Each rotation of the wheel produces a corresponding output pulse from the optical
interrupter IC in the Color Wheel assembly. This 180 Hz output signal is returned to the
L board at L2/pin 3.
Drive Waveforms
The following motor drive waveforms were taken with no video input (unused video 3
selected). Cold ground was used instead of the motor common (L3/pin 1), because it
was easier to access and since we only need to determine the presence of the 3 motor
drive signals. If the neutral / common (L3/pin 1) is used as the scope ground, the entire
sine wave will display instead of missing the top 1/3
rd
of the sine wave shown in
channels 1 & 2.
Color Wheel Motor Drive Signal into DLP connector L3
Waveform Description
Voltage
Frequency
Location
Channel 1 Phase 1
5Vp-p + 8V
spikes
738 Hz
L3/pin 4
Channel 2 Phase 2
5Vp-p + 8V
spikes
738 Hz
L3/pin 2
Channel 3 Neutral /
common.
2Vp-p + 5V
spikes
2.127 kHz
L3/pin 1
Time base = 0.5ms/div.
Phase 1
Phase 2
Neutral / common
Figure 13 - Color Wheel Motor Drive Waveforms
Color Wheel Assembly Outputs
The color wheel assembly contains two circuits and therefore has two outputs.
Color Wheel Output - Refer to figure 14. Once the CW motor turns, its shaft rotation is
monitored by an optical sensor (photo interrupter). The optical sensor outputs 180 Hz
pulses at L2/pin 3 (speed of the motor). This signal serves three purposes:
1. Informs the microprocessor on the DG board that the color wheel is rotating. The
absence of this signal causes the microprocessor to shut the TV off (see
protection circuit part of this book).
19
