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4.3 MOTOR
RUNAWAY
Check
power
supply
voltage
and
wiring connections.
Does the voltage between pins 6 and 7 of
PA3006 register about 3.4V ?
Defective
reference
bias circuit consist-
ing of R, ~ R,, VR,,
VR,,D,,
andD,,
or
defective
PA3006.
(Refer
to
the
"Motor Fails to Rotate"' section).
Hold the turntable platter still by hand,
and measure
the voltage at pin no.4 of
PA3006. Does the voltage register 2.9V,
and
then
3.4V
when
the platter is re-
leased at 33 rpm ? In other words, does
the
voltage
increase
as the rotational
speed increases ?
Defective PA3006.
4.4 ROTATIONAL SPEED ADJUSTMENT
Defective speed detector circuit consist-
ing of Rg ~ R,,, C,, C3, and D; ~ D,.
. Turn
the power
on, and adjust VR, and VR,
in turn to obtain accurate rotational speeds at
45 rpm and 33-1/3 rpm respectively (i.e. when
stroboscope appears to be stationary).
Screw driver ae
VRi (33 45 rpm)
VR2 (45 rpm)
Fig. 1
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