Kenwood VT-181E, VT-181 Service Manual
AC VOLTMETER
VT-181/VT-181E
SERVICE MANUAL
HANDLE : (K01-0564-08)
HANDLE COVER : (B09-0410-08)
FRONT PANEL
VT-181 : (A63-0301-08)
VT-181E : (A63-0316-08)
KENWOOD TMI CORPORATION
© 1998-4/B51-1132-00 (K/K)
SIDE FRAME
(A13-2254-08)
PUSH KNOB
(K24-3015-08)
KNOB
(K21-0959-08)
RORARY KNOB
(K21-0961-08)
RUBBER FOOT
(J02-0543-08)
VT-181/VT-181E
The following instructions are for use by qualified personnel only. To avoid electric shock,
do not perform any servicing other than contained in the operating instructions unless you
are qualified to do so.
CONTENTS
SPECIFICATIONS..........................................................................................................3
SAFETY..........................................................................................................................4
CIRCUIT DESCRIPTION................................................................................................5
BLOCK DIAGRAM..........................................................................................................6
ADJUSTMENT................................................................................................................7
PARTS LIST....................................................................................................................9
PARTS LIST (ELECTRICAL)........................................................................................10
SCHEMATIC DIAGRAM...............................................................................................15
P.C. BOARD .................................................................................................................21
WARNING
2
VT-181/VT-181E
SPECIFICATIONS
Meter Section
Measurable Voltage
dB
dBm
Error
Frequency response
Input impedance
Durable input voltage
Stability
Residual voltage Less than 20uV with input shorted on 1mV range
500V (DC +AC peak) 1V to 300V range
100V (DC +AC peak) 1mV to 300mV range
Amplifier Section
Gain
Output voltage
Output resistance
Frequency response
Distortion
Less than 1% at full scale (Rated by signal-noise
ratio in 1mV and 1V range)
1mV to 300mV in 12 ranges:1,3,
10,30,100,300mV,1,3,10,30,
100,300V full scale.
-80 to +50dB(0dB=1V)
-80 to +52dBm(0dBm=1mW at 600Ω)
Within ±3% of full scale at 1kHz
±10% at 5Hz to 1Mhz, ±5% at 10Hz to 500kHz and
±2% at 20Hz to 100kHz as reference to 1kHz response.
10MΩ ±5%, with less than 50pF parallel capacitance.
Within ±0.5% of full scale for ±10 line voltage fluctuation
60dB ±1dB(Approx.70dB)
1Vrms ±20%
600Ω±20% at 1kHz
Within±3dB at 5Hz to 500kHz
VT-181EVT-181Item
0.3mV to 100mV in 12 ranges:0.3,
1,3,10,30,100,300mV,1,3,10,
30,100V full scale.
-90 to +40dB(0dB=1V)
-90 to +42dBm(0dBm=1mW at 600Ω)
500V (DC +AC peak) 1V to 300mV range
100V (DC +AC peak) 0.3mV to 300mV range
Less than 30uV with input shorted on 0.3mV
range
Less than 1% at full scale (Rated by signalnoise ratio in 0.3mV,1mV and 1V ranges)
Signal to noise ratio
Environmental
Within specifications
temp./ hum.range
Full operation temp./
hum.range
Indoor Use Only Altitude up to 2000m OVERVOLTAGE CATEGORY¿ POLLUTION DEGREE2
Power Supply Section
Line voltage
Power consumption
Dimensions
WXHXD(mm)
Net Weight
Accessories
Power cable
Input cable
Replacement fuse
Instruction manual
Adjust driver
Over 40dB at full scale
10 to 40˚C / 80% RH or less
100/120/220/230/ Vac ±10% 50/60Hz
128(128)X190(210)X239(259)
Value in ( ) include protrusions
Over 30dB at 0.3mV range
0 to 50˚C / 80% RH or less
Max.6.9W
2.8kg
1pc
CA-41p 1pc
1pc
1copy
1pc
3
VT-181/VT-181E
SAFETY
SAFETY
Before connecting the instrument to a power source, carefully read the following information, then verify that the
proper power cord is used and the proper line fuse is
installed for power source. The specified voltage is shown
on the rear panel. If the power cord is not applied for
specified voltage, there is always a certain amount of danger from electric shock.
Line voltage
This instrument operates using ac-power input voltages
that 100/120/220/230 V at frequencies from 50 Hz to
60Hz.
Power cord
The ground wire of the 3-wire ac power plug places the
chassis and housing of the instrument at earth ground. Do
not attempt to defeat the ground wire connection or float
the instrument ; to do so may pose a great safety hazard.
The appropriate power cord is supplied by an option that
is specified when the instrument is ordered.
The optional power cords are shown as follows in Fig.1
Plug configuration power cord and plug type
North American
120 volt/60 Hz
Rated 15 amp
(12 amp max ; NEC)
Line fuse
The fuse holder is located on the rear panel and contains
the line fuse. Verify that the proper fuse is installed by
replacing the line fuse.
Voltage conversion
This instrument may be operated from either a 100 to
230V, 50/60Hz power source.
Use the following procedure to change from 100 to 230V
operation or vice verse.
1. Remove the fuse holder.
2. Replace fuse F1 with a fuse of appropriate value.
3. Reinsert it for appropriate voltage range.
4. When performing the reinsertion of fuse holder for the
voltage conversion, the appropriate power cord should
be used. (See fig.1)
Factory installed
instrument fuse
0.2A, 250V
slow blow
5x20mm
Line cord
plug fuse
None
Parts No. for
power cord
E30-1983-08
Universal Europe
230 volt/50 Hz
Rated 16 amp
U.K.
230 volt/50 Hz
Rated 5 amp
Australian
240 volt/50 Hz
Rated 10 amp
North American
240 volt/60 Hz
Rated 15 amp
(12 amp max ; NEC)
Switzerland
230 volt/50Hz
Rated 10 amp
Fig.1 Power Input Voltage Configuration
0.1A, 250V
slow blow
5x20 mm
0.1A, 250V
slow blow
5x20 mm
0.1A, 250V
slow blow
5x20 mm
0.2A, 250V
slow blow
5x20mm
0.3A, 250V
slow blow
5x20 mm
None
5A
Type C
None
None
None
E30-1982-08
E30-1985-08
E30-1986-08
Ñ
Ñ
4
VT-181/VT-181E
CIRCUIT DESCRIPTION
The voltage or sentence in parenthes is applicable in case of the "VT-181E".
In studying the operation of each circuit in voltmeter please refer to "BLOCK DIAGRAM".
General
A Signal voltage to be measured, which is input from the
INPUT connector, is passed through the First Attenuator
and is converted to a low impedance by the Impedance
Convertor. The impedance-converted signal is normalized,
or further attenuated in proportion to 1mVrms fullscale value
through the Second and Third Attenuator. The normalized
signal is magnified 20-fold by the Main Amplifier and is fed
to the Output Amplifier and the Absolute-Mean Value Detector.
The Output Amplifier magnifies the signal 50-fold and feeds
to the OUTPUT connector. The Absolute-Mean Value
Detector converts the signal from the Main Amplifier to DC
current in proportion to the absolute mean value. The converted signal activates the Meter.
The Attenuator Control encodes the signal led from the
RANGE selector to generate an Attenuator Control signal.
This signal controls the First, Second and Third attenuator to
set the sensitivity corresponding to each range.
The Power Supply feeds to the functional circuit ±5V DC
voltages stabilized by its IC regulator.
Description of Functional Circuit
1) First Attenuator
A potential divider act as a attenuator. The amount of attenuation is switched in tow steps by relay contacts:0dB and 60dB.
2) Impedance Converter
A FET differential input Amplifier act as a impedance converter with 0dB(10dB) gain. Which converts the First Attenuator output signal to a sufficiently low impedance and feeds
of the Second Attenuator.
5) Main Amplifier
A wideband,non-inverting differential amplifier act as the
main amplifier. Which has high input impedance,low output
impedance and 20-fold gain. This output signal level is
20mVrms for the fullscale read on the Meter.
6) Output Amplifier
A wideband,non-inverting differential amplifier act as a output amplifier. Which has 50-fold gain and 600Ω output
impedance. The output signal level is 1Vrms for fullscale
read on the Meter,and works stable even for capacitive
loads.
7) Absolute-Mean Value Detector
An absolute-mean value detector comprised of a high
through-rate and high gain amplifier. Which has a very good
linearity by negative feedback from the current flowing
through the Meter load. In switching, this provides a sufficiently wide frequency band so that the high frequency
phase compensation circuit is reset.
8) Attenuator Control
A logic control circuit comprised of a diode matrix and output
buffer transistors. This encodes a 12-bit signal from the
RANGE selector switch to 6-bit signals,which control the
First,Second and Third Attenuator. The remote control connector is connected to this circuit.
9) Rotary Switch
A 12 contacts rotary switch which design the operation
range. For different range,different attenuation ratio are activated.
10) Gain Control
To using the dB scale to measure relative voltage, you may
get a reference reading by change the gain control. (relative
ref.) Which capable to vary 0 to 10dB.
3) Second Attenuator
A resistance divider act as a attenuator. The amount of
attenuation is switch in two steps by relay contacts:0dB and
-30dB.
4) Third Attenuator
A resistance divider network act as a attenuator. The
amount of attenuation is switched in four steps by FET
switch:0dB,-10dB,-20dB,and -30dB.
11) Power Supply
The power source circuit supply±5V DC from the AC input.
Which contain a silicon diode bridge for full-wave rectification,high-capacitance electrolytic capacitors for
smoothing,and an IC regulator stabilization.
5
6
VT-181/VT-181E
INPUT
CH1. PC BOARD OUTPUT-1
1st ATT
ROTARY SW
AC 100V/120V/220V/230V
50/60Hz
IMPEDANCE
CONVERTER
POWER
TRANSFORMER
2nd ATT
ATT
CONTROL
POWER ON/OFF
3rd ATT
MAIN AMP
POWER SUPPLY
OUTPUT AMP
GAIN
CONTROL
RELATIVE REF
METER
ABSOLUTE
MEAN
VALUE DET
DC5V
GND
DC-5V
BLOCK DIAGRAM
VT-181/VT-181E
ADJUSTMENT
To obtain the best performance, periodically calibrate the
unit. Sometimes, only one mode need be calibrated, while at
other times, all modes should be calibrated. When one
mode is calibrated, it must be noted that the other modes
may be affected. When calibrating all modes, perform the
calibration in the specified sequence.
The following calibration required an accurate measuring
instrument and an insulated adjusting flat blade screwdriver.
If they are not available, contact your dealer. For optimum
adjustment, turn the power on and warm up the scope sufficiently (more than 30 minutes) before starting.
Before calibrating the unit, check the power supply voltage.
TEST EQUIPMENT REQUIRED
The following instrument or their equivalent should be used
for making adjustment.
Test Equipment
Digital Multimeter
Frequency Counter
Oscilloscope
ITEM PROCEDUREADJUSTMENT POINT
300mV range VR102
Model
DL-712
FC-756
CS-6010
Maker
KENWOOD
KENWOOD
KENWOOD
Test Equipment
Calibrator
CR Oscillator
Attenuator
Q-Meter
Distortion Meter
Insulation Meter
50Ω Termination
Model
5100B
AG-203
RA-920
4343B
885
SM-5
TA-57
Maker
FLUKE
KENWOOD
KENWOOD
YHP
Shibasoku
TOA
KENWOOD
PREPARATION FOR ADJUSTMENT
Control Settings
The control settings listed below must be used for each
adjustment procedure.
Exceptions to these settings will be noted as they occur.
After completing a adjustment, return the controls to the following settings.
NAME OF KNOBS
RANGE
RELATIVE REF
Main unit
POSITION
VT-181 : 300V
VT-181E : 100V
CAL
Oscillator or calibrator
OUT
Oscillator
(Unless otherwise specified, the above connection should be used as to the following items.)
RANGE: 300 mV
1) Input a 1 kHz (or 400 Hz), 300 mVrms sine wave, and set the pointer to 3.0 of the
0-3 scale. Check that the variable range is less than 98% and more than 102%
with respect to 3.0 (full-scale).
2) Waveforms shown on the oscilloscope shall not be deformed.
OUT
IN
Calibrator
CAL
OUT
50Ω oscillator
Oscilloscope
OK NG NG
7
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