Pioneer pl-530 Service Manual page 32

l-
l--
t:
,t
I
,t
r
turning at the correct speed (revs), this circuit is
balanced. If for any reason the speed of rotation
of the rotor exceeds the proper value, the voltage
generated in each drive coil will increase.
This causes the potential on the base of Qrr, Qru
to rises, and the potential on the bases of Q1a rises.
As the potential on the base of Qra rises, the
collector current drops and this reduces the poten-
tial on the base(s) of Q,r. This results in a reduc-
tion in the current flowing through Qr3, and a rise
in the potential on the emitter(s) of Qe (Qr, Q'z ),
so that the collector current(s) of Qa (Qr, Q,z)
drop. If the collector current drops, the field
strength of the drive coil also drops, the rotor
speed drops, and it returns to the correct speed of
rotation.
On the other hand, if the rate of rotation of the
rotor drops below its proper value, the process is
precisely the reverse of the above: the voltage
across each drive coil drop.s, and the base potential
of Qts drops. This causes the collector current of
Qto to increase, and the current(s) through Qr3
also rise. As the collector current(s) of Q'r increase,
the emitter potential(s) on Qo (Qa, Q'z ) drop, the
collector current(s) rise, the magnetic field strength
of the drive coil(s) increases, and the rotor speed
increases to the correct value.
8.4 TEMPERATURE COMPENSATION
The section which corrects the speed of rotation
of the motor as the ambient temperature changes
comprises varistors (Do, Dr, Du, Dr, Ds ) to
achieve temperature compensation.
o Do compensates Qtr. If Do were not provided,
an increase in temperature would cause an
increase in Q,1 collector current, and a corre-
spo n d in g in c r e a se in Q ' u , Q ,r, Q,o , Q rr, wi th
a rise in the base potential of Qo I Q6, and Qs2,
and an increase in the speed of the motor.
o Ds, D. provide the temperature compensation
for rotor magnetism. It'lagnetic field strength
drops at -0.18Vo1"C with an increase in tempera-
ture. For this reason, if Ds , Du are not provided,
even at the proper rate of rotation, the voltage
generated in the drive coils would drop, because
the comparator would indicate that the speed
has dropped, and so the molor speed would.
D. (33-1/3) D6 (45 rpm) raise the potential at
the base of
Q,r
as the temperature rises,
preserving the balance of Q'u and Qrr, and
maintaining proper speed.
. Da and De compensate Dr and Qts
f
(RD-9.18) is a zener diode. The zener temper
ture coefficient is O.OGVofC. If D, and Dg a
not provided, as the temperature rises the zen
potential will rise, so that the Vg-s of Qte drop
dropping the emitter potentid (the standa
voltage) of Q,r. If the standard voltage rix
the speed of the motor also rises. This is tl
reason for the compensation by Ds and De f(
the rise in Dr zener potential and the drop
Vs-e potential of Qrr. The temperature coefl
cient of De (VD1222) is -3.6mV/'C.