Kenwood VT-187, VT-186, VT-185 Service Manual
2CH AC VOLTMETER
VT-185/VT-186/VT-187
SERVICE MANUAL
VT-187 only
FRONT PANEL
VT-185: (A63-0303-08)
VT-186: (A63-0304-08)
VT-187: (A63-0305-08)
KENWOOD TMI CORPORATION
© 1998-8/B51-1134-00 (K/K)
HANDLE : (K01-0564-08)
HANDLE COVER : (B09-0410-08)
PUSH KNOB
(K24-3015-08)
SIDE PANEL
(A13-2254-08)
ROTARY KNOB
(K21-0960-08)
RUBBER FOOT
(J02-0543-08)
VT-185/VT-186/VT-187
WARNING
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 (UNIT)......................................................................................................10
PARTS LIST (ELECTRICAL)........................................................................................11
SCHEMATIC DIAGRAM...............................................................................................16
P.C. BOARD .................................................................................................................26
2
Gain
Output voltage
Output resistance
Distortion
Signal to noise ratio
Frequency response
ITEMS
Meter Section
VT-185
Amplifier Section
VT-186 VT-187
Measurable voltage
dB
dBm
Error
Frequency response
Input impedance
Max. input voltage
Stability
Residual Voltage
Crosstalk Individual
Crosstolk Interlock
1mV to 300mV in ranges:
1, 3, 10, 30, 100, 300mV,
1 , 3, 10, 30, 100, 300V
full scal.
0.3mV to 100mV in 12 ranges :
0.3, 1, 3, 10, 30, 100, 300mV,
1, 3, 10, 30, 100V full scale.
-80 to +50dB (0dB=1V) -90 to +40dB (0dB=1V)
-80 to +52dBm
(0dBm=1mW at 600Ω)
-90 to +42dBm
(0dBm=1mW at 600Ω)
Within ±3% of full scale at 1kHz
±10% at 5Hz to 1MHz, ±5% at 10Hz to 500kHz,
±3% at 20Hz to 200kHz and ±2% at 30Hz to 100kHz
as response to 1KHz response.
10MΩ ±5%, with less than 45pF parallel capacitance.
500V(DC +AC peak)
1V to 300V range
100V(DC +AC peak)
1mV to 300mV range
500V(DC +AC peak) 1V to 100V range
100V(DC +AC peak) 0.3mV to 300mV range
Within ±0.5% of full scale for ±10% line voltage fluctuation
Less than 20 µV with input
shorted on 1mV range
Less than 30 µV with input shorted on 0.3mV range
Less than -50dB with other input terminated with 600Ω
Less than -80dB with other input terminated with 600Ω
Approx. 60dB Approx. 70dB
1Vrms (full scale) ±20%
600Ω ±20% at 1kHz
Less than 1% at full scale
(Rated by signal to noise ratio
in 0.3mV, 1mV and 1V range).
Less than 1% at full scale
(Rated by signal noise ratio in 1mV and 1V ranges)
Over 40dB at full scale. (Over 30dB at 0.3mV range)
Within ±3dB at 5Hz to 500kHz
Line voltage
Power consumption
Dimensions
W X H X D (mm)
Environmental
Power Supply Section
Coefficient
Temperature
Relative humidity
Maximum altitude
Overvoltage Category
Pollution Degree
±: 0.08%/°C
Within specifications : 10 to 40°C
Full operation : 0 to 50°C
Less than 80%
2000m
¿
2
100/120/220/230 Vac ±10% 50/60Hz
Max. 11W
128 (128) X 190 (210) X 239 (269)
Value in ( ) include protrusions
Approx. 3.2 kgApprox. 3.1 kg
Net Weight
1 pc.
CA-41p 2 pcs.
1 pc.
1 copy
1 pc.
EN55011 (1991) CLASS B
IEC801-2 (1991) 8kVAD
IEC801-3 (1984) 3V/M
IEC801-4 (1988)
Accessories
Power cable
Input cable
Replacement fuse
Instruction manual
Adjust driver
Regulatory Information (VT-186 only)
EMI
Immunity
7 The above specifications are subject to charge without noise.
VT-185/VT-186/VT-187
SPECIFICATIONS
3
VT-185/VT-186/VT-187
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 of 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 as 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 can be operated from 100 to 230V,
50/60Hz power source.
Use the following procedure to change from 100 to 230V
operation or vice versa.
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
–
4
VT-185/VT-186/VT-187
CIRCUIT DESCRIPTION
The voltage or sentence in parenthes is applicable in case of the "VT-185".
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 acts as an attenuator. The amount of
attenuation is switched in two steps by relay contacts:0dB
and -60dB.
2) Impedance Converter
A FET differential input Amplifier acts as an impedance converter with 0dB(10dB) gain, which converts the First Attenuator output signal to a sufficiently low impedance and feeds
of the Second Attenuator.
3) Second Attenuator
A resistance divider acts as an attenuator. The amount of
attenuation is switch in two steps by relay contacts:0dB and
-30dB.
4) Third Attenuator
A resistance divider network acts as an attenuator. The
amount of attenuation is switched in four steps by FET
switch:0dB, -10dB, -20dB, and -30dB.
5) Main Amplifier
A wideband, non-inverting differential amplifier acts as a
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 acts as an
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 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) 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.
10) CH1/CH2 Rotary Switch
A 12-contact rotary switch for setting a desired channel 1
and 2 measurable voltage range. This feeds a signal corresponding to the range into the Attenuator Control.
11) CH2 Rotary Switch
A 12-contact rotary switch for setting a desired channel 2
measurable voltage range. This feeds a signal corresponding to the range into the Attenuator Control.
12) CH2 Selector Switch
A Selector which is used to select either individual or interlocked range setting of channels 1 and 2.
13) CH1/CH2 Select Circuit
The range setting individual or interlocked selection circuit
are control by IC.
14) GND MODE Switch
A switch is used to disconnect the input negative circuits
from the casing ground.
15) Power ON/OFF
The power switch is designed to act on the secondary side
of the power transformer.
5
1st ATT
GND
OPEN
GND MODE
POWER
TRANSFORMER
POWER
ON/OFF
AC 100V/120V
220V/230V
50/60Hz
GND
INPUT-1
OUTPUT-1
2nd ATT 3rd ATT
+5V
VT-187 ONLY
VT-187 ONLY
ROTARY SW
MAIN AMP
OP-6RT-62
ABSOLUTE
MEAN
VALUE DET
IMPEDANCE
CONVERTER
ATT
CONTROL
OUTPUT
AMP
INPUT-2
INPUT-2
+5V
CH1/CH2
SELECT CIRCUIT
CH2
ROTARY SW
CH2
SELECTOR
+5V
CH1/CH2
ROTARY SW
6
VT-185/VT-186/VT-187
BLOCK DIAGRAM
VT-185/VT-186/VT-187
ADJUSTMENT
To obtain the best performance, periodically calibrate the
unit. Sometimes, only one mode need to 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 requires 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
Calibrator
CR Oscillator
Attenuator
Q-Meter
Distortion Meter
Insulation Meter
50Ω Termination
Model
DL-712
FC-756
CS-6010
5100B
AG-203
RA-920
4343B
885
SM-5
TA-57
Maker
KENWOOD
KENWOOD
KENWOOD
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
GND MODE
CH2 SELECTOR
POSITION
VT-185 : 300V
VT-186 : 100V
VT-187 : 100V
GND
OFF
7
VT-185/VT-186/VT-187
ADJUSTMENT
ITEM PROCEDUREADJUSTMENT POINT
300mV range VR102
Oscillator or calibrator
Main unit
REAR PANEL
OUT PUT
Oscilloscope
OUT
Oscillator
(Unless otherwise specified, the above connection should be used as to the following items.)
CH1/2 SWITCH : 300mV (VT-185)
CH2 SWITCH : 300mV (VT-185)
CH2 SELECTOR : OFF
1) Input 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
Calibrator
50Ω oscillator
0.3V (VT-186/VT-187)
0.3V (VT-186/VT-187)
1V range VR101
8
OK NG NG
CH1/2 SWITCH : 1V
CH2 SWITCH : 1V
CH2 SELECTOR : OFF
1) Input 1kHz (or 400 Hz), 1 Vrms sine wave, and set the pointer to 10.0 V of the 010 scale. Check that the variable range is less than 98% and more than 102%
with respect to 10.0 (full-scale).
2) Check that the operating, when CH2 SELECTOR is switched ON ( ) .
3) Waveforms shown on the oscilloscope shall not be deformed.
VT-185/VT-186/VT-187
0
3
10
ADJUSTMENT
ITEM
100 kHz TC101
frequency CH1/2 SWITCH : 1V
characteristics CH2 SWITCH : 1V
CH2 SELECTOR : OFF
1) Input a 1kHz (or 400 Hz), 1 Vrms sine wave, and adjust the oscillator output so
that the pointer of the set points at 9.0.
2) Adjust the TC so that the pointer points at 9.0 when the frequency is changed to
100 kHz while the oscillator output remains unchanged.
PROCEDUREADJUSTMENT POINT
Scale 9
Scale 0-10
Scale 0-3
9
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