adjust-
ment
Troubleshooting
Performance Checks
Alignment and Adjust-
ment
Performance Checks
Alignment and Adjust-
ment
Troubleshooting
Performance Checks
Alignment and Adjust-
Performance Checks
Power Supply Checks
Troubleshooting
Performance Checks
Performance Checks
RECOMMENDED MODEL
Model 3440A/3444A
Digital Voltmeter
Model 738B Voltmeter
Calibrator
cillator
Model 739AR Frequen
cy Response Test Set
Model 175A/1752B
50 Mc Oscilloscope
Model 212A Pulse
Generator
Model 5512A Elec-
tronic Counter
AC Voltmeter
Power Supply
tor
50 Feed-Thru
Termination
BNC-T-Adapter
Adapter-Con-
nector
5-0
Voltage Range: 1 to 150 v Power Supply Checks
Accuracy: ±3%
Output: 0 - 1 vdc, variable
Metal film, 1/4 w, 1%
Resistor: fixed, composition, 50
ohms ±5%, 1/4 w
UG-274B/U
UG-201A/U
Troubleshooting
Troubleshooting
Performance Checks
Performance Checks
Alignment and Adjust-
ment
Performance Checks
Alignment and Adjust-
ment
Performance Checks
Alignment and Adjust-
ment
Model 403A/B AC
Voltmeter
Model 721A
Part No. 0757-0782
Model 11048B 50 Ohm
Feed-Thru Termination
Part No. 1250-0072
Part No. 1250-0067
01768-2
Model 3400A
SECTION V
MAINTENANCE
5-1. INTRODUCTION.
5-2. This section contains the information necessary
for maintenance of the Model 3400A RMS Voltmeter.
Included are performance checks, repair procedures,
adjustment and calibration procedures, and troubleshooting techniques.
5-3. TEST EQUIPMENT.
The test equipment required for the maintenance
5-4.
of the Model 3400A is listed in Table 5-1. Equipment
having similar characteristics may be substituted for
the equipment listed.
5-5. PERFORMANCE CHECKS.
5-6. The performance checks presented in this sec-
tion are front-panel procedures designed to compare
the Model 3400A with its published specifications.
These checks can be incorporated in periodic maintenance, post-repair, and incoming quality control in-
spection. These checks should be conducted before
any attempt is made at instrument calibration.
all performance checks, periodically vary the Model
3400A line voltage ± 10%.
NOTE
Allows 30-minute warm-up period
before making performance checks.
5-7. ACCURACY, LINEARITY, AND DC OUTPUT
PERFORMANCE CHECK.
5-8. The accuracy, linearity, and dc output test setup is illustrated in Figure 5-1. A Voltmeter Calibrator (Model 738B) and a DC Voltmeter
3440A 3444A) are required for this test.
During
Model
TM 11-6625-1541-15
Paragraphs 5-1 to 5-8 and Table 5-2 and Figure 5-1
a.
Connect test setup illustrated in Figure 5-1.
b.
Set Model 3400A RANGE switch to .001 posi-
tion.
c.
Adjust Voltmeter Calibrator for 0. 001 volt,
400 cps output: set dc voltmeter to measure
1 volt.
d.
If Model 3400A does not indicate within values
listed under METER READING in Table 5-2.
perform low frequency calibration procedure,
Paragraph 5-31.
e.
Dc output as indicated on dc voltmeter should
be within values listed under DC OUTPUT in
Table 5-2.
f.
Repeat steps c thru e for remaining voltage
values listed under VOLTMETER CALIBRATOR OUTPUT in Table 5-2.
Table 5-2. Accuracy, Linearity, and DC Output
Performance Check, Supplemental Data
VOLTMETER
CALIBRATOR
OUTPUT
0.001 v 0.00099 to 0.00101 0.990 to 1.01
0.003 v 0.00297 to 0.00303 0.940 to 0.960
0.1 v 0.099 to 0.101 0.990 to 1.01
0.3 v
1.0 v 0.99 to 1.01
3.0 v
30.0 v
100.0 v
300.0 v
METER
READING OUTPUT
0.297 to 0.303 0.940 to 0.960
2.97 to 3.03
29.7
99.0
297.0 to 303.0
to 30.3
to 101.0
Section V
DC
0.990 to 1.01
0.940 to 0.960
0.940 to 0.960
0.990 to 1. 01
0.940 to 0.960
01768-1
Figure 5-1. Accuracy, Linearity, and DC Output Test Setup
5-1
TM 11-6625-1541-15
Section V
Pargraphs 5-9 to 5-12 and Table 5-3 and Figure 5-2
Model 3400A
5-9. FREQUENCY RESPONSE PERFORMANCE
CHECK.
5-10. The frequency response test setup is illustrated
in Figure 5-2. A Frequency Response Test Set
Model 739AR) and an Oscillator
required for this test.
Model 651A) are
NOTE
The Frequency Response Test
Set used to check the 3400A accuracy should be calibrated at the
end of its output cable. At 10
Mc there is typically a 2% loss in
the 739A output cable.
a.
Connect test setup illustrated in Figure 5-2.
b.
Set Model 3400A RANGE switch and frequency
response test set output attenuator to 1 volt
position.
c.
Set frequency response test set to use external input.
d.
Adjust oscillator output frequency for 400 cps;
adjust oscillator output amplitude for full-scale
deflection on the Model 3400A
e.
Adjust frequency response test set meter to
convenient reference.
f.
Adjust oscillator output frequency to values
listed under FREQUENCY in Table 5-3; adjust oscillator output voltage to maintain reference set in step e. If Model 3400A does
not indicate within values under METER
READING in Table 5-3, perform high frequency calibration procedures, Paragraph 5-36.
5-11. INPUT IMPEDANCE PERFORMANCE CHECK.
5-12. An Oscillator
sistor Part No. 0757-0782) are required for the
input impedance performance check.
Model 651A) and a 200K
Set Model 3400A RANGE switch to 1 volt posi-
a.
tion.
Adjust oscillator output frequency to 50 cps;
b.
output voltage for full-scale deflection as indicated on Model 3400A.
Insert 200 K resistor in series with Model
c.
3400A input; meter reading should change lees
than 0.02 volts. This corresponds to an input impedance of 10 megohms where:
Adjust oscillator frequency to 50 Kc; Model
d.
3400A reading should be greater than 0.7
volts. This correspond to input shunt capacity of less than 15 pf.
Set Model 3400A RANGE switch to .001 posi-
e.
tion.
Repeat steps b and c.
f.
Adjust oscillator frequency to 16 Kc; Model
g.
3400A reading should be greater than 0.7
volts. This corresponds to an input shunt
capacity of less than 40 pf.
Table 5-3. Frequencv Response Performance Check.
Supplemental Data
5-2
Figure 5-2.
Figure 5-2.
01768-2
Model 3400A
TM 11-6625-1541-15
Paragraphs 5-13 to 5-19 and Figure 5-3
Section V
5-13. CREST FACTOR PERFORMANCE CHECK
5-14. The crest factor performance check test setup
is illustrated in Figure 5-3. A Pulse Generator
Model 212A), a High Frequency Oscilloscope Model
175A/1750B), and an Electronic Counter Model
5512A) are required for this test.
a. Connect test setup illustrated in Figure 5-3.
b. Set Model 3400A RANGE switch to 0. 1 volt
position.
c. Adjust pulse generator for pulse output with
following characteristics:
E peak. . . . . . . 1.00 v as indicated on os-
cilloscope
Pulse Rate . . . .
990 pps as indicated on
electronic counter
Pulse Width
. . . .
d. Model 3400A should indicate 0.1 volt (±5%).
e. Adjust pulse generator pulse rate to 250 pps
as indicated on electronic counter; this corresponds to a crest factor of 20.
f. Model 3400A should indicate 0.05 volts (±5%).
5-15. RESIDUAL NOISE PERFORMANCE CHECK.
5-16. A 100 K shielded load is required for the re-
sidual noise performance check.
a. Connect 100 K shielded load to the Model
3400A INPUT.
b. Rotate RANGE switch to 0.001. Zero offset
should be less than 5% of full scale.
5-17. REPAIR PROCEDURES.
5-18. COVER REMOVAL,
5-19. When it is necessary to repair or adjust the
Model 3400A, one or more covers will have to be removed. Refer to Figure 5-4 and the following steps
for cover removal procedure.
a. TOP COVER. Remove top cover screw; slide
cover to rear and lift to remove.
b. SIDE COVERS. Remove four screws in side
cover; lift to remove.
c. BOTTOM COVER. Remove bottom cover
screw at rear of cover. Slide cover to rear
and remove.
01768-1
Figure 5-3
5-3
TM 11-6625-1541-15
Section V
Paragraphs 5-20 to 5-24 and Figure 5-4
Model 3400A
5-20. SERVICING ETCHED CIRCUIT BOARDS.
5-21. The Model 3400A has five etched circuit
boards. Use caution when removing them to avoid
damaging mounted components. The assembly and
Part No. are silk screened on the interior of the circuit board to identify it. Refer to Section VII for parts
replacement and Part Number information.
5-22. The etched circuit boards are a plated-through
The electrical connection between sides of the
type.
board is made by a layer of metal plated through the
component holes. When working on these boards, observe the following general rules.
a. Use a low-heat (25 to 50 watts) small-tip sol-
dering iron and a small diameter rosin core
solder.
b. Circuit components can be removed by plac-
ing the soldering iron on the component lead
on either side of the board and pulling up on
lead. If a component is obviously damaged,
clip leads as close to component as possible
and then remove. Excess heat can cause the
circuit and board to separate or cause damage
to the component.
c. Component lead hole should be cleaned before
inserting new lead.
5-4
Figure 5-4.
d. To replace components, shape new leads and
insert them in holes. Reheat with iron and
add solder as required to insure a good elec trical connection.
e. Clean excess flux from the connection and ad-
joining area.
f. To avoid surface contamination of the printed
circuit, clean with weak solution of warm
water and mild detergent after repair. Rinse
thoroughly with clean water. When completely
dry, spray lightly with Krylon (#1302 or
equivalent).
5-23. THERMOCOUPLE REPLACEMENT.
CAUTION
Exercise extreme care when removing or replacing the amplifier
printed circuit board assembly
and when shaping the thermocouple
leads.
5-24. Should a thermocouple be defective, it is necessary to replace both as a matched pair (see Section
VII, Table of Replaceable Parts) to ensure for proper
operation.
To replace thermocouples, proceed as
follows:
01768-1
Model 3400A
a. Turn instrument power off and remove left
side and top covers.
b. Remove two screws in left side of amplifier
board and one screw through ground lug connecting board to chassis.
c. Lift board slightly to clear lanced guide on
chasms. Gently pull bottom of board to outside until board will drop down and top will
clear main frame. Adjust amplifier input
and output cables to ensure free passage
through grommets and carefully fold board
down to expose the four nuts holding the thermocouple shield.
d. Remove four shield nuts; lift shield off. Re-
move thermocouples, noting orientation.
e. Leads must be shaped before inserting new
thermocouples. Ensure that red dot on thermocouples face board. During the shaping
process, hold leads between bending point and
glass with long-nose pliers.
f. Carefully install new thermocouples and sol-
der, Refer to Paragraph 5-22.
g. Clean the board as discussed in Paragraph 5-22.
Carefully mask thermocouple shield during
spraying.
h. Apply silicon grease (Dow Corning 5 Compound
or equivalent) to shield contact edges.
Reverse steps d, c, b, and a for reassembly.
j.
k. Refer to Paragraph 5-25 and calibrate the am-
plifier.
TM 11-6625-1541-15
Paragraphs 5-25 to 5-28 and Table 5-4
5-25. ADJUSTMENT AND CALIBRATION
5-26. The following is a complete adjustment and calibration procedure for the Model 3400A. These operations should be conducted only if it has previously been
established by Performance Checks, Paragraphs 5-5
to 5-16, that the Model 3400A is out of adjustment. Indiscriminate adjustment of the internal controls to re-
fine settings may actually cause more difficulty. If
the procedures outlined do not rectify any maladjustments that may exist, and you have carefully rechecked
your connections and settings, refer to Paragraph 5-41,
Troubleshooting, for possible cause and recommended
corrective action.
5-27. MECHANICAL METER ZERO.
5-28. The mechanical meter zero screw is located on
the instrument front panel. If the meter pointer does
not indicate zero when the instrument power has been
off for at least one minute, mechanically zero the
meter following the procedure outlined below.
PROCEDURES.
a.
Turn instrument power off; disconnect input
signal; remove cable from J2 (DC OUT) at
rear of instrument; and allow one minute for
meter pointer to stabilize.
b.
Rotate zero adjust CW until pointer is to left
of zero, moving up scale. Continue until
pointer is at zero. If pointer overshoots zero,
repeat operation.
c.
When the pointer is exactly at zero, rotate
the adjusting screw slightly counterclockwise
to free it. If the meter pointer moves to the
left during this adjustment, repeat steps b
through c.
Section V
01768-1
Table 5-4. Power Supply Checks
5-5
TM 11-6625-1541-15
Section V
Paragraphs 5-29 to 5-39
Model 3400A
5-29. POWER SUPPLY CHECKS.
5-30. Power supply voltage and ac ripple specifications
are listed in Table 5-4. Test points are also indicated
in this table. When making ripple voltage measurements, it may be desirable to isolate the ac testing
instrument from power line ground to avoid any un-
desirable ground loop currents. Use a three-prong to
two-prong adapter in the power line receptacle.
5-31. LOW FREQUENCY CALIBRATION.
5-32. The low frequency calibration comprises the
amplifier gain adjustment, the 1/10 scale adjustment,
and the 1 volt adjustment. A Voltmeter Calibrator
Model 738B) and a DC Voltmeter Model 3440A/
3444A) are required.
5-33. AMPLIFIER GAIN ADJUSTMENT.
Connect test setup illustrated in Figure 5-1.
a.
Set Model 3400A RANGE switch to .01 volt
b.
position.
Adjust voltmeter calibrator for 0.01 volt, 400
c.
cps output; set dc voltmeter to measure 1 volt.
Remove Model 3400A top cover; adjust R4
d.
(CAL) for 1.0 volt as indicated on dc voltmeter.
If R4 (CAL) does not have enough range to
calibrate the dc output, the value of R3 should
be changed. Typical range of R3 is from 1.0
K to 2.6 K ohms.
e.
Adjust R6 (FULL SCALE ADJUST) for Model
3400A full-scale meter reading.
5-34. 1/10 SCALE ADJUSTMENT.
Connect test setup illustrated in Figure 5-1;
a.
omit dc voltmeter.
b.
Set Model 3400A RANGE switch to .1 volt
position.
Adjust voltmeter calibrator for 0.01 volt,
c.
400 cps output.
NOTE
The 1/10 SCALE ADJUST should
be set slightly low (needle’s width)
to reduce meter (needle) offset with
shorted input.
Remove Model 3400A top cover; adjust R7
d,
(1/10 SCALE ADJUST) for Model 3400A 1/10
scale meter reading.
5-35.1
VOLT ADJUSTMENT.
a.
Connect test setup illustrated in Figure 5-1.
b.
Set Model 3400A RANGE switch to 1 volt
position.
c.
Adjust voltmeter calibrator for 1.0 volt, 400
cps output.
d.
Adjust R104 (1 V ADJUST) for Model 3400A
for full-scale reading.
5-36. HIGH FREQUENCY CALIBRATION.
5-37. The high frequency calibration comprises the
amplifier gain adjustment, the input attenuator ad-
justment, and the second attenuator adjustment. A
Frequency Response Test Set Model 739AR) and
an Oscillator Model 651A) are required.
5-38. AMPLIFIER GAIN ADJUSTMENT.
NOTE
The frequency response test set
used to calibrate the 3400A should
be calibrated at the end of its
output cable. At 10 Mc there is
typically a 2% loss in the output
cable.
Connect test setup illustrated in Figure 5-2.
a.
b.
Set Model 3400A RANGE switch and frequency
response test set output attenuator to 1 mv
posit ion.
c.
Set frequency response test set to use external input.
d.
Adjust oscillator output frequency for 400 cps;
output voltage for 90% full scale as indicated
on Model 3400A meter.
e.
Adjust frequency response test set meter to
convenient reference.
f.
Adjust oscillator output frequency for 10 Mc;
output voltage to maintain reference set in
step e.
Remove Model 3400A left-side cover; adjust
g.
C405 (10 MC ADJUST) for 90% full scale as
indicated on Model 3400A meter. Replace
cover; readjust C405 if meter reading varies
from 90% full scale.
h.
Vary oscillator between 3 and 10 Mc; maintain oscillator output voltage to reference set
in step e. If Model 3400A meter reading
varies below 85’% or above 95% of full
scale, repeat step g until optimum response
is obtained between 3 and 10 Mc.
5-39. INPUT ATTENUATOR ADJUSTMENT.
NOTE
The frequency response test set
used to calibrate the 3400A should
be calibrated at the end of its
output cable,
typically a 2% loss in the output
cable.
Connect test setup illustrated in Figure 5-2.
a.
b.
Set Model 3400A RANGE switch and frequency
response test set output attenuator to 1 volt
position.
c.
Set frequency response test set to use exter-
nal input.
d.
Adjust oscillator output frequency for 400 cps;
output voltage for 90% full scale as indicated
on Model 3400A meter,
e.
Adjust frequency response test set meter to
convenient refereuce.
f.
Adjust oscillator output frequency for 100 Kc;
output voltage to maintain reference in step e.
At 10 Mc there is
5-6
01768-1
Model 3400A
TM 11-6625-1541-15
Section V
Paragraphs 5-40 to 5-49 and Table 5-5
g. Remove Model 3400A bottom cover; adjust
C102 (1 V, 100 KC ADJUST) for 90% full
scale as indicated on Model 3400A meter.
Replace cover; readjust C405 if meter reading varies from 90% full scale.
h. Vary oscillator between 100 Kc and 10 Mc;
maintain oscillator output voltage to reference
set in step e. If Model 3400A meter reading
varies more than ±1% to 1 Mc, ±2% from 1 Mc
to 2 Mc, ±3% from 2 Mc to 3 Mc, or ±5% from
3 Mc to 10 Mc, repeat step g until optimum
response is obtained.
5-40. SECOND ATTENUATOR ADJUSTMENT.
NOTE
The frequency response test set
used to calibrate the 3400A should
be calibrated at the end of its
output cable. At 10 Mc there is
typically a 2% loss in the output
cable.
Connect test setup illustrated in Figure 5-2.
a.
Set Model 3400A RANGE switch and frequency
b.
response test set output attenuator to .3 volt
position.
Set frequency response test set to use exter-
c.
nal input.
Adjust oscillator output frequency for 400 cps;
d.
output voltage for 90% full scale as indicated
on Model 3400A meter.
Adjust frequency response test set meter to
e.
convenient reference.
Adjust oscillator output frequency for 3 Mc;
f.
output voltage to maintain reference in step e.
Remove Model 3400A bottom cover; adjust
g..
C303 (.3 V ADJ) for 90% full scale as indicated
on Model 3400A meter.
Vary oscillator between 3 Mc and 10 Mc; main-
h.
tain oscillator output voltage to reference set
Table 5-5.
SYMPTOM
1/2 scale readings on all RANGE switch settings
and input voltages.
3 to 5% meter offset on all ranges with shorted in-
put.
400 cps calibration low and frequency response
falls off above 50 Kc.
I
Switching transients exceed 5% of full scale with
shorted input.
Instrument has been overloaded.
Meter jitter or flutter exceeds 0.5% of full scale.
Full-scale difference from range to range.
in step e. If Model 3400A meter reading
varies below 85’% or above 95% of full scale,
repeat step g until optimum response is ob-
tained between 3 and 10 Mc.
5-41. TROUBLESHOOTING PROCEDURE.
5-42. This section contains procedures designed to
assist in the isolation of malfunctions. These operations should be undertaken only after it has been established that the difficulty cannot be eliminated by
the Adjustment and Calibration Procedures, Paragraph 5-25. An investigation should also be made to
ensure that the trouble is not a result of conditions
external to the Model 3400A.
5-43. Conduct a visual check of the Model 3400A for
possible burned or loose components, loose connections, or any other condition which might suggest a
source of trouble.
5-44. Table 5-5 contains a summary of the front-panel
symptoms that can be used in initial efforts to select
a starting point for troubleshooting operations.
5-45. Table 5-6, in conjunction with Figure 5-5, con-
tains procedures which may be used as a guide in iso-
lating malfunctions. The steps in Table 5-6 describe
the normal conditions which should be encountered
during the checks (circled numbers in Figure 5-5.
5-46. The checks outlined in Table 5-6 are not de-
signed to measure all circuit parameters, rather,
only to localize the malfunction. Therefore, it is
quite possible that additional measurements will be
required to completely isolate the problem. Amplifier
gain may also vary slightly between instruments;
therefore, it should not be necessary to precisely
duplicate waveforms or values described.
5-47. Voltage values indicated are based on 0.1 v rms
input at 400 cps unless otherwise specified.
5-48. When required, check power supply voltages as
outlined in Paragraph 5-29.
5-49. Figures 5-6 through 5-17 are typical waveforms
in Model 3400A.
Front Panel Symptoms
POSSIBLE CAUSE
Chopper Amplifier (A6), C612.
R7 misadjusted.
C405 misadjusted.
Check Q605.
Q401 or Q402 shorted.
Check collector voltage of Q201 (should not exceed
9.0v).
Check Q201, Q401, and Q402.
Check Q601, Chopper Assembly (neons).
Check resistors in second attenuator.
01768-1
5-7
TM 11-6625-1541-15
Section V
Figure 5-5
Model 3400A
5-8
Figure 5-5. Troubleshooting Tree
01768-1
Model 3400A
Table 5-6. Troubleshooting Procedure
TM 11-6625-1541-15
Table 5-6 and Figures 5-6 thru 5-7
Section V
Figure 5-8.
Figure 5-6
Section V
Figure 5-6.
01768-2
Figure 5-7.
5-9
TM 11-6625-1541-15
Section V
Table 5-6 and Figure 5-8
Model 3400A
Table 5-6. Troubleshooting Procedure (Cont‘d)
Figure -5-8
5-10
Figure 6-3
Figure 5-8
Figure 5-13
Figure 5-9
01768-1
Model 3400A
TM 11-6625-1541-15
Section V
Table 5-6 and Figures 5-9 to 5-10
Table 5-6. Troubleshooting Procedure (Cont’d)
01768-2
Figure 5-9.
Figure 5-10.
Figure 5-11.
Figure 5-10
5-11
TM 11-6625-1541-15
Section V
Table 5-6 and Figure 5-11
Model 3400A
Table 5-6. Troubleshooting Procedure (Cont’d)
CHECK
PROCEDURE
Figure 5-11. Demodulator Output (Overdriven)
Investigate Modulator, Chopper Amplifier,
and Thermocouples. See Figures 5-12
through 5-17.
ACTION
Disconnect the base of Q604 from the chop-
a.
per assembly (V503). Insert a dc signal,
through a small resistor (1 K ), between
the base of Q604 and chassis ground, to provide-1.0v(+.15 v for 1/10 scale deflection). The meter should indicate full-scale
deflection. Trace the signal from the base
of Q604, through the thermocouples, back
to the modulator and through the chopper
amplifier.
Should a defective modulator be suspected,
b.
break the line between pin 13 (A6) and V501.
Apply a 10 mv dc signal through a 500 K resistor to V501. Check for a “chopped”
waveform at the junction of V501 and V502.
The modulated output should be proportional
to input dc level at pin 13.
Figure 5-12 describes a proper neon voltage
c.
waveform. Figure 5-13 describes an improperly firing neon. Note negative voltage dip
during conduction. Current variation
through neon, following voltage waveform,
causes noise as shown in Figure 5-8. For
proper chopper action, neon firing potential
(most negative point on waveform) is typically between 110 v and 120 v (never greater
than 130 v). Jitter occurring on front panel
meter may be seen at firing point or
extinguishing point.
d.
Check thermocouples and dc feedback from
C608. Check thermocouples for open circuit or ground.
5-12
01768-2
Model 3400A
Table 5-6. Troubleshooting Procedure
Figure 5-12
Figure 5-12.
TM 11-6625-1541-15
Section V
Table 5-6 and Figures 5-12 to 5-14
(Cont’d)
Figure 5-14.
Figure 5-13.
Figure 5-13
Prefixed 528
Figure 5-14
01768-2
5-13
TM 11-6625-1541-15
Section V Model 3400A
Table 5-6 and Figures 5-15 thru 5-17
Table 5-6.
Figure 5-15
Figure 5-15.
Figure 5-16
Figure 5-16.
Figure 5-17.
Figure 5-6.
Figure 5-17
5-14
01768-1
Model 3400A
TM 11-6625-1541-15
Section V
Table 5-6
Paragraphs 5-50 and 5-51
Table 5-6. Troubleshooting Procedure (Cont’d)
Figure 6-2
Figure 6-2
5-50. NEON SUBASSEMBLY,
0206, REPLAC
EMENT IN PHOTOCHOPPER AS-
PART NO. 1990SEMBLY, PART NO. 1990-0017.
5-51. To replace neon subassembly, proceed as
follows:
a. Remove chopper amplifier assembly (A6).
b. Disconnect all components and leads attached
to photochopper assembly at the A6 board. Note
location of connections for remounting of
chopper
assembly.
c. Remove the two screws on back of board and
remove the chopper assembly from the A6 board.
When removing the neon subassembly, note that
01768-2
the three wire cable grommet is off centered toward the end of the chopper block that has the
green wire connected to it.
d. Remove and discard the defective neon subassembly.
e. Install replacement neon subassembly (-hpPart No. 1990-0206). Insure replacement is orien-
tated correctly. See note in step 3 above.
f. Remount the chopper assembly. Reconnect
all components and leads disconnected in step
2.
g. Recalibrate the Model 3400A as outlined in the
Maintenance Section.
5-15
Model 3400A
TM 11-6625-1541-15
Section VI
Paragraphs 6-1 to 6-8
SECTION VI
CIRCUIT DIAGRAMS
6-1. INTRODUCTION.
6-2. This section contains the circuit diagrams
necessary for the operation and maintenance of the
Model 3400A RMS Voltmeter. Included are schematic
and parts location diagrams.
6-3. SCHEMATIC DIAGRAMS.
6-4. The schematic diagrams depict the circuits
contained within each assembly of the 3400A as well
as assembly interconnection. Main signal paths and
significant feedback paths are identified.
6-5. The schematic diagrams are arranged in
ascending order of assembly reference designation.
6-6. PARTS LOCATION DIAGRAMS.
6-7. The parts location diagrams show the physical
location of parts within an assembly. Parts are
identified-by reference designation. A parts location
diagram is included for each assembly which does not
have adequate silk screening of reference designations
6-6. The parts location diagrams are located on the
same figure as the schematic of the assembly.
01768-1
U.S. GOVERMENT PRINTING OFFICE: 1990 - 261-872/2063I
6-1
Model 3400A
TM 11-6625-1541-15
Section VI
Figure 6-1
01768-1
Figure 6-1. Input Attenuator A1, Impedance
Converter A2, and Second Attenuator A3
Schematic and Parts Location Diagram
6-3
TM11-6625-1541-15
Section VI
Figure 6-2
Figure 6-2. Video Amplifier A4 Schematic
and Parts Location Diagram
6-4
Model 3400A
TM 11-6625-1541-15
Section VI
Figure 6-3
01768-1
Figure 6-3. Modulator/Demodulator A5,
Chopper Amplifier A6, and Thermocouple
Pair (Part of A4) Schematic and Parts
Location Diagram
6-5
TM 11-6625-1541-15
Section VI
Figure 6-4
Figure 6-4. Power Supply A7
Schematic Diagram
6-6
Figure 6-4. Power Supply A7 Schematic
and Parts Location Diagram
TM 11-6625-1541-15
HEADQUARTERS
DEPARTMENT OF THE ARMY
WASHINGTON, D. C., 11 May 1967
TM 11-6625-1541-15 is published for the use of all concerned.
By Order of the Secretary of the Army:
HAROLD K. JOHNSON,
General, United States Army,
Official:
Chief of Staff.
KENNETH G. WICKHAM
Major General,
United States Army,
The Adjutant General.
Distribution:
Active Army:
USAMB (1)
USACDCEC (1)
UMCDCCEA (1)
USACDCCEA (Fr Huachuca) (1)
NG:
None.
USAR:
None.
Eighth USA (5)
SAAD (5)
TOAD (5)
LEAD (3)
For explanation of abbreviations used, see AR 320-50.
PIN :019316-000
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