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3.4
PHYSICAL DESCRIPTION OF THE SERVO
PCBA
The Servo PCBA is approximately 127 mm (5.0 inches) long by 38
mm
(1 .5 inches)
wide. Figure 3-15
illustrates
the placement of test points and connectors.
0
/J1
~[~tt:::}
SERVO
~
i i
JUMPER
[ +t-}
DRIVE
-L
O
::
MOTOR
SPINDLE
_ / - - - - - - - - - - ~ -
SPEED CONTROL
3.4.1
Input
Control Lines
Functional Description
Figure 3-15
Servo PCBA
When the logic board receives a true (low) Motor On signal, a true (low)
signal
is sent
to
the
servo board
(N
MO-
TOR ON) (see Figure 3-16). This signal turns on the
regulator
(01 ), and the motor's speed accelerates to
300
rpm (
±
1.5%).
R4
is
adjusted for a motor speed of 300 rpm.
The motor supplies a 12-volt AC tachometer signal to the servo board for regulation control.
Circuit Description
The Motor On signal comes in at Pin 7 of the servo board (see Section 3.3.1.2). This turns off
02,
allowing
the sig-
nal
to
be sent to the base of 01
.
The signal to the base of 01
is
the output of the regulator IC Pin 8.
This
is con-
trolled
by the tach input at Pin 1 and Pin 2 of the servo board. The tach signal is an AC signal
of
twelve (12) volts.
The other input to the regulator is from the voltage divider R3, R4, and RS. This voltage is
adjustable by R4, a
potentiometer, to produce the proper amount of current through 01 to the drive motor.
3-18
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