Power Circuit - NEC AccuSync LCD51VM Series Service Manual

1. Power Circuit

1.1 Power Input
5V DC is input (S403) from power Board to interface Board.
1.2 DC to DC Circuit
U403 generates 3.3V for scaling IC, panel and other ICs. U404 generates 2.5V for scaling IC.
Audio IC, Flash Memory use 5V directly.
1.3 Panel Vcc Control
Q405 and U409 are used for panel power control. The control signal is from scaling IC U405 (pin 40:
PPWR).
While the PPWR stay at High level; the panel voltage is 5.0V.
While the PPWR stay at Low level: the panel voltage is 0V.
2. Scaling IC
Scaling IC U405 has micro controller, ADC, scaling, color control and LVDS transmit functions.
2.1 Clock Circuit
Crystal X401 generates 14.318MHz clock signal for Scaling IC.
2.2 I2C Buses
There are 2 sets of I2C bus in the circuit:
One I2C is used for DDC. EDID data is stored in U401, and this I2C bus is connected to U405 (pin 8:
SDA, pin 9: SCA) for DDC/CI.
The other I2C is used for OSD parameter storing. It connects U405 (pin 36: SDA, pin 37: SCA) and U408.
2.3 Key Scanning
Following ports are used fro key scanning.
U405 pin13: "POWER" key
U405 pin34: "Auto/Reset" key
U405 pin29: "SELECT" key
U405 pin33: "+" key
U405 pin32: "-" key
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