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CIRCUIT DESCRIPTION
VR20 and VR21:
I1C13 offset adjustment
VR22: Adjuster for 1 Vdc output
Power supply circuit
The AC 20 V voltage from the power transformer is recti-
fied by diode D24 into DC + 20 V. It is then regulated by the
stabilizer circuit consisting of IC4, Q101
and Q102. This
stabilizer circuit outputs DC + 15 V. This DC voltage is ad-
ded to amplifier units and some blocks of the counter unit.
This circuit uses the + 5 V voltage from the counter unit as
the reference voltage. Variable resistor VR23 is adjusted so
that — 15 V can be generated.
3. FREQUENCY COUNTER CIRCUIT
(COUNTER UNIT)
Frequency counter circuit
The frequency of the crystal oscillator employed in this unit
is 10.080 MHz. The output from the crystal oscillator is first
transmitted to transistor Q201 and then to the Q202 buffer
transistor. It is then sent to the !C201
and divided by four
into 2.5200 MHz. Use another frequency counter to meas-
ure the signal at test point TP201.
If its frequency is not
2.5200 MHz,
adjust
TC201
so
that
it can
reach
2.5200 MHz.
This signal (2.5200 MHz signal) is input to the divider cir-
cuit consisting of IC202, 1C210 and 1C211 and then divid-
ed by eight hundred into a 3.15 kHz-squarewave signal. It
is also input to the divider circuit consisting of 1C202 to
1C206 and then divided by 840 into 3.00 kHz squarewave
signal.
One of the squarewave signals described above is selected
by the OSC select switch of the X69-1000-00 (S2) and then
input to the 1C212. It then moves onto a band pass filter
through the low-impedance Q208 emitter follower output
circuit. The band pass filter consists of three coils (L201 to
L203) and four capacitors (C212 to C215).
The bandwidth of the filter is 3.0+0.5 kHz (2.95 kHz to
3.5 kHz). Therefore, it can convert the squarewave signal
with a frequency of 3 kHz or 3.15 kHz into sinewave sig-
nals with a distortion rate of less than 1.0%.
The sinewave signals are transferred to the Q209 buffer am-
plifier and then need to be adjusted by variable resistor
VR201
into
200 mVrms
output
signals
(with
no
load
resistance). These output signals are transmitted to an ex-
ternal
circuit as the OSC
OUT
signals. Their output im-
pedance is 600 ohm.
The output from the IC206 (1/840 divider) is input to the
1/300 divider circuit consisting of IC207, IC208 and IC209
and then divided into a 10 Hz signal. This signal is used as
a time base for the counter unit.
The 10 Vac output (50/60 Hz) from power transformer T1
is input to the 1/5 divider (IC214:50 Hz) or 1/6 divider
(IC215:60 Hz) and then divided into a 10Hz signal. This sig-
nal is synchronized with the power supply signal (50/60 Hz).
One of the two 10-Hz signals described above that is gener-
ated based on the power supply signal(50/60 Hz) or crystal
oscillation (10.08 MHz) is selected by select switch S6.
Select switch S8a is provided to select a gate time from 1
second and 0.1 second.
If the 1-second gate time is selected, the selected 10-Hz sig-
nal is transferred to the two divider circuits (IC216 and
1C208) and then divided by 20 into a 1-second gate control
signal.
If the 0.1-second gate time is selected, the selected 10-Hz
signal is transferred to the 1/2 divider circuit directly and then
converted into a 0.1-second gate control signal. These con-
trol signals are input to the pulse generation circuits (1C217
and IC218). The IC217 generates latch timing pulses from
the control signals and then outputs them to the IC222 while
the IC218 generates reset pulses from the signals and then
outputs them to the IC222.
The output signal from the Schmitt trigger circuit of the am-
plifier unit is input to the 1C224 gate circuit through the 0203
and IC224 buffer. It is then transmitted to the IC222 as a
counter clock signal after it is mixed with the 1-second or
0.1-second gate control signal.
The IC222 is a 4-digit decode counter. Its B.C.D output is
input to the 1C221 and then decoded into 7-segment LED
drive signals. These decoded signals are input to the cathode
terminals of the 7-segment LEDs. The output from the IC222
decode
counter
is input to the anode
terminals
of the
7-segment LEDs through the switching circuit consisting of
the IC223 and transistors Q204 to Q207.
The 1C222 4-digit decode counter outputs an overflow sig-
nal if the gate time is set to 1 second and the signal higher
than '9.999 kHz' is input. This overflow signal is transmit-
ted to the 1C216, IC220
and then {C219, and finally turns the level monitor LED ON
and OFF.
Power supply circuit
The AC 10V output from power transformer T1 is rectified
by diode D202 and then input to the stabilizer circuit con-
sisting of IC225 and Q103. The stabilizer circuit regulates
the D202 output and then generates +5 V. This +5 V vol-
tage is added to each TTL circuit. It is also added to the
stabilizer circuit of the amplifier unit and used as the refer-
ence voltage.
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