Power Supply Repair Guide - How to - Panasonic TC-32LX70, TC-32LX700 & TC-32LX85 LCD TV Power Supply Circuits Description & Troubleshooti

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Panasonic TC-32LX70, TC-32LX700 & TC-32LX85 LCD TV Power Supply Circuits Description & Troubleshooti

Thursday, 07 January 2010
This article is for the Panasonic 32 inch lcd tv model TC-32LX70/700 series power supply circuit descriptions. P Board (Main Power Board) When AC is applied to the TV, the Standby circuit of the P board outputs 5Vdc to the AP board. The STB5V passes through the AP board and enters the A board. On the A board The STB5V is converted to 3.3V to power the system control circuit for standby operation. The STB3.3V is also applied to the Remote Control receiver and the power LED on the V board. The MPU (IC1100) of the A board outputs the SUB_ON command to provide a ground connection to relay RL802 of the power supply board. On the AP board, the SUB_ON command is used to turn on a circuit (not shown in the diagram) that provides STB5V to relay RL802 via pin 15 of connector AP2/P2. When the relay is closed, DC voltage from the rectifier, approximately 105Vdc, is supplied to the LCD panel for conversion into 24Vdc. The output of the 24V generator passes through the P board and enters the AP board for conversion into SUB_5V, DTV9V (SUB_9V), and HQ3.3V. If the power button (main unit or remote control) is not pressed within 25 seconds after applying AC to the unit, the SUB_ON command goes low to disengage the power relay. When the power button is pressed, the SUB_ON command goes high to repeat the same operation. The voltages remain present until the unit is turned off. When the unit is turned on, the LCD panel’s inverter circuit uses the 24Vdc source to generate the 120Vac to illuminate the CCFLTs. The INV_ON command and the 12Vdc source enter the panel’s drive circuit via the connector AP2/P2 and P5 of the P board. The inverter circuit is monitored for abnormality. When a defect is detected, a SOS (High) output is provided to the A board MPU (IC1100) via Connectors P5 and P2/AP2. Main MPU (Power On Commands) - A Board The STB 5V output of the P board passes through the AP board and enters the A board when the unit is plugged into the AC outlet. IC5702 of the A board converts the STB 5V to 3.3V to power the system control circuit. Activation of the power switch causes transistor Q5712 to turn off and output STB 3.3V to pin 18 of the MPU. Upon receiving the STB 3.3V, the MPU (IC1100) outputs the TV-SUB-ON command via pin 8 of connector A4/AP4. The TV- SUB_ON command is routed to the P board to provide a ground connection for relay RL802 of the power supply board. On the AP board, The TV_SUB_ON command is used to turn on a circuit (not shown in the diagram) on the A board that provides STB_5V to relay RL802. As a result , the switch of relay RL802 on the P board closes to allow the output of 105Vdc to the LCD panel. The TV_Main_ON signal issued by IC1100 appears on pin 6 of connector AP4/A4 to enable the output of the sound+12V DC/DC converter. Pin 105 of IC1100 outputs the PANEL VCC command to the AP board to turn on the 12V DC/DC converter. The 12V output is provided to the panel via the P board. Caution: Measure the 105Vdc source between pin 1 and 3 of connector P3. Hot ground must be used. Standby Operation - AP Board When the main power switch is activated, it is sensed on the A board by the MPU IC1100. The TV_SUB_ON signal is subsequently issued in response on pin 8 of connector A4/AP4. It turns on the transistors Q7224 and Q7223 to output the “Relay voltage on pin 15 of connector AP2/P2. The TV Sub_On signal is also provided to the relay via the resistor R7208 and pin 17 of connector AP2/P2. This pulls the contacts of the AC relay on the P board. The AC input is rectified and provided to the LCD panel for conversion into 24Vdc. The 24V is then provided to the inverter circuit of the LCD panel to produce the 120Vac that powers the backlight CCFLTs. The same 24V passes through the P board and enters the AP board for conversion into other voltages. The over-voltage protection circuitry affiliated with each of the regulators located on the AP board monitors for over-voltage conditions. It is designed to turn off the AC power by disabling the SUB_ON command that turns on the AC relay. When an over-voltage condition is detected on the AP board, the voltage at the base of transistor Q7207 goes “high” to turn on Q7207, Q7206, Q7205, and Q7204. The TV_SUB_ON voltage at pin 17 of connector A2/AP2 is now grounded through Q7204 and the unit shuts down. To turn the unit back on, disconnect and reconnect the AC cord before pressing the power button. SUB Voltages and Over-voltage Protection The AP Board is responsible for the regulation, distribution and dissemination of all secondary voltages derived from the 24V output of the P Board. During standby operation, the 24V output of the P board biases the transistor Q7208 into operation, causing its collector to become “low”. The low at the collector of Q7208 causes the transistors Q7226, Q7227, and Q7450 to turn off. As a result, IC7205, IC7209, and IC7233 go into operation to immediately provide the Sub_5V, DT9V, BT30V, and HQ 3.3V output. The over-voltage protection circuitry affiliated with each of the regulators monitors for excessive current and over- voltage conditions. It is designed to turn off the AC power by disabling the SUB_ON signal needed to turn on the AC relay. Main Voltages and Over-voltage Protection When the unit is turned on, the TV_Main_On command (high) of IC1100 biases the transistor Q7212 into operation, causing its collector to go “low”. The low at the collector of Q7212 causes the transistor Q7225 to turn off. As a result, IC7215 goes into operation to provide the Sound_15V output. When the Panel_VCC_On command is issued, transistor Q7702 turns on causing Q7701 to turn off. Consequently, IC7212 turns on and outputs 12V. This voltage enters the A board via the connector AP4/A4. It is also provided to the LCD panel via the connector AP2/A2, the P board, and the connector P5 (not shown in the diagram). The over-voltage protection circuitry affiliated with each of the regulators monitors for excessive current and over-voltage conditions. It is designed to turn off the AC power by disabling the SUB_ON signal needed to turn on the AC relay. Inverter_On Command and Protection The INV_ON/OFF command (high) of the MPU, IC1100 of the A board, passes through the AP and P boards before entering the LCD panel. On the LCD panel, it triggers the operation of the inverter to produce the 120V AC that powers the backlight CCFLTs. To avoid catastrophic failures, when the Panel_VCC_ON pin of the MPU goes “low”, Q7805 turns off. Consequently, Q7806 turns on to disable the operation of the inverter. Over-Current Protection Circuit The protection shutdown circuit is designed to monitor for a short or loss of the SUB_9V, SOUND_VCC, BT30V, and the Panel VCC sources. If any of these voltage sources goes low, Q7210 turns on. As a result, the collector of Q7210 goes high to signal a shutdown condition to IC1100 on the A board. The TV_SUB_ON pin of IC4002 goes low to de- activate the AC relay on the P board. During standby operation, the 24 volt output of the P board biases the transistor Q7208 into conduction, causing its collector to become “low”. The low at the collector of Q7208 causes the transistors Q7450 to turn off. As a result, IC7233 goes into conduction to immediately provide the HQ 3.3V output. When the 24 drops below the reverse breakdown voltage of D7206, transistor Q7208 turns off and transistor Q7450 turns on. IC7233 ceases to operate causing Q7451 to turn off and Q7452 to turn on. Consequently, the SUV_9V line is now grounded. Diode D7220 becomes forward biased and Q7210 outputs a high to trigger the shutdown of the unit. Over-Current Protection Circuit 2 Sound_VCC Protection During normal operation, the 24 volt output of the P board biases the transistor Q7208 into conduction, causing its collector to become low. The low at the collector of Q7208 causes the transistor Q7214 to turn off. When the PANEL_MAIN_ON command (high) is issued Q7212 turns on. Consequently Q7225 turns off, and IC7215 goes into conduction to provide the SOUND_15V output. When the 24 drops below the reverse breakdown voltage of D7206, Q7208 turns off, Q7214 turns on to ground the PANEL_MAIN_ON voltage. Q7212 turns off and Q7225 turns on. IC7215 ceases to operate and the Sound_VCC is no longer output. During normal operation, the anode of D7469 receives 5V and the junction of D7469, D7470, R7486, and R7492 receives 12V. Due to this condition, the transistor Q7210 remains off. If the SOUND_15V line becomes shorted, diode D7469 goes into conduction to turn Q7210 on. Consequently Q7210 outputs a high to shut down the unit. Panel_VCC Protection During normal operation, the 24 volt output of the P board biases the transistor Q7208 into conduction, causing its collector to become low. The low at the collector of Q7208 causes the transistor Q7508 to turn off. When the PANEL_VCC_ON command (high) is issued, Q7702 turns on. Consequently Q7701 turns off, and IC7212 goes into conduction to provide the PANEL_12V output. When the 24 drops below the reverse breakdown voltage of D7206, Q7208 turns off, Q7508 turns on to ground the PANEL_VCC_ON voltage. Q7702 turns off, and Q7701 turns on. IC7212 ceases to operate and the Panel_VCC is no longer output. During normal operation, the anode of D7472 receives 5V and the junction of D7472, D7473, R7493, and R7488 receives 12V. Due to this condition, the transistor Q7210 remains off. If the Panel_12V line becomes shorted, diode D7472 goes into conduction to turn Q7210 on. Consequently Q7210 outputs a high to shut down the unit. When the unit is turned on, the TV_Main_On command (high) of IC1100 biases the transistor Q7212 into operation, causing its collector to become “low”. The low at the collector of Q7212 causes the transistors Q7225 to turn off. As a result, IC7215 goes into operation to provide the Sound_15V output. Click here for more lcd tv repair information.
Last Updated ( Thursday, 07 January 2010 )