Tv Start-Up, Tv Normal Run And Stand By Mode Operations - NEC DTE-29U1TH Service Manual

5-9 TV start-up, TV normal run and stand-by mode operations
5-9-1 TV start-up operations
* Schematic diagram for start-up operations
D801... D804
(GRAETZ BRIDGE)
SW801
POWER SWITCH
MAIN AC VOLTAGE
* TV start-up and microcontroller initialization
- When SW801 power switch is pushed, main AC voltage is applied to T801 transformer (after
rectification by D801...D804 diodes). Then, T801 SMPS transformer starts operating and
supplies DC voltage to I823 (3.3V regulator).
- This regulator provides 3.3V DC voltage to I501 microcontroller power supply pins (pins 54,
56, 61) and to the reset pulse circuit which provides reset pulse to I501 microcontroller reset
pin (pin 60).
- Then, the microcontroller starts its initialization. Its power pin (pin 63) is set to high which
allows delivery of power supply voltages (123V, 8V, 5V...). At this step, all IC s start working
but no picture appears on screen: I501 IC doesn t provide horizontal drive voltage.
- Then, the microcontroller consults I702 EEPROM via I2C bus to know the last TV set mode
(normal run mode or stand-by mode ) before switching off.
I823 REG 3.3V
IN G N D
1 2
12
8V
T801 SMPS TRANSFORMER
2 4
L801
3
D
I801 MOSFET AND
CONTROL IC
Start-up operations
-43-
O U T
3
L511
L510
61 56
Vddp Vddc VddA
I501
MICROCONTROLLER PART
SDA
SCL
2
6
I702
E E P R O M
Service Manual CP-785F
RESET
IN
PULSE
CIRCUIT
O U T
L512
60 63
54
Reset N Power
3
5