Pioneer QuartzPLL PL-540 User manual

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c/Mlanual
Service
zPLL DIRECT DRIVE
STEREO TURNTABLE
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ar
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120V only
120V only
220V and 240V (switchable)
110V, 120V, 220V and 240V (switchable)
110V, 120V, 220V and 240V (switchable)
Canada model (without cartridge)
U.S.A. model (without cartridge)
Europe or Oceania model (without cartridge)
General export model (without cartridge)
U.S. Military model (within cartridge)
@ This service manual is applicable to the PL-540/KUT, KCT. For servicing of the other types
OQ PwNn a
please refer to the additional service manuals.
CONTENTS
SPECIFICATION i o6 a be Bok ae we wre eed area 3
PANEL FACILITIES AND OPERATION ..... 4
. DISASSEMBLY . 2.5.0.5... 5 ccc eee ee 6
PARTS LOCATION ................000. 7
. MECHANISM OPERATION AND ADJUSTMENT
5.1 Start of Performance ................ 8
5.2 Auto-return Detection ............... 8
5.3. Auto-return Operation .............. 9
5.4 Adjustment .................0004. 9
. CIRCUIT DESCRIPTIONS
6.1 Block Diagram .................0.. 11
6.2 Motor Operation .................. 13
6.3 Operation of the PD1003 IC
(Oscillator Stage) .............2.00. 15
6.4 Operation of the PA2004 IC
(Comparator Control) ............... 15
6.5 Operation of the PA2005 IC
fOriVe CORTON): notes ee ae oe ed ees, s 16
6.6 Trouble Shooting Chart .............. 20
6.7. Motor Adjustments ................. 22
7. EXPLODED VIEWS
DAN GAOINOE se eo ne ais oes ES 8 Bee 23
Tak’. “VONCBEMN espn: Sgn os OPS ae Sg eee Ge 24
1.3 - Botton Plate-../o-0 644.464 64 eon es 25
7.4 D.D. Motor(PXM-061)........0...0000. 26
TS - “Packing! o5 8a 3h eee fee eee de halt 27
. SCHEMATIC DIAGRAMS, P.C. BOARD
PATTERNS AND PARTS LIST
8.1 Schematic Diagram ................. 29
8.2 P.C. Board Connection Diagram ........ 31
8.3. Drive control Assembly (PWG-016) ...... 33
8.4 Oscillator Assembly (PWX-021)......... 34
8.5 Power Supply Assembly (PWR-042 KUT)
(PWR-040 KCT) .. 34
1. SPECIFICATION
Motor and Turntable
Drive SYStEM «. 5s. eee ko ae eee heen Direct-drive
MOlOl sone Ge onda eee See Quartz PLL Hall motor
Turntable Platter. . . 320mm diam. aluminum alloy die-cast
Moment of Inertia. .... 280kg-cm? (including platter mat)
Speeds: a4 lak Ducat aot tne we dae s 33-1/3 and 45rpm
Wow and Flutter........... Less than 0.025% (WRMS)
Signal-to-Noise Ratio. ....... More than 73dB (DIN-B)
(with Pioneer cartridge model PC-400)
Rotational Characteristics
Build-up Time ...... Within 120° rotation at 33-1/3rpm
Speed Deviation ................. Less than 0.002%
Speed vs. Load Characteristics... . Stable up to !50 grams
drag load
Speed Drift ....... Less than 0.00008%/h at 33-1/3rpm
Less than 0.00003%/degree temp. change at 33-1/3rpm
Tonearm
TVDG sae ame Se OA Static-balance type, S-shaped pipe arm
Effective Arm Length .................0.. 221mm
Overhand o6 <4 eo a eee a PEEPS Sse 15.5mm
Usable Cartridge Weight....... 4g (min.) to 10g (max.)
Subfunctions
Auto-return mechanism, Quick play mechanism,
PL-540
Anti-skating force control
Stylus pressure direct-readout counter weight, Cueing
device, Strobe light, Free stop hinges
Semiconductors
MSs Mh oh ete BN Uk SOS bode Si RACK BRA 3
LV aViSISUONSis 0.622 eS 2k Mia ew Ee Re eee a 3
OGG eso. Scr acces 8d 9b Soe bE ES ee ees 3
Aallelementse: 2 teen Be Oe eee es oe BG ee 3
Accessories
PPeAdaDtet satu bossa ete oe Ras ake Rah a |
SCO WON Y GF os ici svar so: co oe Gi Gl Grae Gen Bike doe ected 1
Cartridge mounting screws ...........000 000 ee 6
Cartridge mounting NNISh. 7. «50+ Cast ea swioees os 2
Cartridge mounting washers ...............00.. Z
Operating INsSttuClIONS.. << o04-545.0 wo-se uote egw S |
Miscellaneous
Power Requirements ............ AC 120V, 50, 60Hz
Power Consumption .....................04 8W
Dimensions ........... 440(W) x 145(H) x 365(D) mm
17-15/16(W) x 5-11/16(H) x 14-3/8(D)in.
Weient: date ars, wh BE eae tees 10kg/22Ib
NOTE:
Specifications and design subject to possible modification
without notice, due to improvements.

2. PANEL FACILITIES AND OPERATION
CONNECTIONS
The PL-540’s phono cables and ground lead are attached
to the rear panel of the turntable. The phono cable with
the white plug is for the left channel and the one with the
red plug is for the right channel. The thin wire with the
Y-shaped connector at the end is the ground lead. This
should be firmly connected to the ground terminal on the
amplifier.
The way in which the phono cables are attached will
depend on the type of cartridge used. Read the instruc-
tions in the booklet that comes with the cartridge as well
as the operating instructions of the amplifier, and connect
the phono cables properly.
Finally, plug the power cord into the AC outlet. Since
the auto-return mechanism may be engaged by vibration
during transportation, confirm its operation before play.
Move the tonearm over to near the center shaft. The turn-
table platter begins to rotate and the tonearm returns to
the arm rest. If the tonearm starts to move in the direc-
tion of the arm rest when moved manually, do not
forcibly move it toward the center shaft.
TONEARM
This tonearm is designed to apply the correct tracking
force to the cartridge and to keep this force at the precise
level for faithful tracking of the record grooves. It also
has the job of switching the power on to the turntable.
@ When the tonearm is moved from the arm rest to the
platter, the power comes on, the strobe lamp lights up,
and the platter rotates.
@ When the tonearm is returned to the arm rest, the
power to the turntable is cut off, the strobe light goes
off, and the platter stops rotating.
PLATTER/STROBOSCOPE
When the tonearm is moved and power is supplied to the
turntable, the platter will start rotating at the set rotation
speed.
When the turntable reaches its rated speed, the markings
around the side of the platter which constitute the strobo-
scope and which are illuminated by the strobe light
appear to stand still, indicating that the rated speed has
been reached.
PLATTER MAT.
This platter mat stabilizes the records and also absorbs
external vibration.
STROBE LIGHT
This light comes on when the tonearm moves away from
the arm rest toward the platter. It irradiates the strobo-
scope around the outside of the platter.
Ground
terminal AC outlet
Phono
input jacks
| PHONO
Phono cables ——
Power cord -~
EP ADAPTOR
Place this over the center shaft when you want to play a
record which has a large EP-type center hole.
Saati
DUST COVER
Keep this closed unless operating the controls or tonearm,
or
changing
over
records.
This
serves
to
keep
dust
from
adhering to the records during record play. When fully
opened and pulled straight up, this dust cover can be
removed from the cabinet.
ARM-ELEVATION
When the ARM-ELEVATION lever is operated, this will
move up or down. Its oil-damped mechanism and spring
ensure that the tonearm is raised and lowered smoothly.
ANTI-SKATE KNOB
This knob is used to cancel out the harmful skating force
which is generated during record play. .
For further details, see “ANTI-SKATING ADJUST-
MENT.”
ARM-ELEVATION LEVER
UP (A): When this lever is set to this position, the
tonearm will rise. Set it to UP before record
play and when you want to stop record play
while a track is being played or when you
want to change over to a different track.
DOWN ( ¥ ): When the lever is set to this position, the
tonearm will be lowered. If it is set to
DOWN for record play the tonearm will be
lowered onto the surface of the record, and
play will begin.
“< ry
or alt
Z ii
Q
“L A!
ar
{
ad
ee
Arm-elevation
lever
SPEED SELECT SWITCH
45 0... When this switch is depressed, the platter
will rotate at 45rpm. Depress for playing
45rpm records, singles or EP’s.
Oe
acest
When
this
switch
is
set
to
the
released
position,
the
platter
will
rotate
at
33rpm.
Release
for
playing
33-1/3rpm
records
like
LP's.
ARM REST
The arm rest supports the
tonearm. As illustrated in the
figure,
use
the
clamp
to
keep
the tonearm in place when
you are not playing records.
PL-540
OPERATION
ds
2.
gt
~l
Place the record to be played on the platter.
Set the SPEED select switch to the speed at
which the record is to be played.
. Set the ARM-ELEVATION lever to the UP
& position.
. Remove the stylus cover and release the arm
clamp.
. Hold the headshell by the finger lift and move
the stylus across the record to the track you
want played. The platter will begin to rotate.
. Set the ARM-ELEVATION lever to the DOWN
Vv position.
The stylus will descend slowly to the record
and play will begin.
. Adjust the volume and tone controls on the
amplifier to the preferred levels, and then sit
back and enjoy vour record.
. After the record has been played, the auto-
return mechanism is actuated and the tonearm
returns to the arm rest. At the same time, the
platter stops rotating and the power to the
turntable is turned off.
. Secure the tonearm to the arm rest with the
clamp and attach the stylus cover to protect the
stylus.
OPERATION PRECAUTIONS
Be careful not to make the turntable vibrate
while a record is playing, since this can result in
damage to the stylus and record.
Place only one record at a time on the platter.
If two or more records are stacked on the
platter, the stylus will not make proper contact
with the grooves, and this will impair the quality
of reproduction.
Do not disconnect the power cord while the
stylus is still in a record groove as this may result
in damage to the stylus and record.
Never obstruct the turntable with the hand while
it is rotating. This may cause damage.
Do not force the tonearm closer than 40mm to
the center shaft or away from the arm rest. If
this distance is exceeded, you may damage the
internal mechanisms and render automatic
operation ineffective.

3. DISASSEMBLY
1.
TURNTABLE
DISASSEMBLY
PROCEDURES
Control Panel
Disassemble
each
part
in
the
following
order.
1.
After
removing
the
turntable
platter,
undo
the
5 wood screws, and take off the cover.
2. Undo the 4 hexagonal wood screws.
3.
Undo
the
mechanical
base
mounting
screw.
4. Disconnect the PU cord connector.
5.
Unscrew
the
control
panel
from
the
mechanical
base.
6. Undo the push-type switch.
7. Disconnect the neon lamp tube.
8. Undo the lamp holder.
Tonearm
1. Undo 2 screws from the PU base plate.
2. Disconnect the PU leads from the PU base plate.
3. Loosen the PU plate screws, and then remove
PU plates A and B from the arm assembly.
4, Loosen the hexagonal screw securing the tone-
arm to the stand base, and then remove the arm.
va PU plate B a,
4. PARTS LOCATION
Cam unit
PYY-012
Power transformer
PT T-048 (KUT)
PTT-051 (KCT)
Power supply assembly
PWR-040 (KUT)
PWR-042 (KCT)
Rotor assembly
PXT-262
PL-540
D.D Motor
If the motor is to be removed. only remove it
after the control panel has been removed.
1. Disconnect all leads connected to the D.Dmotor
printed circuit board.
2. Undo the motor mounting screws.
Main weight assembly
PXA-708
Tone arm assembly
PPD-572
Head shell assembly
PXA-693
Drive control assembly
PWG-016

5. MECHANISM OPERATION
5.1 START OF PERFORMANCE
1. The tonearm is moved from the arm rest to
above the turntable.
2. Lever A, connected to the tonearm, unlocks
lever B, and the microswitch is turned ON
(Fig. 1).
3. When the microswitch is turned ON, the motor
is started and the turntable begins to rotate.
Microswitch
LeverB “NA
Fig. 1
5.2 AUTO-RETURN DETECTION
1. When the stylus nears the center shaft, lever A
contacts lever C (Fig. 2).
Lever A
Fig. 2
2. Lever C pushes plate A by an amount directly
proportional to the amount of movement of
the tonearm (Fig. 3).
Fig. 3
AND ADJUSTMENT
3. Plate B atop plate A is moved toward gear A
by the movement of plate A.
4. The front end of plate B moves approximately
0.1mm when the stylus is advanced 1mm
toward the center shaft by one revolution of
the record.
5. The tooth of gear A has the dimensional dif-
ference shown in Fig. 4-a.
6. Plate B is pushed back by this dimensional dif-
ference at a stylus movement of within 1mm
per revolution of the record.
7. When the stylus enters the lead-out groove in
the record at the end of the performance, it
is moved 4mm toward the center shaft by one
revolution of the record.
8. The end of plate B contacts the tooth of gear
A (Fig. 4-b).
9. Gear A and gear B are engaged, and gear B is
turned by rotation of the turntable.
Plate B
Fig. 4-a
Plate B
Fig. 4-b
5.3 AUTO-RETURN OPERATION
1. Gear B is rotated by detection of auto-return.
2. Lever D moves along the groove of gear B, and
the tone arm is lifted (Fig. 5).
f Arm lifted
Fig. 5
3. Lever A is pushed and the tonearm is returned
to the arm rest by lever D (Fig. 6).
Lever A
Fig. 6
4. When gear B has rotated one revolution, lever
D is returned to its original position.
dD. When lever D has returned to its original posi-
tion, lever B is pushed by lever A and the
microswitch is turned OFF (Fig. 7).
6. When the microswitch is turned OFF, the
motor is stopped, and the turntable also stops.
Lever B Microswitch
“NG
Fig. 7
PL-540
5.4 ADJUSTMENT
5.4.1 Auto-return Detection Position
1. Plate B contacts the tooth of gear A, the turn-
table is rotated, and the auto-retum detector is
reset.
Fig. 8
~
Adjust the adjusting screw so that plate B con-
tacts the tooth of gear A when the stylus has
reached a point 62mm from the center shaft.
Remove rubber cap
Soins
Fig. 9

5.4.2 Microswitch ON Timing
1s
10
Adjust
at
the
adjusting
point
shown
in
Fig.10-b
so
that
lever
A
and
lever
B
become
as
shown
in
Fig.
10-a
when
the
tonearm
is
fastened
to
the
arm
rest.
.
Adjust
the
adjusting
screw
(Fig.
10-c)
so
that
lever
B
and
the
microswitch
are
positioned
as
shown
in
Fig.
10-c
when
the
tonearm
is
fastened
to
the
arm
rest.
Since
this
adjustment
will
adversely
effect
the
auto-return
detection
position,
the
auto-
return
detection
position
must
be
readjusted.
Fig. 10-a
vi
-
!
i
H
Microswitch
Fig. 10-c

PL-540
6. CIRCUIT DESCRIPTIONS
6.1 BLOCK DIAGRAM
;
|
tL
Motor
Rotation
Ass‘y
|
5
Buffer — aie
Fy amplifier
converter
Waveform
rectification
i
—————————
=
St
sieaake
¢.
Ce
Position signal
Reverse rotation
<5
; .
13
76
formation
prevention
O-A
O
33.6
45
1
Frequency
divider
selector
II
14
a
|
Forward/reverse
TB
i
—O
direction
Comparator
control
.
"
:
discriminator
A
18
;
}
ir8
30Vv
|
19
Quick-stop
timin
s)
;
Frequency
divider
Mal
OSG
7
Voltage
stabilizer
|
_
|
z
pei
i]
’
t
GD
Mt
13
Motor
Drive
Ass’y
fe
.
eee
a
eee
ene
ART
7
A
4
PA2005
Oscillator
Ass’y
3 2
Lio
PO1003
12

6.2
MOTOR
OPERATION
3.
When
the
unit
is
switched
on,
the
output
voltages
of
the
respective
Hall
elements
will
be
as
shown
in
Fig.
20-a,
page
12.
4,
The
Hall
element
output
is
applied
to
the
—
Position
Signal
Combination
Circuit
contained
-.
figuration.
For
detection
of
the
platter
posi-
in
IC
PA-2005
and
utilized
to
control
the
cur-
~
os
rent
flowing
to
the
motor
drive
coils.
a
3
Hall
elements
are
mounted
at
40°
inter-
Por
Ride
ceuile.
sce
pagan
“Dave
Om
it 9?
3.
As
the
motor
rotates,
these
Hall
elements
ro
generate
an
AC
voltage
dependent
upon
ee
5.
The
output
from
the
Hall
elements
undergoes
strength
and
direction
of
the
magnetic
flux.
waveform
formation
in
the
Position
Signal
4.
The
bottom
side
of
the
rotor
magnet
possesses
Combination
circuit.
The
resulting
waveforms
200
magnetic
poles.
As
these
rotate
above
the
g
ae
showin
ik
mee
mae
;
tch
th
speed
detection
plate,
an
AC
voltage
is
generated
;
ese
composite
signals
are
used
to
switc
:
which
serves
as
the
speed
detection
signal
drive
current
in
such
a
way
that
each
motor
_The
inner
surface
of
the
rotor
magnet
possesses
winding
receives
the
proper
current
to
p
olarize
6
magnetic
poles.
As
shown
in
Fig.13
these
are
the
magnetic
poles
for
north,
south,
or
OFP
In
tilted
by
22.0°
relative
to
the
vertical
axis.
He
COTreCW
Sequence:
1 Motor Construction
1.
The
PXM-061
is
an
outer-rotor
brushless
DC
motor
with
6
poles
and
9
slots.
2.
Motor
windings
are
arranged
in
a
3-phase
Y
con-
Fig.
15-a
Fig.
15-e
or
In actual rotation, this happens as follows.
7.
As
the
pole
of
coil
La
becomes
a
south
pole,
that
of
Lg
becomes
north,
and
Leg,
neutral.
8.
Repulsion
between
the
S
pole
at
La
and
the
rotor
S
pole,
and
attraction
between
the
Lg
N
pole
and
the
rotor
S
pole
exert
a
propulsive
force
on
the
rotor.
.
9.
As
the
rotor
turns
through
20°
of
arc,
the
Fig.
15-b
Fig.
15-f
output
from
the
Hall
elements
changes.
10.
Lg
now
enters
OFF
state,
Le
becomes
a
N
pole,
and
L,
aS
pole.
Speed
Detection
Plate
Hall
Element
11.
The
Le
N
pole
now
attracts
the
rotor
S
pole,
Fig.
12
and
the
La
S
pole
attracts
the
rotor
N
pole.
Rotation continues.
12.
Correspondences
between
rotor
positions
and
coil
polarities
are
shown
in
Fig.
15,
a-f.
3. Speed Detection Section
1.The
speed
detection
plate
has
one
rows
of
“detection
patterns.”’
2.
The
bottom
surface
of
the
rotor
is
magnetized
with
200
magnetic
poles,
and
these
rotate
at
a
short
distance
above
the
speed
detection
plate.
3.
The
output
voltage
from
the
detection
patterns
has
a
frequency
of
55.5Hz
at
33-1/3
rpm,
and
of
75Hz
at
45
rpm.
S
>
Fig.
15-c
4.
The
signal
is
supplied
to
IC
PA2004.
Fig. 13
2. Principle of Motor Rotation
1. Let us assume that the motor is at standstill,
in the position shown in Fig. 3.
2. In this position, Hall element Ha is located
next to a borderline between south and north
poles,
Hg
next
to
a
south
pole,
and
H¢
next
to
Fig.
15-d
@ rortlh, pole.
Fig. 14

6.3
OPERATION
OF
THE
PD1003
IC
(OSCILLATOR
STAGE)
_
Once
the
power
supply
is
turned
on,
the
quartz
crystal
oscillator
generates
a
6144kHz
signal.
The
frequency
of
this
signal
is
reduced
to
1.5kHz
(1/4096
division)
by
frequency
divider
I.
Part
of
the
resultant
signal
is
passed
via
the
x’tal/RC
switching
circuit
and
applied
to
frequency
divider
II.
The
other
part
of
the
signal
is
applied
to
frequency
divider
selector
II.
.The
1.5kHz
signal
applied
to
frequency
divider
Il
is
further
divided
into
a
750Hz
signal,
and
applied
to
frequency
divider
selector
I
where
the
signals
are
converted
into
sampling
pulses
for
phase
comparison
purposes
in
PA2004.
33rpm =—s-_ 27.78 Hz
45rpm =: 387.5 Hz
(In both cases, the pulse width is 0.667ms).
. Frequency divider selector II converts signals
from frequency divider I into pulse signals for
the stroboscope lamp drive circuit.
33rpm = 555.5Hz
45rpm_~==75.0Hz
(In both cases, the pulse width is again 0.667ms).
6.4 OPERATION OF THE PA2004 IC
(COMPARATOR CONTROL)
. Signals from the frequency generator in the
motor rotation ass’y are changed into 50% duty
square wave signals by the waveform rectifier.
The frequencies at this stage are thus,
338rpm =—s«555.5 5 Hz
45rpm = 75Hz
. Part of the output is divided by % in the FF
circuit, and subsequently applied to the FV
converter circuit along with the other part of
the output formed in step 1 above, thereby
forming the FV converter gate pulse signals.
. The output from the FV converter is applied to
buffer amplifiers I and II.
. The buffer amplifier I output is compared with
the reference voltage in buffer amplifier III, and
then applied to the output compose circuit.
. Phase comparison of the sampling pulses from
the PD1003 IC with the FV converter output
occurs in buffer amplifier II, with the resultant
output being applied to buffer amplifier IV.
. The output from buffer amplifier IV is also
applied to the output compose circuit.
. This output compose circuit consists of a low-
pass filter (cut-off frequency 23Hz, cut-off slope
—6dB/oct.) which serves to eliminate the carrier
component in the output of buffer amplifier II
(phase comparison).
. This final output signal is then passed onto the
comparator control stage of the PA2005 IC for
comparison with the reference voltage.
6.5 OPERATION OF THE PA2005 IC
(DRIVE CONTROL)
e Stroboscope Pulse Circuit
Me
The platter has only a single row of stroboscopic
markings. Switchover for 45 and 33 rpm is ef-
fected by changing the frequency of the pulse
to the stroboscopic lamp.
.From the Frequency Divider Selector I, a fre-
quency of either 75Hz (for 45 rpm, representing
1/80 of 6000Hz) or 55.5Hz (for 33 rpm, repre-
senting 1/108) is obtained and supplied to the
transistor that drives the stroboscopic lamp.
@ Reverse Rotation Prevention
. PXM-061 operates indiscriminately in regard to
the direction of rotation. If the platter is turned
slowly in the reverse direction by hand, a for-
ward torque will be applied until the platter
stops, reverses its rotation and reaches rated
speed in the proper direction.
. If, however, the rotational speed in the reverse
direction is in excess of 33 or 45 rpm, the
Forward/Reverse Command Block may ‘“mis-
read” this as simply excessive speed (“‘overrun’”’)
and apply a reverse torque until rated speed is
attained.
. This reverse torque will further accelerate the
turntable rotation in the reverse direction. This
is known as ‘“‘reverse run-away.”’
.To prevent this from happening, a Reverse
Rotation Prevention circuit has been included.
_This Reverse Rotation Prevention circuit con-
sists of two flip-flops and AND gates See Fig. 12.
.The input for this circuit is derived from the
Hall element position detection signals processed
in the Reverse Rotation Prevention circuit.
. As long as the platter is rotating in the proper
direction, this pulse enters in the order B — A —
C, and no “reverse”? command is generated.
_If, however, the platter rotates in the reverse
direction, the pulse order becomes A — B — C,
and a corrective command is given to the For-
ward/Reverse Command Circuit.
AND
©
Output
Forced Forward
Rotation at 0 output
Fig. 16
Truth table
@ Comparator Control and Forward/Reverse Com-
1.
V18... Voltage at pin (18)
mand Circuit
Two inputs are supplied to the Control Com-
parator: a) a 4V reference voltage from the volt-
age stabilizer; and b) the output from the active
filters, which serves as the detection signal.
_If the tumtable rotates faster than rated speed,
the detection signal is higher than the 4V
reference.
.When this happens, the Comparator Control
sends a command to the Forward/Reverse Com-
mand Circuit, telling it to apply a reverse torque
to the motor to slow it down.
. Conversely, if turntable rotation is below rated
speed, the detection signal voltage will be below
the 4V reference.
.In this case, the Comparator Control indicates
to the Forward/Reverse Command Circuit that
forward torque must be applied to the motor to
accelerate it.
< Si
Area of of Area of &
Sy, reverse = forward xO
oy, torque 6 torque Oo
% rs) @
S RS
I Vv
e)
O
¢ Input voltage differential between
pins (18) and (19)
V19... Voltage at pin (19)
Fig. 17
1€

® Drive Circuit
1. The signals employed in the switching of Q2 ~
Q7 in Fig.18 are generated by 3 Hall elements,
and applied to terminals a, b, and c via the
position signal formation circuit.
2.
The
phase
of
these
step
waveform
Signals
is
displaced
by
120°
from
each
other.
3.
When
the
step
waveform
signals
at
position
I
in
Fig.
19-a
are
applied
to
the
drive
circuit
terminals
a,
b,
and
c,
the
potential
at
terminal
a
will
be
lowered,
resulting
in
Q2
being
turned
on.
The
potential
at
terminal
b
will
be
raised,
resulting
in
Q6
being
turned
on,
but
the
potential
at
terminal
c
will
remain
at
the
reference
level
voltage
(the
bias
settings
for
Q4
and
Q7
have
been
designed
to
prevent
these
2
transistors
from
operating
when
a
reference
level
voltage
is
applied).
4.
Vcc
will
thus
be
applied
across
the
Q2
—
coil
La
—
coil
Lg
—
(2)
—
Q6
route,
thereby
pro-
ducing
an
S
polarity
in
La,
and
an
N
polarity
in
Lp.
Control o
i
|
|
5.
Once
the
magnetic
filed
is
generated,
the
rotor
will
commence
to
rotate.
After
the
rotor
turns
through
20°,
the
signals
at
position
II
in
Fig.19-b
will
be
applied
to
terminals
a,
b,
and
c,
thereby
resulting
in
a
change
in
the
flow
routes
of
the
drive
currents.
After
the
rotor
turns
through
another
20°,
the
signals
shown
at
position
III
in
Fig.
19-c
will
be
applied,
again
resulting
in
changes
in
flow
routes
of
the
drive
currents.
For
every
20°
that
the
rotor
turns
through,
the
flow
routes
for
the
drive
currents
will
change
as
shown
in
Figs.
19-d,
19-e,
and
19-f,
finally
returning
to
the
routes
shown
in
Fig.19-a
again.
6.
A
control
voltage
generated
by
the
forward/
reverse
direction
discriminator
indicator
circuit
is
applied
to
the
control
input
terminal,
thereby
controlling
the
flow
of
current
in
the
coils.
) mv)
{
a o— |
= seleak
b 0- x :
Fig. 18
Rss:
Fig. 19-a
ICC
!
a
eee
QO
ok.
:
|
|
2
=O
We
|)
“sa,
ag
Saat
nit
pa
Dh aa =
4
4
7
oo
-«
Sharer:
,
Control
|
a
aio
ee
es
;
4
pk.
input
—
He
Se
GND
;
Fig. 19-b
wows voc
Fig. 19-c
Controt
input
Fig. 19-f