Panasonic Z8 User Manual
Technical Guide
Colour Television
Z8 Chassis
Circuit Explanations
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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.........................................................
1. Introduction
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We at Panasonic realise that the service engineer
needstounderstandthecircuitry insidetheTVandfor
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
2.4. Video and Stereo Audio
Block Diagram
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3. Power Supply
ThemainsACvoltageusedforZ8isfed viaconnector
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 viathe
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 theACvoltage is fullrectified. Herethe
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 5Vstandby supply output is fedto the
EEPROM IC1103, the remote control receiver
IC1104and theQ-Link circuit. The5V standby supply
is also fed to IC1201, where the output at pin 3 is
smoothed viaC1204, to provide3.3V standby supply
to theUltimateOne Chip(UOC) IC IC601 pin 61, and
thereset ICIC1102.This3.3V isalso usedto 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.
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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 thermalshutdown.The output stageof
the IC incorporates a built-in MOSFET switching
transistor.
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, wherethe 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 V
pin 4.
At start-up, capacitor C810 is charged via R804,
which causes the voltage at pin 4 of IC801 to
increase. Once V
terminal pin 4 voltage reaches
IN
approximately 16V,IC801beginstooperateanddrive
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
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terminal,
IN
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 V
terminal pin4 of IC801 starts to
IN
decrease. However, the drive winding voltage
reachestheset value before pin 4voltagedropsto the
shutdownvoltageof 10V.Hencethe voltage supplyto
pin 4 is maintained.
The secondpath is connected from terminal B1 toP2
ofthe FBT. Thiscausescurrent toflowvia thewinding
P2-P1,which providesthe+B supply totheFBT T552
pin 9.
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3.5. Oscillator and Constant Voltage
Control Circuit
Theoscillator withinIC801 makesuseof 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
byfixing theOFF timeof theMOSFET (around50uS)
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.
3.5.2. From ’ON’ to ’OFF’
When the voltage on C1 reaches (approx.) 6.5V, the
output fromthe oscillatoris reversed, and theinternal
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 voltagelevel tendsto
rise.This results in anincreased currentflowtotheFB
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 theinternalpowerMOSFET, 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)
canbecomeactiveevenwhentheV
than the shutdown voltage, the drive circuit turns off
the MOSFET without fail.
voltageislower
IN
3.8. Protection Circuitry
3.8.1. Over-voltage Protection (OVP)
Over-voltageProtectionisusedtoprotect IC801 if V
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
failureofthe 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.
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IN
16V
10V
t
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 developsa 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 driveoutputis 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.
In this condition the VINterminal pin4decreases until
the shutdown voltage of 10V is reached. At this point
pin4begins torise again but whenitreaches thestart
up level of 16V, the latch circuit continues to stop the
drive.
When the latch is on, V
anddecreases withinthe range 10Vto16V,asshown
in the above diagram, and is prevented from rising
normally.
Cancellation of the latch circuit operation is achieved
by restarting the AC input tothe circuit afterswitching
off the TV.
3.8.4. Thermal Shutdown
This circuit triggers the latch when the body
temperature of the IC exceeds 140
temperature is sensed by the control IC, but also
works against overheating of the MOSFET, as both
are mounted on the same lead frame.
voltage at pin 4 increases
IN
E
C. The
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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
stageas mentioned. However,whenthewholepower
supply is up and running normally,the supply voltage
fromthesecondary of T802isnolongerrequired. 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 thehorizontal
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
theabove mentionedICs whenunder load and sothe
supply voltage has to be reduced. As the load on the
above ICs increases, the voltage drop across R856
increases causingthe baseof 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.
Howeverby reducingthe supply voltagetoIC251, the
output power is also reduced. This is compensated
forbytheincreased current flowviaR853/ R854.This
in turn ensures that the output power of theICs is not
affected.
3.10. Voltage Supplies
3.10.1. +12V Supply
The +12V supply is output from transformer T552 pin
4andis rectified by diodeD553. This rectifiedvoltage
issmoothedbycapacitorC566before beingfedto the
vertical output IC IC451 pin 6. The +12V supply also
feedsthehorizontaldriver transformer T553 viadiode
D510 and resistor R503.
3.10.2. -12V Supply
The -12V supply is output from transformer T552 pin
5andisrectifiedbydiodeD559.This negativevoltage
issmoothedbycapacitorC564before beingfedto 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 voltagesignal isthen smoothed bycapacitor
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 audioswitching 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).
4. TV Signal, Control and Teletext Processing
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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 atlater.
First, the control processing stage of the UOC IC will
be examined.
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