JVC L-A31

Tracking
Force Dial
Counterweight
6-(6) Motor RPM Adjustments
1.
When
adjusting
33-1/3
or
45
RPM,
first
set,
in.
either
5
way,
the
fine
RPM
adjustment
VT
(VR801)
to
around
half
the
maximum
resistance
(the
center
of the
rotating
angle).
ry
2. Connector an oscilloscope between TP-1 and GND on
the motor board as shown at right (Fig. 14)
3.
Adjustments
Oscilloscope
@ 33-1/3 PRM adjustment
Set
SPEED
SW
(SW4)
to
33-1/3
RPM.
then
adjust
the
'
coarse adjustment VR (VR1) on the moior board so that =
the waveform on the oscilloscope has T = 20 msce.
@ 45 RPM adjustment . :
Set SPEED SW (SW4) to 45 RPM, then adjust the coarse vas!
adjustment VR (VR2) on the motor board so that the
waveform on the oscilloscope has T = 14.8 msec.
4. Finally, using the stroboscopic pattern (33-1/3 RPM) “TP4
and the accessory stroboscopic pattern for 45 RPM, con-
firm whether the respective adjustrnents are performed
properly.
7.
Block
Diagrams
Waveform
Shaper
50Hz
+20
(at
33-1/3rpm)
ne
67.5H2z
Power
|
{at
45rpm)
Supply
33-1/3pm
Power
Circuit
:
Switch
45
‘
al?
Pitch
,
rom
17
x
ontro
33-1/2rpm
j
Pa
ae
1
o—45r0m
/
'
Sc
'
m8
i
Speed
Select
Switch
/
i
:
|
i_..-
i
Soe
J
Fig.
15
Oe
ae
L-A3}
ee
-.
No.
2555