Printronix p300 Maintenance Manual page 88

2–8. Power Supply
–continued
k. Motor Relay Trigger, P600 Only (Figure 2–43 and Figure 2–44)
The motor relay trigger is used to apply a high starting torque to the shuttle motor at rest and later discon-
nect the starting torque once the motor is running at the proper speed. When the printer is brought online, a
solid state relay is actuated to apply AC line voltage to the start winding. The start winding energy is added
to that of the run winding to produce a high starting torque. Once the shuttle motor approaches normal
operating speed, actuation of the relay ends and the start winding is de–energized.
The motor trigger relay circuit is shown in Figure 2–44. While the printer is offline, NSD is high, and the
clock counter and dual flip–flop are held in reset. When the printer goes online, NSD goes low releasing
the counter and flip–flops. The 2 MHz system clock, NCLK, is converted to 1 MHz (1 microsecond) by the
first element of the counter. The 1 microsecond pulse passes through a 17 stage divider and becomes a 59.7
millisecond pulse, which is further divided by stages of the clock counter to produce a 119.4 millisecond
pulse and a 238.8 millisecond pulse.
Then, 238.8 milliseconds after NSD goes low, the 238.8 millisecond pulse sets the upper flip–flop which
actuates the solid state relay and the motor begins turning. The MPU counter begins receiving MPU pulses
detected at the flywheel. A count of 96 is decoded at the output of the counter. Initially, the shuttle motor is
not turning fast enough for 96 MPU pulses to be generated before the 119.4 millisecond pulse resets the
MPU counter. The MPU counter is reset by the clock counter 59.7 milliseconds after the relay is actuated
and at 119.4 milliseconds later. The MPU counter is released midway between resets. Each time the
counter is released, it begins a new count. When the shuttle motor is turning fast enough, a count of 96 is
decoded and the lower flip–flop is set. The setting of the flip–flop halts the relay actuation and the start
winding is de–energized. The set flip–flop also resets and holds the clock counter and the MPU counter.
Counting stops until the printer is cycled offline/online again to keep the relay from being actuated at nor-
mal motor speed which would have a braking effect on the motor.
2–66 P300/P600 Principles of Operation