Front (Fsw) Substrate Circuit; Power Supply Circuit - Hitachi DV-P250U Manual De Servicio

FRONT (FSW) SUBSTRATE CIRCUIT

1. FL MICOM (IC1701)
It performs communications with SH MICOM ( pins 6, 7, 10 ~ 13, 15, 25 ), including the main frame key
and remote control operation, FL tube (IC1702) drive, and lighting of power indicator. In addition, it works
also in standby mode. When power is 'ON', it outputs control signal at pin 33 to start all power sources and
voltages and unlock short circuit toward GND of SH MICOM reset IC (IC1605) output.
2. INCLUSION OF MAIN FRAME KEY AND REMOTE CONTROL OPERATION
Input is done to FL MICOM at pins 2~4 for operation of S1701 ~ S1715 and S1761 ~ S1763 of mainframe
key. Input is done to FL MICOM at pins 23, 24, 37~40 for jog shuttle sw (S1718) operation. Remote
control signal is received by ultra-red receiver element (IC1703), output at pin 1 and input to FL MICOM at
pin 26.
3. FL TUBE DRIVE
Grid voltage of FL TUBE at pins 33~38 is controlled from FL MICOM at pins 41~46; anode voltage of FL
TUBE at pins 5~23 from FL MICOM pins 51~69. Among which FL MICOM pins 65~69 are connected to a
20V by R1743~R1747 because no pull down resistance is built-in in IC.
Filament voltage (AC4.2V) is supplied from power source to FL TUBE at pins 1, 2, 41, and 42.
4. POWER INDICATOR
Control signal output from FL MICOM pins 34 and 35 then puts LED driving transistors Q1703 and Q1704
'ON' or 'OFF' then lights 2-color LED (LED1761) green or red. When power is 'ON', Q1704 is 'ON' and the
green LED lights up; when standby, Q1703 is 'ON' and the red LED lights up.

POWER SUPPLY CIRCUIT

1. ESSENTIAL OF POWER SUPPLY CIRCUIT OPERATION
Power supply is RCC switching type. Energy is stored in transformer T1, when FETQ1 is 'ON', by AC100V
impressed at AC inlet. After that, when FETQ1 turns 'OFF', the energy is released to the secondary side
power supply. To diverse circuits from secondary side includes SW (S5V, S3.3V, S12V) that are put 'ON'
by FL MICOM control signal (P. ON/OFF) of PG1901 pin 1 and permanently 'ON' supplies (A5V, MUTE
A5V, AC4.2V, A-20V, A8V, A-8V).
Detection of secondary side voltage is by A5V. D8, C16, and C17 compose its secondary side
commutating circuit. It is fed back by photo-coupler PHC1 to primary side and maintains stable output
voltage and is supplied to FL MICOM and ultra-red reception element.
MUTE A5V is for AUDIO MUTE and supplied from A5V output.
S5V output is from A5V output and by intermediary of output control circuit Q3.
S3.3V is output from S5V at 3-terminal regulator IC2.
D11 and C24 compose secondary commutating circuit of S12 that is output by 3-terminal regulator IC3
and is for DVD-ROM drive use.
D11 and C24 compose secondary commutating circuits of A8V that is output by 3-terminal regulator IC4.
For audio circuit proper +5V power supply, AUD S5V is produced from A8V in 5V regulator IC1506 (in
DEC substrate).
D13 and C29 compose secondary commutating circuit of A-8V and it output -8V by transistor Q7 and
zener diode D20.
A-20V is negative power supply to FL tube. D14 and C33 compose its secondary commutating circuit and
output -20V by transistor Q6 and zener diode D17.
AC4.2V is for FL tube heater. To prevent fluctuation of output voltage due to that of power source, a self-
exciting push-pull circuit is used. It is input from A5V, passes DC/AC inverter composed of transistors Q8,
Q9 and transformer T2 and output. It supplies stable voltage without being disturbed by power source
fluctuations. It plays an important role in FL tube life maintenance and against brightness decrease.
2. OPERATION OF PROTECTION CIRCUIT
Protection circuits are different according to different power supplies.
For A5V and S5V,when load current increases and exceeds the control limit of the primary side of the
regulator, the over current protection circuit of the primary side operates and regulator output will
decrease suddenly. At the same time other outputs stop.
For S12V, S3.3V, and A8V, when load current increases and exceeds the control limit of 3-terminal
regulator, the internal over current protection circuit operates and output will suddenly decrease
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Chapter 1