Dual 621 - Pitch Control and Speed Setting; Pitch Control Operation and Adjustment; Stroboscope Speed Verification

3. Unsolder
connecting leads to rotary switch (5)
and the gene-
rator. Open twists of holding angle (150) with flat pliers. Lift
off motor
electronic (152). Remove machine screw (151)
and
holding angle
(150).
4. Loosen
threaded
pins
(15)
and remove
platter cone
(14).
Remove the three
screws (148). Lift off
motor mechanics
(149).
5. Put platter
cone (14) on new motor
mechanics and fix it. Fix
new motor mechanics with the three screws
(148).
Fix
holding
angle (150) with screws
(151). Insert motor
electronics
(152) and twist holding pieces.
Solder on resp. plug connecting leads (Fig. 4).
Push cover on power part and fix it with screws (112).
6. With the unit in normal position connect it to the power line
Switch on unit and check power consumption when
opera-
ting:
220 V/50 Hz
approx. 15 mA
110 V/60 Hz approx. 25
mA
Check nominal
speeds. If
necessary,
readjust as described
below.
Setting nominal speeds
With
knob (7)
bring the fine speed control
(129/R
19) into
center position. With controls (R 8) and (19
9) on
the motor elec-
tronic system adjust nominal speeds.
Control (13 8) is used for
33 1/3 rpm, R 9 for 45 rpm. Check with strobe disk.
Changeover to 78 rpm
nominal speed
Instead of 45 rpm the
Dual 621 can
be
changed to
a
nominal
speed of 78 rpm.
To change the speed bring the fine
speed
control
(129/R 19) in
center position
using knob (7). Using
control R 9 on the
motor
electronics board (172)
adjust for 78 rpm.
Check with strobe
disk.
Stroboscope
Accurate
setting of the
platter speeds 33 1/3
and 45 rpm can
be
checked during play
with the aid of the
stroboscope.
When the platter (4) is rotating at
exactly 33 1/3
or 45
rpm the
lines
of the
stroboscope appear to stand
still. If the lines
move
in
the direction of
rotation of the platter,
the platter speed is too
high. If the lines
move backwards, the
platter is rotating
more
slowly than the
nominal speed.
Adjustment of platter speeds
33 1/3 and 45 rpm can make
with the "pitch" control (7).
Strobe markings are provided
on the outer edge of
the platter
for 50 and 60 Hz line
frequencies.
To replace glow lamp (157) remove
machine screws (160)
and
remove
strobe cover (156).
lt can happen that the
stroboscope lines appear to
move slightly
although the exact speed setting with
stroboscope stationary has
not been
altered. This apparent
contradiction is explained by the
fact that the
electronic central drive motor
operates fully inde-
pendently of line
frequency whilst the only relatively
accurate
line frequency of the AC
current supply is used for
speed
measurement
with the light stroboscope. The
constantly detec-
table fluctuations of line frequency by ± 0.2 % according to the
information of
the electricity supply
companies
brief frequency
fluctuations up to 1 % are
possible — only effect the
stroboscope
indication and can cause the
lines to "wander" although the
platter speed is as
constant and absolutely
accurate as before.
P itch
Control
Each of the two standard speeds 33 1/3 and 45 rpm (78 rpm)
can be varied by
about 10 %. The variable
speed control
1129/
R 19) located in the voltage divider is adjusted by turning the
pitch control knob (7). By this the differential amplifier is
altered and the motor speed accordingly.
Fig. 6
153
144
156
157
159
160
Fig. 7
Netztrafo
Mains
transformer
Transformateur de
ffi
seaLi
C52
fIJ
e
63 mA mT 0 220V
110V
Motor
Motor
Moteur
Glimmlampe
Glim
lamp
Lampe ä
effluves