Ricoh FT7770 Service Manual page 75

- Main Board Input to Scanner Motor control Board -
The main board CPU controls the scanner motor speed and is responsible for
maintaining proper scanner speed and direction. The following is a descrip-
tion of the signal lines that the main board CPU controls.
PLL (Phase Lock Loop):
The main board applies a reference clock
motor control board.
from the scanner motor.
match, the PLL will either increase or decrease the scanner speed until the
pulses from the reference clock and encoder are equal.
REF CLK:
The reference clock (REF CLK) is a pulse applied to the scanner motor con-
trol board. This is a reference signal so the actual scanner speed (encoder
pulse) can be compared.
tions.
PHASE:
The phase control will correct for LAG if the encoder signal and reference
signal from the main board do not match.
GAIN:
Here, the output changes the amplification ratio on return scan, speed down,
This ratio change is needed in order to apply more current to
and brake.
the scanner motor. During the return scan, the scanner speed increases and
more torque is needed.
REVERSE:
The reverse signal is applied to change the voltage applied to the scanner
motor. A negative voltage is applied during forward scan and a positive
voltage is applied during reverse scan.
FBIAS:
The main CPU changes the bias voltage applied to the scanner motor control
board. During forward scan +4 volts is applied, whereas during return scan
-6 volts is applied.
SCANNER ON:
Here, the CPU controls the ON timing of the scanner motor.
This reference clock should match the encoder pulse
If the pulse length from the encoder does not
The two pulses should be equal under ideal condi-
2-19
pulse (REF CLK) to the scanner
30 April, '89