NEC DLP CINEMA NC1600C, Service Manual

Page: 212 / 382

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8-7
CIRCUIT DESCRIPTION
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USB interface circuit
The USB interface circuit is of the A type and its connector is M7401. It is connected to the USB interface pin
of the CPU (IC7002) via the transformer T7401.
As a power supply for the connector M7401, +5.0V is fed through IC7402. The CPU controls IC7402 so that
the +5.0V power can be fed to and removed from the connector M7401. If a current of over 1A is carried
through the connector M7402 from the +5.0V power supply, IC7402 functions to suspend the supply of this
+5.0V power. (In this case, the current protection circuit is actuated.)
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Wired remote control circuit
Connector M7800 is a connecting connector for the wired remote control circuit. The power supply for the
remote control circuit is gained from Pin 2 of this connector at +4.0V. This voltage is obtained from Standby
+5.0V with the aid of the regulator IC7801. When the remote control circuit is connected with the connector
M7800 through a remote control cable of 16 meters long, the voltage is maintained at approximately 3.3V on
the remote control side.
Pin 3 of the connector M7800 is an input terminal for the remote control signals. The remote control signals
are gained at +5.0Vp-p on this PWB and processed for waveform shaping and level conversion at Q7806
and Q7808. When the signals are converted into +3.3Vp-p, they are entered in the remote control signal
decoder circuit of the ASSIST III (IC7200).
In the ASSIST III (IC7200), the entered remote control signals are decoded by hardware. Only when remote
control signals are identified as normal, the information about the entry of a remote control input is transmit-
ted from the ASSIST III (IC7200) to the CPU. If the input signals are identified as abnormal in the ASSIST III
(IC7200), the information about the decoded signals is not transmitted to the CPU.
Pin 1 of the connector M7800 is maintained at the GND potential.
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PC control interface M7700
Connector M7700 is an RS-232C port. It is used for communication with external devices. If it is connected
with a PC, a D-Sub 9-pin cable in straight connection is used.
Switch S7700 is a changeover switch used to select the destination of connection for the connector M7700.
This switch is of the Push & Lock type.
When the S7700 is pressed ON, the communication line of M7700 is connected to the RS-232C driver /
receiver of IC7702. It is then connected to the serial communication port (UART) of the CPU (IC7002).
If the S7700 is not pressed ON, the communication line of M7700 is connected to the connector POCT.
When it is incorporated in the projector, it is connected to D-Sub 9-pin of the mother board in the POCT
Sinama circuit.