TH-42PHD5 -TH-50PHD5 - TH-42PHW5 -TH50PHW5 - DISASSEMBLE - POWER SUPPLY DESCRIPTION

If you are not familiar with electronics, do not attempt to repair.  Whether you suffer fatal electrical shock! Instead, contact any experienced service technician, or the nearest service center.

REAR COVER REMOVAL

• Remove the 27 screws, shown, and then pull away the rear cover.

• Remove the six screws, shown and then pull away the rear shield cover.

LOCATION OF LEAD WIRING

• High frequency electromagnetic signals can create electrical interference within the unit.
• Be sure to route all wires through their respective harnesses reference.

STANDBY POWER SUPPLY

• The standby power supply provides the necessary DC voltage for the system control Microprocessor, Reset circuit and the EEPROM. D421 rectifies the incoming AC Voltage and applies it to the transformer T402 and the standby B+ control circuit IC400. The output pulses of IC400 are then applied to the primary side of transformer T402. Diode D439 rectifies the AC output at pin 15 of the secondary of T402 to create STB (Standby) voltage for the system control circuit.
• The AC output at pin 14 of the secondary of T402 is rectified by diode D440 to create the DC voltage for the power relays. Transistor Q418 creates the ground path for power relay RL401.
• Transistor Q417 provides the ground path for the In Rush Current relay RL400. The Opto-coupler D431 provides feedback to the STB control circuit for voltage regulation.

STANDBY POWER - BLOCK DIAGRAM

MAIN POWER SUPPLY
Working principle

• The power factor control circuit operates like a boost regulator. The incoming AC voltage, after being switched on, enters the rectifier D402 where it is converted to DC. The Power Factor Control (PFC) circuit converts the DC level to 400Vdc.
• The negative side of the bridge rectifier D402 connects to ground via a resistor. As current flows through the resistor, the resulting voltage drop enters pin 5 of connector P19/P19A of the power factor control circuit board. The power factor control circuit board is a switching control oscillator circuit which boosts the input voltage at pin 2 of the transformer T401 to 400Vdc. As the pulses are output at pin 4 of connector P19/P19A, the transistors Q400~Q405 are switched On/Off controlling the charge and discharge time of the inductor L401. The output voltage is monitored via pin 11 of the connector P19/P19A. The resistor R548 adjusts the output voltage to 400Vdc. The 400Vdc output to pin 2 of the transformer T401 subsequently enters the drain of transistor Q416.
• VCC and Start-up voltage for the low voltage power supply is provided to IC650 of the P5 Board by the standby power supply circuit (not shown).
• Upon start-up of the switching control circuit, a pulse width modulated signal is output at pin 9 of connector P18/P18A to drive the switching transistor Q416. When Q416 is on, current flows via the primary winding of transformer T401 and Q416. As current flows through the transformer, energy is built up and stored in the transformer.
• When Q416 turns off, the energy within the transformer begins to collapse. As the field collapses, energy is released in the windings of the transformer to provide the secondary voltages.
• The rectified AC output at pin 10 of transformer T401 is applied to IC401 where it is regulated to 18V. This voltage is used to power the Drive Oscillator circuit board.
• The 13.5V source and the VDA source voltage levels are monitored by IC650 of the P5 Board. A voltage increase of the 13.5V or an increase in the current flow of the VDA source causes IC416 to conduct harder, allowing more current to flow through the LED inside opto-coupler D432. This increases the conduction of the transistor inside D432.
• Conversely, a decrease in the 13.5V supply voltage or a decrease in the current flow of the Vda source decreases the conduction of IC416. Any change in the conduction of IC416 is monitored by pin 10 of IC450.  As a result, the pulse width modulated output at pin 10 of IC650 adjusts to keep the output level of the power supply constant. R545 is used to adjust Vda to the proper voltage level.

Main power supply block diagram

HIGH-VOLTAGE POWER SUPPLY

• The P3-Board contains the drive voltage oscillator circuit that develops the Vsus voltage needed to drive the Scan and Sustain boards. Operation begins with the 18Vdc supply being applied to pin 12 of connector P15. This voltage serves as start up voltage for IC601. Q604, connected to pin 7 and 9 of the IC, provides Oscillation control. The oscillator generates a trapezoid pulse that is input to a PWM [Pulse Width Modulator] circuit (not shown) to control the output voltage. The PWM output at pin 2 of IC601 is applied to pin 2 and 3 of IC600. This IC is a wave driver that provides two square wave outputs at opposite polarity. The two signals are then output to the P1 board as H OUT at pin 1 and L OUT at pin 6 of connector P15.
• Amplification of the two signals is performed the transistors Q407, Q408, Q409, Q410 before being applied to the transformer T400. The output of the transformer is provided to the SC-Board via pin 1 and 2 of the connector P2 and to the SS board via Pins 2 and 3 of the connector P1.
• Voltage feedback is provided via pin 8 of connector P16. This voltage enters pin 5 of IC601 for voltage regulation. R625 is used to set the output at the desired level.

Note: The voltage level of the Vsus output is not mentioned because it is different for each plasma display panel. This voltage level can be found on the panel information label located on the heat sink of the panel.

• Over-voltage protection (OVP) is provided via pin 6 of connector P16. This voltage enters pin 4 of IC601 for immediate shutdown of the IC if the Vsus voltage rises to an undesired level. The OVP feedback is also provided to the system control circuit via pin 13 of connector P15 for immediate shutdown of the entire unit.
• The P7 (High Voltage Protector) and P8 (Low Voltage Protector) circuit boards monitor the DC output of all power supply boards. If any of the inputs is higher than the desired level, a DC level is output via the “SOS IN” line to pin 1 of connector P16. The operation is the same as the OVP input at pin 6 of the connector P16.

H/V BLOCK DIAGRAM

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