Hitachi DV-P505E, Service Manual

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12 Chapter 1
FRONT (FSW) SUBSTRATE CIRCUIT
1. FL MICOM (IC1701)
It performs communications with IC 1201 ( pins 5, 6, 8, 9 ), including the main frame key, FL tube
(IC1702) drive. In addition, it works also in standby mode.
2. INCLUSION OF MAIN FRAME KEY
Input is done to FL MICOM at pins 10~13 for operation of S1701 ~ S1709 of mainframe key. Remote
control signal is received by ultra-red receiver element (IC1703), output at pin 1 and input to IC 1201 at
pin 166.
3. FL TUBE DRIVE
Grid voltage of FL TUBE at pins 33~38 is controlled from FL MICOM at pins 39~44; anode voltage of FL
TUBE at pins 5~23 from FL MICOM pins 15~32, 35.
Filament voltage (AC 3.5V) is supplied from power source to FL TUBE at pins 1, 2, 41, and 42.
4. POWER INDICATOR
Control signals are output from A/V processor pins 17 and 18 to lights 2-color LED (LED1761) green or
red. When power button is pushed 'ON', P. ON/OFF signal is output from A/V processor pin 17 and it
switchs ON all system powers and red LED is lighten by a 5V; When standby, only STABLE signal is
output to light green LED.
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
AC110~240V impressed at AC inlet. After that, when FETQ1 turns 'OFF', the energy is released to the
secondary side power supply. Two diverse circuits from secondary side includes SW (S5V, S 8V, S-8V,
S12V) that are put ‘ON’ by A/V processor control. Signal (P. ON / OFF) of PG1201 pin 1 and permanently
'ON' supplies (A5V, A4.5V, AC3.5V, A-24V).
Detection of secondary side voltage is by A5V. D15, and C18 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.
S5V output is from A5V output and by intermediary of output control circuit Q7.
S4.5V is output from S5V diode D12.
D13 and C16 compose secondary commutating circuit of S12 that is for DVD-ROM drive use.
D13 and C16 compose secondary commutating circuits of S8V that is output by 3-terminal regulator IC2.
For audio circuit 5V power supply, AUD S5V is produced from S8V in 5V regulator IC1504 (in
DEC substrate).
D19 and C27 compose secondary commutating circuit of S-8V.
A-20V is negative power supply to FL tube. D16 and C23 compose its secondary commutating circuit.
AC3.5V 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 Q5,
Q6 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 and S8V, 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
.
By pulling off plug from wall socket, eliminating short circuit, replace destroyed parts, and plug in again,
the normal state will be restored in its secondary commutate.