Panasonic Z8 User Manual

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Technical Guide

Colour Television

Z8 Chassis

Circuit Explanations

Panasonic

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CONTENTS

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Block Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4. TV Signal, Control and Teletext Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5. Horizontal Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6. Vertical Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7. East-West Correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8. Memory (EEPROM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

9. Colour Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

10. MSP3415D Audio Signal Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

11. AF Output Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

12. Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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1.Introduction

We at Panasonic realise that the service engineer needs to understand the circuitry inside the TV and for this need, we have produced this Technical Guide.

This Technical Guide contains information for Z8 chassis and should be used in conjunction with the relevant Service Manuals for this chassis.

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2.Block Diagrams

2.1. Control Block Diagram

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2.2. Power Supply and Deflection Block

Diagram
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2.3. Video and Mono Audio

Block Diagram

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2.4. Video and Stereo Audio

Block Diagram

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3.Power Supply

The mains AC voltage used for Z8 is fed via connector E2 situated on the E-Board. From the connector E2 the mains AC power supply is fed via the main TV On/Off switch S801 and line suppression filter L801 before being fed to the standby transformer T801.

At the standby transformer T801 the AC supply splits into two paths.

The first path sees the AC supply being fed to the normally open contact of the standby relay RL801.

The second path has the AC supply being fed via the windings P2/P1 of the standby transformer T801.

3.1. Standby Power Supply Circuit

The standby transformer T801 has the AC supply as just mentioned being fed via the primary winding P2/P1.

The output of the secondary windings S2/S1 of the standby transformer is fed to the bridge rectifier D1201, where the AC voltage is full rectified. Here the supply takes two paths.

The first path provides smoothing to the supply via capacitor C1201 before being fed to IC1202 pin 1.

The output at pin 3 is smoothed further by capacitor C1203, and the 5V standby supply output is fed to the EEPROM IC1103, the remote control receiver IC1104 and the Q-Link circuit. The 5V standby supply is also fed to IC1201, where the output at pin 3 is smoothed via C1204, to provide 3.3V standby supply to the Ultimate One Chip (UOC) IC IC601 pin 61, and the reset IC IC1102. This 3.3V is also used to bias the standby relay control transistor Q1204.

The second path from the bridge rectifier sees the supply voltage being fed via resistor R1202 to the standby relay RL801 and the relay winding to the collector of transistor Q1201. Transistor Q1201, which is controlled by Q1204, is responsible for switching the TV in and out of standby, under the control of the UOC IC IC601 pin 1.

The two supplies mentioned allow the circuits to operate during standby, which is required to process the switch ON command from the remote control or local keys, allowing the TV to be switched out of standby.

To reduce the load on the standby transformer T801, a 10V supply is fed from transformer T552 pin 6 via rectifying diode D554, R1209 and D1205, to pin 1 of IC1202.

3.2. Power Supply Circuit

The STR-F6523, IC801 is used in the Z8 power supply to control and regulate the power supply operation. This device features over-voltage protection and thermal shutdown. The output stage of the IC incorporates a built-in MOSFET switching transistor.

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3.3. Operation

The supply voltage for the main power supply circuit is fed via the standby relay RL801 to the bridge rectifier D802 where the AC voltage is fully rectified and smoothed by capacitor C809.

This smoothed DC voltage of approximately 300V then feeds the supply to pin 3 of the switched mode power supply IC IC801, where the DC voltage is held at the drain of the internal MOSFET, by its parallel zener diode.

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3.4. Start Up

A start-up circuit is used to start and stop the operations of the control IC IC801 (STR-F6523), by detecting the voltage appearing at the VIN terminal, pin 4.

At start-up, capacitor C810 is charged via R804, which causes the voltage at pin 4 of IC801 to increase. Once VIN terminal pin 4 voltage reaches approximately 16V, IC801 begins to operate and drive the internal power MOSFET, causing current to flow through the drain/source terminals at pins 3 and 2, and to the winding B1-B2 of switching transformer

T802 via L803 and R809. The current at terminal B1 is split into two paths.

The first path follows the current being fed to the winding B1-B2 and back to pin 4 of IC801 via R811 and D805. Once the control circuit starts operation, the voltage at the VIN terminal pin 4 of IC801 starts to decrease. However, the drive winding voltage reaches the set value before pin 4 voltage drops to the shutdown voltage of 10V. Hence the voltage supply to pin 4 is maintained.

The second path is connected from terminal B1 to P2 of the FBT. This causes current to flow via the winding P2-P1, which provides the +B supply to the FBT T552 pin 9.

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3.5. Oscillator and Constant Voltage

Control Circuit

The oscillator within IC801 makes use of the charging and discharging of internal capacitor C1 (4700pF) and generates pulse signals which turn the internal power MOSFET On and Off. The constant voltage control of a switch mode power supply is performed by fixing the OFF time of the MOSFET (around 50uS) and changing the ON time in the pulse width control operation.

3.5.1. ’ON’ Condition and Time

When the switching power MOSFET is ON, C1 begins to charge.

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3.5.2. From ’ON’ to ’OFF’

When the voltage on C1 reaches (approx.) 6.5V, the output from the oscillator is reversed, and the internal switching power MOSFET switches OFF.

3.5.3. ’OFF’ Condition and Time

With the power MOSFET now OFF, Capacitor C1 starts discharging through R1, at the fixed time determined by the time constant C1, R1.

3.5.4. From ’OFF’ to ’ON’

When C1 voltage has dropped to around 3.7V, the output from the oscillator is reversed again and the power MOSFET again turns ON, thus repeating the cycle.

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3.6. Regulation

The power supply ON time is changed by controlling the the charge current of the internal capacitor C1. D804 is a photocoupler, which provides the drive current to the ’FB’ (Feedback) terminal of IC801 pin 1 via D812 and R806. The photocoupler current varies in response to the output from pin 2 of comparator IC IC802.

IC802 pin 1 monitors the +B supply voltage via the zener diode D814 by comparing it with a reference voltage established internally within IC802.

If the AC mains input voltage to the switched mode power supply increases, the +B voltage level tends to rise. This results in an increased current flow to the FB terminal, pin 1 of IC801 via the photocoupler D804, diode D812 and resistor R806. Increasing the rate at which C1 charges, causes the power MOSFET ON time to reduce. This in turn causes the +B level to return to its nominal value.

3.7. Drive Circuit

The drive circuit charges and discharges the capacitance between the gate and the source terminals of the internal power MOSFET, by receiving pulses from the oscillator. The basic circuit configuration is a totem-pole type connection of transistors. Since the maximum sink current (0.3A) can become active even when the VIN voltage is lower than the shutdown voltage, the drive circuit turns off the MOSFET without fail.

3.8. Protection Circuitry

3.8.1. Over-voltage Protection (OVP)

Over-voltage Protection is used to protect IC801 if VIN pin 4 terminal rises to approximately 22V. Although it basically functions as protection for pin 4 against overvoltage, it is also used to protect against overvoltage of the secondary output (in the event of failure of the regulation, for example). This is because pin 4 is supplied by winding B1-B2 of transformer T802, this voltage being proportional to the output voltage of the secondary side.

3.8.2. Over-current Protection (OCP)

Overcurrent Protection is performed pulse-by-pulse by directly detecting the drain current of the internal power MOSFET. Since the detection voltage is monitored by an internal comparator of IC801, constant temperature stabilisation is also achieved.

The Drain-Source current through the power switching MOSFET is passed via the resistor R809, which develops a voltage across it. The input voltage to IC801 pin 1 (OCP/FB) is passed to an internal comparator. When this input voltage exceeds a pre-determined value, the drive output is pulled LOW, resulting in the power MOSFET switching OFF.

3.8.3. Latch

The latch circuit is used to pull the output of the oscillator LOW (switching MOSFET OFF) when the over-voltage protection or thermal shutdown circuits are activated.

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10V

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In this condition the VIN terminal pin 4 decreases until the shutdown voltage of 10V is reached. At this point pin 4 begins to rise again but when it reaches the start up level of 16V, the latch circuit continues to stop the drive.

When the latch is on, VIN voltage at pin 4 increases and decreases within the range 10V to 16V, as shown in the above diagram, and is prevented from rising normally.

Cancellation of the latch circuit operation is achieved by restarting the AC input to the circuit after switching off the TV.

3.8.4. Thermal Shutdown

This circuit triggers the latch when the body temperature of the IC exceeds 140EC. The temperature is sensed by the control IC, but also works against overheating of the MOSFET, as both are mounted on the same lead frame.

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3.9. Secondary Supplies

On the secondary side, the transformer T802 supplies the following voltages:

:+12V to supply the horizontal driver stage.

:+20V to supply the East/West correction IC IC701.

:+27V to supply the audio output IC IC251.

3.9.1. +12V Supply

The signal from pin 16 of T802 is rectified by diode D851 and smoothed by capacitor C856. The 12V supply voltage is then applied to the horizontal driver transformer T553 via diode D501 and resistor R503. During start-up, the 12V supply feeds the horizontal stage as mentioned. However, when the whole power supply is up and running normally, the supply voltage from the secondary of T802 is no longer required. The horizontal stage now takes its 12V supply from the FBT T552. This is required to reduce the load on the secondary and provide drive current to the horizontal driver transformer T553.

3.9.2. +20V Supply

The signal from pin 14 of T802 is rectified by diode D853 and applied to the series regulator IC702 to supply +20V to the East/West circuit (model dependant).

3.9.3. +27V Supply

The signal from pin 14 of T802 is rectified by diode D853 and applied to the emitter terminals of transistors Q851 and via resistor R855 to Q852. This voltage to Q852 is fed via the emitter/collector junction. At the same time, the signal from pin 13 of T802 is rectified by diode D852 to provide a voltage of +27V, which is fed to the audio output IC IC251.

This supply voltage of +27V however is too large for the above mentioned ICs when under load and so the supply voltage has to be reduced. As the load on the above ICs increases, the voltage drop across R856 increases causing the base of Q851 to become more negative with respect to its emitter. With Q851 conducting the base bias of Q852 becomes more positive with respect to its emitter, thus causing the supply voltage to the ICs to be reduced.

However by reducing the supply voltage to IC251, the

output power is also reduced. This is compensated for by the increased current flow via R853 / R854. This in turn ensures that the output power of the ICs is not affected.

3.10. Voltage Supplies

3.10.1. +12V Supply

The +12V supply is output from transformer T552 pin 4 and is rectified by diode D553. This rectified voltage is smoothed by capacitor C566 before being fed to the vertical output IC IC451 pin 6. The +12V supply also feeds the horizontal driver transformer T553 via diode D510 and resistor R503.

3.10.2. -12V Supply

The -12V supply is output from transformer T552 pin 5 and is rectified by diode D559. This negative voltage is smoothed by capacitor C564 before being fed to the ground terminal pin 1 of the vertical output IC IC451.

3.10.3. +10V Supply

A supply of approximately 10V is output from transformer T552 pin 6, and fed to diode D554. This rectified voltage signal is then smoothed by capacitor C554 before being fed to the series regulator IC852 and the standby voltage regulator IC1202.

3.10.4. +8V Supply

The 8V supply is derived from the 10V supply line which is fed to the series regulator IC852 pin 1. The output of IC852 pin 3, smoothed by capacitor C857, is used to supply 8V to the TV control processor IC IC601, RGB output stage (Y-Board) via connectors E8 and Y2 pin 6, sound processor IC2001 and SECAM IF audio switching IC IC201 (French models only). IC852 also supplies the 5V series regulator IC IC851.

3.10.5. +5V Supply

The 5V supply is derived from the 8V supply line which is fed to IC851 pin 1. The output at pin 3, smoothed by capacitor C851, is used to supply 5V to the tuner, reset IC IC1105 and the sound processor IC2001 (model dependant).

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4.TV Signal, Control and Teletext Processing

The TDA9350/60/80 series IC601 used on Z8 chassis, is a one chip solution in TV processing. The Philips Ultimate One Chip (UOC) IC combines the functions of a TV signal processor and teletext decoder as well as an embedded microcontroller

used to perform control processing. The TV signal and teletext processing stages will be looked at later. First, the control processing stage of the UOC IC will be examined.