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8-3
CIRCUIT DESCRIPTION
CPU PWB PWC-4651 Check Points
The check points are specified below, to be needed in the case of abnormal operation when the CPU PWB is put
in service.
For the operation of the CPU PWB, two types of jigs are available; the JTAG jig and the function jig (simplified
version).
The check points specified below are applicable when the function jig is used and any malfunction occurs.
Circuit Operation of the CPU PWB PWC-4651
1. Power supply system
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1 Power supply to the CPU PWB
The power supply to the CPU PWB is controlled by the POCP.
Pins 1 and 2: +5V for standby ...................... D7603 (LED) is lit.
Pin 6 : +5V for main ........................... D7602 (LED) is lit.
The fuses (F7601, F7602) are mounted behind the respective pins of the connector. If the connector pins are
applied with a voltage but the above-mentioned LEDs are not lit, the related fuses may have blown out. Turn
off the power supply toward the CPU PWB and measure the resistance value between both ends of the
above-mentioned fuse by means of a circuit tester. If this section is found short-circuited, the fuse is normal.
If the measured value is found infinity, this fuse is then broken.
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2 Standby power supply system
The standby power supply provides +5V and +3.3V.
Voltage +5V is fed from Pins 1 and 2 of the above-mentioned POCP. This voltage is used to drive the circuits
of peripheral boards that work at +5V and also used as the power supply for the I2C bus and buffer circuit to
be connected.
Voltage +3.3V is produced from +5V by the regulator of IC7604. Most circuits in the CPU PWB are driven at
this standby voltage of +3.3V.
Some devices are driven by another power supply obtained from +3.3V by the aid of the regulator IC.
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3 Main power supply system
The main power supply also provides +5V and +3.3V.
This power supply is used for the interface circuits of the PWB that works on the main power supply system
when installed in the projector.
Voltage +5V is fed from Pin 6 of the POCP connector.
Voltage +3.3V is produced from +5V by the regulator of IC7604 and IC7606.
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