Progressive Scan& DTV Ready

Projection TelevisionsMain Power Supply

&Complete Shutdown Troubleshooting Guide

TP61G90TP61H95TP71G90TP71H95TW65G80TW65H80

ContentsOverall Block Diagram ......3

Overall block Diagram ............................ 4

Main Power Supply .................. 5Main Power Supply .................................. 6

VIN Terminal (pin 5) - Start Circuit ...... 7

OCP/INH Terminal (pin 4) Function ..... 7

Soft Start ................................................... 8

Surge Protect ............................................ 9

F/B Terminal Voltage (pin 6)/Oscillator/

Constant Voltage Control Circuit ... 10

Latch Block ............................................. 11

Overheat Protection Block (Internal to

Q801).................................................. 11

Overvoltage Protection Block (Pin 5) . 11

Latch Trigger Terminal (Pin 7) ............ 11

Troubleshooting Flowchart................... 12

Sub Power Supply .............13Operation ................................................ 14

Start-up and Over Voltage Protect ...... 15

Logic and Drivers ................................... 16

Oscillator ................................................. 16

Oscillator Control .................................. 17

Latch ........................................................ 17

Thermal Shock Detection Block .......... 18

Over Current Protection ....................... 18

Soft Start ................................................. 18

Resonate Correction .............................. 19

Additional Information .......................... 20

Troubleshooting Flowcharts ................. 21

Shutdown ................................. 23Basic Operation ...................................... 24

Monitoring Circuits ............................... 26

X-Ray Protection .................................... 26

125V Over Current Protect .................. 27

125V Over Voltage Protect ................... 28

Horizontal Stop Protection Circuit ...... 29

21V Over Voltage Protect ..................... 30

35V Over Current Protect .................... 31

+21V Over Current Protect .................. 32

-21V Over Current Protection .............. 33

Troubleshooting Flowchart ................... 34

3

Overall Block Diagram

4

Overall Block Diagram

Figure 1 is an overall block diagram of the standby, main,and sub power supplies in the progressive scan televi-sions. The standby supply is always active whenever thetelevision is plugged into an AC line source. It delivers5V VDD and a reset 5V to the microprocessor to keep itoperational at all times, even when the television is OFF.Transformer T840 isolates the standby supply from thelive ground, and D840 is a full-wave bridge rectifier thatsupplies 15V DC to voltage regulator Q840 and relaysSR81 and SR83 (relay connections not shown). Whenthe microprocessor receives an ON command from theremote control or power key, on the front of the televi-sion, it sends 5V to the relay drivers to close relays SR81and SR83. Closing the relays supplies the AC line inputto the remaining two power supplies to operate the tele-vision.

Troubleshooting Tip:

If both relays never close, check the standby power sup-ply. Both the 5V VDD and the reset 5V are mandatoryfor the microprocessor to operate.

The main power supply and sub power supply work in-dependently from each other, so one supply can be dis-abled to check the other. If the main power supply isdisabled, the television would not have picture or sound,but the microprocessor would still control the relays.Therefore, the sub supply could be turned ON and OFFand its voltages would appear as normal. If the sub powersupply is disabled, everything would work except the pic-ture would be out of convergence. Either power supplycan easily be disabled by removing its fuse: F860 for thesub supply and F811 for the main supply.

16 +125VD808

17

T861

Main Switching IC

Q801

Q804

ErrorAmp.

QB03

PhotoCoupler

D801

Rectifier

140V

Feedback

SR81

Relay

StandbyRegulator

Rectifier & Isolation Trans.

Q840

Microprocessor

QA01

Q841Q842

Relay Drivers

D840T840

3

2

+5-1

5V=Relay On0V=Relay Off

5V

5V

AC LineInput

Standby Supply

Main Power Supply

VDD

Reset18

+8VD811

19 +8VD813

2120

22+35V

D812

12+15V

D810

14+11V

D809

15

T888

Main Switching IC

Q888

Q863

ErrorAmp.

Q861

PhotoCoupler

D861

Rectifier

140V

Feedback

Relay

3

2

9

10

17 D887&

D888

36.5V

13

14

12 D891

D895

21V

-21V

RelayDrivers

Sub-Power Supply

SR83

Q844Q843

F811

F860

5V=Relay On0V=Relay Off

Figure 1. Overall Block Diagram

5

Main Power Supply

6

Main Power Supply

The main power supply is a ringing choke converter. Fig-ure 2 is a block diagram for this supply. An oscillator(OSC) and a switching MOSFET are internal to the mainswitching IC, Q801. During normal operation, D801 rec-tifies the AC line input to approximately 140V. This volt-age is applied to the MOSFET through transformer T862’sprimary winding. As shown in Figure 3a, when theMOSFET conducts, current flows through the T862’sprimary windings and builds an electromagnetic field. Fig-ure 3b demonstrates that after the field builds, theMOSFET opens to stop the current flow through T862.This causes the electromagnetic field to collapse and in-duce current into the secondary windings.

PhotoCoupler

+B

ErrorAmp

OSC

T862

Q801

QB03Q804

125V140V dc

From D801D808

...and an electromagntic field builds.

When the MOSFET conducts, current flows through T862,...

When the MOSFET Stops conducting, the electromagnetic field collapses...

...and current is induced in the secondary windings.

Current Flow

Elecitromagntic Field

PhotoCoupler

+B

ErrorAmp

OSC

T862

Q801

QB03Q804

125V

D808

PhotoCoupler

+B

ErrorAmp

OSC

T862

Q801

QB03Q804

125V

140V dc From D801

D808140V dc

From D801

(a) (b)

Figure 2. Main Power Supply Block Diagram

Figure 3. Main Power Supply Operation

7

VIN

Terminal (pin 5) - Start Circuit

As shown in Figure 4, pin 5 (VIN) of Q801 is the startupand over voltage protect (OVP) for Q801. To start theoperation of the power supply, 140V draws currentthrough resistors R802 and R803 which builds a chargeon capacitor C825. When the charge reaches 22.5V,Q801 starts switching. Once Q801 is operating normally,the ND winding and rectifier diode D805 provide 25V topin 5 to maintain Q801’s switching operation, and C825functions as a filter capacitor.Pin 5 is also used for the over voltage protection (OVP).If the voltage on VIN raises above 28V, an internal latchstops Q801 from operating. Refer to the Latch Blocksection for further details.

StartOVP

R871 T862

C825

D805R803 & R802

Q801

FromD801

25V dc 5 VIN

D806ND

Figure 4. VIN Terminal and Start Circuit

OCP/INH Terminal (pin 4) Function

The OCP/INH terminal is a safety terminal that protectsQ801 if an over current condition develops during op-eration. Figure 5 shows this circuit diagram.

(1) OCP Function (Over Current Protect)When the MOSFET is turned ON, current flowsthrough resistors R827 and R828 and a voltage de-velops at the over current protect (OCP) terminal atpin 4. If the voltage reaches 0.5V, the internal OCPcomparator turns the MOSFET OFF and stops itscurrent flow.

(2) INH Function (OFF Time Control)At the same time the OCP comparator turns theMOSFET OFF, the inhibit (INH) comparator stops

the oscillator and prevents the MOSFET and oscil-lator from operation until the OCP voltage dropsbelow 0.5V. The waveforms for this operation areshown in Figure 6.

R827R828

4

Drive

To T862

Q801

R827

2

1

Oscillator

Latch

0.5V

0.5V

OCP

INH

0.5V

Drive Output

OCP/INH terminalvoltage

Figure 5.Over Current Protect (OCP)and Inhibit (INH) Terminal

Figure 6.OCP/INH Waveforms

8

Soft Start

The soft start circuit prolongs the life of the power supplyby reducing surge current at turn ON. Figure 7 showsthe soft start circuit. When the power supply starts up, aregulator inside Q801 outputs 3.1V on the soft pin 7 (startterminal) that causes current flow through the over cur-rent protect (OVP) resistors (R827 and R828) and re-sistor R811. The additional current flow makes the OCPmore sensitive. The increased sensitivity causes the OCPto trigger earlier than normal and reduces current throughthe MOSFET and T862’s primary windings. Once C818is fully charged, current stops flowing through the OCPresistors and normal operation begins. Figure 8 showsthe effect the soft start circuit has on the MOSFET’s draincurrent during startup.

C818

R811

R827R828

3.1V7

4Over Current Protect

Latch Trigger

Drive

To T862

Q801

R8272

1

Without Soft Start

With Soft Start

Figure 7. Soft Start Figure 8. Soft Start Effect

9

Surge Protect

Refer to figure9. R815 and R816 reduce surge currentthrough the main power supply at startup. They provideadditional resistance on the ground path of rectifier D801.Relay SR85 is disengaged before the supply operates.AC current is applied to rectifier D801 when relay SR81closes. After the supply begins to operate, it producesvoltage sources on the secondary of T861. Two of thevoltage outputs engage SR85. The 15V output suppliesa current source for SR85. The +7V-1 source forwardbiases Q805 to close the relay and provide a direct groundpath for D801 by bypassing R815 and R816.

SR85

Q801and

T861D801

Q805

R826

7V-1

15VRelaySR81

R815

Main Power Supply

R832

D823

Figure 9. Surge Protect

10

F/B Terminal Voltage (pin 6)/Oscillator/Constant Voltage Control Circuit

Refer to Figure 10. Internal to Q801 is an oscillator andoscillator control circuit. The oscillator controls the switch-ing MOSFET in Q801. To control the power supply’sregulation, a feedback signal manipulates the oscillatorfrequency to maintain a consistent current flow throughthe load.Capacitors C2 and C3 and resistor R3 and R2, internalto Q801, determine the MOSFET’s base switching fre-quency. The MOSFET’s OFF time is a fixed value de-termined by R3 in parallel with C3. C2 and R2 deter-mine the maximum duration of the MOSFET’s ON time.

Figure 10. Voltage Control

An external pulse width modulated (PWM) signal, devel-oped by any variance in the load current and coupled tothe power supply’s primary side by a photo-coupler, isapplied to pin 6 (F/B) of Q801 to adjust the chargingtime of C2 as required by the load. If the load currentdecreases, the MOSFET’s ON time increases to com-pensate and increase the output of the power supply. Thelonger the ON time, the larger the electromagnetic fieldbuilds around T862’s primary windings. The larger elec-tromagnetic field induces more current into the secondarywindings when it collapses. On the other hand, if the loadcurrent increases, the ON time decreases to reduce theoverall output of the power supply.

Drive

Latch

C3C2

R3

Oscillator

OCP

6

To 25V VIN

Q803

Q804

R819R817

R818

R813

R814

125V Main B+

R2

Regulator

From Start Block

11

7

4

Drive

To T862

Q801

2

1

0.5V

0.5V

OCP

INH

Latch

C3C2

R3

Oscillator

C1

Start

OVP

TSD

9.9V

3.1V

Regulator

5 VIN Start-up & OVP

6

R827R828

R827

3

To Photo-Coupler

C818

R811

Soft StartTrigger

Drain

Source

Feedback

R2

Latch Block

Refer to Figure 11. A latch internal to Q801 stops Q801’soperation to protect the IC from damage if a problemoccurs. Three conditions trigger the latch circuit: Over-voltage on the Vin (pin5), Q801’s temperature exceeds1250 C, and if the MOSFET’s switching frequency is toohigh. Once the latch triggers, Q801 remains OFF untilthe AC power to the circuit is removed. Q801’s internalcapacitor (C1) is a delay that prevents the latch from en-gaging during startup.

Overheat Protection Block (Internal toQ801)

Refer to Figure 11. Because of the amount of currentflow through the MOSFET, the MOSFET generates heat.

The thermal shock detect (TSD), located internally toQ801, triggers the latch circuit when Q801’s frame tem-perature exceeds 125°C (minimum).

Overvoltage Protection Block (Pin 5)

Refer to Figure 11. The overvoltage protection circuitmonitors the voltage on pin 5 (VIN) of Q801 and engagesthe latch if the voltage rises above 28V. Refer VIN Ter-minal section for further explanation.

Latch Trigger Terminal (Pin 7)

Refer to the Figure below. The SS/Tri terminal (Pin 7) ofQ801 monitors the switching frequency of the internalMOSFET. If the frequency increases excessively, C818conducts and a voltage develops on pin 7. If the voltageon pin 7 reaches 9.9V, the latch shuts Q801 OFF.

Figure 11. Internal Block Diagram of Q801

12

Troubleshooting Flowchart

Notes:This flow chart is to help narrow the

cause of shutdown. Refer to thecircuit explanations for additional

information.

Caution:Before removing or adding fuses,

remove all power from thetelevision and always use a Isolationtransformer when troubleshooting.

Remove fuse F860.

Are pins 1 &2 of Q801

shorted to ground orto each other?

Yes

Replace Q801, CheckR827,R828, & thefeedback circuit.

Does relaySR81 close when the

power button ispushed?

Yes

No

Check the relay drive,microprocessor and stand-by

power supply circuits.

Does +140Vappear at pin 1 of

Q801?

Yes

No

Check R815, D801,C813 &F811

Start

No

Remove fuses F802,F804, F808, F805, &

F806.

Separates the loads from themain supply

Disables the sub-powersupply.

Check D805, D806,R827,R828, C881,

R803,& R802

Connect a 100Wlight bulb to F802's

supply side.

Substitutes the loads.Without a load, the overcurrent protect triggers thelatch.

13

Sub Power Supply

14

Operation

The sub power supply is a current resonance switchingpower supply. It supplies the digital convergence andconvergence boards. Figure 1 is a block diagram for thissupply. The primary winding of T888 and capacitor C870create a LC series resonant circuit. An oscillator (OSC),drive circuit, and two MOSFETs are located internal toswitching regulator Q888 (STR-Z4151). The OSC de-termines the power supply’s switching frequency. Thedrive circuit alternately switches the MOSFETs ON andOFF. The two power MOSFETs, in a push-pull con-figuration, alternate the current flow through the LC cir-cuit during normal operation. The alternating current con-tinually builds and collapses an electromagnetic field aroundT888’s primary windings. The collapsing of the electro-magnetic field induces current into the secondary wind-ings of T888. A full-wave rectifier converts the inducedcurrent into a +21V line and a –21V line.To regulate the secondary voltages, an error amplifiermonitors the +21V line and supplies a negative feedbackto the oscillator through photo-coupler Q861 that iso-lates the primary side of the power supply from the sec-ondary. Refer to Figure 2. The power supply’s switchingfrequency operates above the LC resonance frequency.When the load increases and requires more current, theoscillator frequency decreases and operates closer to theLC resonant frequency. The closer the switching frequencyis to resonance, the more current flows through the pri-mary windings of T888 and the larger the electromag-netic field builds. The larger the electromagnetic field iswhen it collapses, the more current is induced in the sec-ondary winding. When the load decreases and requiresless current, the switching frequency increases and movesaway from resonance. As a result, less current is inducedin the secondary windings.

PhotoCoupler

ErrorAmp

Drive

OSC

T888

C870Q888

Q861Q863

21V

140V from D861

-21V

LoadCurrent

Resonant Freq.

Operating Freq.

SwitchingFreq.

Increased Load

Decreased Load

Normal Operating Freqency is 70-80kHz

Figure 1.Sub Power Supply

Block Diagram

Figure 2.Resonant Frequency

15

Start-up and Over Voltage Protect

Refer to Figure 3. A voltage divider (not shown) uses thepositive cycle of the line input to supply a 16V start-uppulse to pin 9 of Q888 via resistor R861. After start-up,a drive circuit consisting of a secondary winding of T888,diode D864, and capacitor C868 supply 16-20Vdc topin 9 of Q888 to maintain its operation. The voltage de-veloped by the drive circuit fluctuates with the switchingfrequency of the power supply. Therefore, the voltage onpin 9 is also applied to an over voltage protect (OVP)block internal to Q888. If the voltage on pin 9 increasesto 22V, the OVP triggers the latch and switching stops.Refer to the latch block for further information. D876 is a27V zener diode that protects Q888 by preventing ex-cess voltage increases on pin 9.

Figure 3. Start-up

Vcc

StartOVP

R871

T862C868

D864R861

Q888

FromD861

16-20 Vdc 9

D876

16

Logic and Drivers

Refer to Figure 4. The logic block controls the MOSFETs’switching frequency. The outputs of the logic block feedtwo drives that are powered by the start block. After thestart-up voltage is applied to pin 9, the start block sup-plies a drive Vcc (DRI Vcc) of approximately 8V to pin10. Delaying the driver supplies at start-up, preventsdamaging the MOSFETs. The 8V on pin 10 powersdriver B internally. To power driver A, resistor R862 anddiode D862 add the voltage from pin 10 to the voltage onpin 15. D875, C863, D873 and C873 are voltage regu-lators and filters for these supplies.

Oscillator

Refer to Figure 5. Q888’s internal Oscillator developsthe power supply’s switching frequency by generating aramp waveform at capacitor terminal (CT) pin 4. Ca-pacitor C862, connected to pin 4, determines the lowestoscillation frequency. Both MOSFETs are OFF for ashort time when they are alternately switching. This OFFtime is called dead time and determined by resistor R867on the dead time (DT) terminal pin 3. Zener diode D872is a clamp.

Figure 4. Logic and Drivers

VB

Logi

c

COM.

Out

VIN

VccDRI Vcc

A

B

Start

R862 D862

C863D875

C873D873

To T888

Q8889 10 15

12

15

14

B+130V

4DT CT

OSC

R867C862 D872

Q888

3

Figure 5. Oscillator

17

Oscillator Control

Refer to Figure 6. To regulate the power supply, a feed-back signal developed by error amp Q863, on the sec-ondary side of the power supply, feeds the oscillator con-trol circuit at control terminal (CONT) pin 5. Currentflowing through the CONT terminal varies the chargingtime of capacitor C862 (shown in Figure 5). The oscilla-tor control circuit changes the oscillator frequency to main-tain a consistent current flow through the load. Thus, thecurrent through the CONT terminal corresponds to thefeedback from the +21V output. The Fmax resistor R868on pin 6 determines the maximum oscillator frequency.

Latch

Refer to Figure 7. The latch block stops the operation ofQ888 until the voltage on pin 1 of Q888 is removed byturning the television OFF. Any of the following detec-tion blocks can trigger the latch.

• Over voltage protection (OVP) Block• Thermal shock detection (TSD) Block• Over current protection (OCP) Block

The charging time of capacitor C869, connected to thecapacitor delay (CD) terminal pin 8, delays the operationof the latch circuit during start-up.

Figure 6. Oscillator Contol

OSC

R868

5 6Cont. FMAX

OSCControl

Q861

R560Q863

21V Load

B

COut

B+Q862

C881

R895

R883 Q888

G

Figure 7. Latch Block

8CD

TSD OVP

LatchDelay

OC/RC

C869

Q8881 VIN

18

Thermal Shock Detection Block

The thermal shock detection block triggers the latch ifQ888’s internal temperature exceeds 150°C.

Over Current ProtectionRefer to Figure 8. The over current detect (OC) sensesexcess current in the LC series resonant circuit. As cur-rent in the LC series resonant circuit increases, a voltagedevelops at the over current protect (OC) terminal pin11. Resistor R870 and C874 detect the current flowthrough the LC circuit. Resistor R866 samples the volt-age and applies it to pin 11. Capacitor C867 is a filter toreduce ripple. Depending on the input voltage, the overcurrent protect responds in one of two ways:

(1) OC Low Threshold Voltage: +1.8VWhen the input voltage at the OC terminal is higher

than +1.8V, the voltage at the soft start (Css) terminal pin7 lowers and the soft start engages. By reengaging thesoft start, the main oscillator frequency increases reduc-ing the current flow through the LC circuit. The soft startcontinues to operate until the voltage on pin 11 dropsbelow 1.8V.

(2) OC High Threshold Voltage: +2.5VIf the input voltage at the OC terminal exceeds

+2.5V, the oscillator frequency increases to its maximumfrequency and C866 discharges rapidly. When the Cssterminal voltage decreases to 0.7V, the circuit resets andC866 charges again. The main oscillator frequency de-creases gradually. If this condition continues, the latchengages and oscillation stops.

Soft Start

Refer to Figure 8. At start-up, the soft start is engagedby capacitor C866 on pin 7, soft start (Css) terminal.While capacitor C866 charges, the switching frequencyincreases to reduce surge current through the MOSFETs.Once C866 is fully charged, the switching frequency goesto its normal operating frequency (approximately 70-80kHz).

Figure 8. Over Current Protect

7

11OC

Css

OC/RC

Q888

T888

C870R870C867

To pin 14, Q888

To MOSFET (B)

C866

R866

R872

140V B+

OSCOSCControl

C874

19

15 VB109

Logic

1

14

12

27 5 6 3 4

8

11

CD

OC

Css Cont. FMAX DT CT GND

COM.

Out

VIN

Vcc DRI Vcc

TSD OVP Start

Ref.LatchDelay

OSCOSCControlOC/RC

A

B

ToR861

Outto VB

From DRI Vcc

FromC866

FromR864 From

R868

FromR867From

R862

FromR866

FromC869

Q888

Resonate Correction

Figure 9 shows the internal block diagram of Q888. Bymonitoring MOSFET B’s gate, the over current protectblock (OC) prevents the oscillator switching frequencyfrom dropping below the LC resonate frequency.

Figure 9.Internal Block Diagram of Q888

20

Pin Name Vdc Description1 VIN 140 Half bridge power input2 GND 0 Control unit ground3 DT 6 Dead time resistor terminal4 CT 2.4 Oscillator capacitor terminal5 CONT 5.9 Oscillator control terminal6 FMAX 6.2 Maximun frequency resistor terminal7 Css 3.7 Soft start capacitor terminal8 CD 0.4 Delay latch capacitor terminal9 VCC 18 Control unit power terminal

10 DRI 8 Gate drive power output11 OC 0.7 Out of resonance / over current detection12 COM 0 Half bridge GND14 OUT 71 Half bridge output15 VB 78 High side gate drive power input

On Off On

Off On Off

C870 140 Vpp

Pin 4, Q888

Pin 14, Q888 160Vpp

Internal Q888MOSFET (B)

Internal Q888MOSFET (A)

Dead TimeInternal Q888

1.5 Vpp

Additional Information

Caution: Different input signals may cause a variance in voltage readings. The voltages and waveforms below wererecorded while displaying a color bar signal.

21

Troubleshooting Flowcharts

Remove fuse F811.

Does aconstant voltageappear at F863's

supply side?

Yes

Connect a 100Wlight bulb to F470's

supply side.

Does relaySR83 close when the

power button ispushed?

Using the isolatedground, check the

voltage on the powersupply side of fuse

F863.

Yes

No

Check the relay drive,microprocessor and stand-by

power supply circuits.

Does thevoltage regulate

at 21Vdc?Yes

The power supply isoperating normally.

No

Check: Feedback Circuit: Q862,Z801Resonate Capacitor: C870Over Current Protect: R865,R870Soft Start: C866

Does thepower supply make

a soft "tick-tick"sound?

No Yes

Check Drive Circuit:D864,R871 and C868.

Start

No Turn to next page.

Remove fuses F861,F863 and F864.

Disconnects the loads on secondary side

Disables main power supply

Caution:Before removing or adding fuses,

remove all power from thetelevision and always use a Isolationtransformer when troubleshooting.

22

With fuse F863 still open,check the voltage on the powersupply side of F863 when thetelevisions is first turned on.

Does thevoltage at F863 rise

to >21V then drop, or doesthe voltage never

appear?

Voltage never appears.

Voltage appears then drops.

Using thelive ground, checkfor 140V on pin 1

of IC888. No voltage.Voltage is present.

Check: Fuse F8860. If open, replace Q888.Rectifier: D861Filter Capacitor: C857

Check: Oscillator Terminal: C862, D872DRI Circuit: D862, R862, D875Start-up:R861,D876Latch Delay Capacitor: C869

Check: Feedback: Q861,Q863,D881

Continued from theprevious page.

Caution:Before removing or adding fuses,

remove all power from thetelevision and always use a Isolationtransformer when troubleshooting.

23

Shutdown

24

Basic Operation

The shutdown circuit is a safety device that bypasses themicroprocessor to turn OFF the relays (SR81 and SR83not shown) if certain problems occur in the television. Asshown in Figure 1, The protect circuit’s main componentis the silicon controlled rectifier D846 (SCR). The SCRhas an anode and cathode like a diode and a gate thatacts like an ON switch. When 0.825V appears on D846’sgate, current flows through its anode-cathode junction inthe same direction as a standard diode. Removing thevoltage from the D846’s gate does not stop the anode-cathode current flow. Once the anode and cathode con-duct, they continue to conduct even after the gate voltageis removed. Removing the current flow between the an-ode-cathode resets the SCR.10 monitoring circuits in the television can send the nec-essary voltage to the SCR’s gate to start the SCR’s an-ode-cathode current flow. When the SCR conducts, tran-sistor Q845 turns ON and its collector voltage drops closeto ground. Q845’s collector applies this potential to therelay drivers to turn them OFF and disengage the relays.The microprocessor senses that the relay drivers are OFFand blinks the power LED every half-second to indicatea shutdown condition. Unplugging the television resetsthe SCR.

Troubleshooting tip:Because of the speed of the shutdown circuit, techniciansmay have difficulties getting proper voltage readings whenthis circuit activates. A peak response or min/max meteris necessary for troubleshooting a shutdown problem.These meters can read a voltage in a split second andstore the reading into memory for easy recovery. If apeak-response meter is not available, try using an oscillo-scope on the dc setting. The scope reacts quicker thatthe digital voltmeter, and the change in dc level can beseen on the scope’s CRT. However, most scopes do nothave a dc voltage readout or the ability to record the value.The lack of these features makes getting an accurate dcvoltage reading difficult. Therefore, the peak-responsemeter is the preferred method for measurement.

Caution:Always use an isolation transformer when troubleshoot-

ing televisions.

25

Figure 1.Overall Block Diagram

+15V OVPD817-21V OCPR7756Q762

Anode

GateCathode

From +5V

R846

R847

Sub Power SupplyRelay Drivers SR83

Main SupplyRelay Drivers for SR81

Microprocessor

R845

Q845

5V Relays ON0V Relays OFF

OVP = Over Voltage ProtectOCP = Over Current Protect

+21V OVP D892 H. Stop 1D438Q432

H. Stop 2D454Q452

+125V OCPR4039Q492

+21V OCPR7750Q759

+125V OVP+35V OCPR371Q370

D818D819

D490

D820

D439

D371

D7701

D891

0.7 V = Shutdown0 V = Normal

6

7

QA02

X-Ray Q429Q430

D473

D846SCR

26

Monitoring Circuits

Knowledge of each monitoring circuit’s operation and theconditions that trigger shutdown are necessary to find thecause of a shutdown condition. The following circuit ex-planations describe the operation of each monitoring cir-cuit, give a test point for each circuit, and provide trouble-shooting tips to help repair the TV. All voltage readings inthe accompanying illustrations are for normal operationunless otherwise stated. Use the troubleshooting flow-chart at the end of this section to help determine whichmonitoring circuit is causing shutdown and the followingcircuit explanations to understand the circuits operation.Please take note: The troubleshooting tips and flowchartsin the following sections are intended as a troubleshootingguide, NOT an answer to all situations.

Warning!!

Toshiba does not recommend disconnecting the shutdowncircuit for troubleshooting. Disconnecting the shutdowncircuit increases the possibility of a failure causing dam-age to the television.

X-Ray Protection

Figure 2 demonstrates the x-ray protection monitoringcircuit that triggers shutdown if it detects excessive x-rayradiation, which is produced by an increase in high volt-age. T461’s secondary winding across pin 9, diodeD471, and capacitor C471 produce a DC voltage di-rectly proportional to the high voltage (HV). A resistordivider consisting of resistors R451, R452, and R453reduces the voltage and applies it to the emitter of Q430.As the high voltage increases, the voltages at C471 andon the emitter of Q430 increase proportionately. Con-nected to the Q430’s base is zener diode D472. If thevoltage on the emitter is large enough, D472 conductsand turns Q430 ON. Q430’s conduction increases thevoltage on its collector to turn Q429 ON. When Q429turns ON, current flows between its emitter and collec-tor, and a voltage appears on its emitter. This voltage isapplied to the SCR (D846). The SCR turns ON andshuts the television down. Use the D473’s anode as thetest point for troubleshooting.

Troubleshooting Tips:

Problems with the horizontal outputs, resonance capaci-tors, flyback transformer, deflection yokes, or a shortedCRT may trigger shutdown. Refer to the service manualpart numbers, part values, and schematic diagrams.

• The CRTs are the most likely culprit of an x-ray pro-tection shutdown. Each CRT can be disconnectedseparately by disconnecting the drive PC board. Thetelevision can operate with one of the CRTs discon-nected without damaging the remaining CRTs or tele-vision. A CRT may intermittently arc and cause in-termittent shutdown. LIGHTLY tapping on the neckof the CRT may duplicate this symptom. Take cau-tion when tapping. Tapping too hard can damage theCRT’s neck.

• A shorted secondary winding of the flybacktransformer or distributor block can increase the highvoltage. A ringing check may indicate a bad flybacktransformer; however, replacement of the flybacktransformer or distributor block may be necessary todetermine unequivocally if they are defective.

Figure 2. X-Ray Protection

R448

T461

D471 R451

R453

R450

Q430

D472

Q42912V D473

To SCR'sGate

R454

C471

R4529

0V Normal2.5 V Shutdown>

6V

6.1V

0V

27

125V Over Current Protect

As shown in Figure 3, resistor R4039 is the over currentprotect (OCP) sensing resistor that monitors the currentflow through the 125V line. During normal operation,Q492 is turned OFF and its collector voltage is 0V. Anincrease in current through the load increases the voltagedrop across R4039. If the current increases enough, thevoltage across R4039 forward biases Q492 and turns itON. When Q492 turns ON, its collector voltage increasestowards the supply voltage. To trigger shutdown, resis-tor R4043 supplies the collector voltage to D846’s gatethrough zener diode D491 and diode D490. Use theD491’s anode as the test point for troubleshooting.Capacitor C498 is a delay that prevents surge currentfrom triggering the shutdown when the television is firstactivated.

Troubleshooting Tips:

Either a shorted horizontal output, high voltage output,flyback transformer, or the horizontal output’s resonancecapacitors can pull excessive current through R4039 andcause the 125V OCP to trigger shutdown. Other possi-bilities are: improper power supply regulation or R4039increasing value.

• To check the main power supply, refer to the MainPower Supply troubleshooting chart within the MainPower Supply section of this module.

• A shorted horizontal output or high voltage outputtransistor (Q404 and Q416 not shown) is the mostlikely culprit of this problem. However, a shortedflyback transformer, arching in a CRT, or a shortedyoke my have caused one of the outputs to short. Aringing test can indicate a short in a yoke or a flyback’swinding. Nevertheless, replacement of the yoke andtransformer might be necessary to determine the failedpart. For tips on troubleshooting the CRT, resonancecapacitors, and anode caps, refer to the x-ray pro-tect circuit in the previous paragraphs.

• Lastly, the over current sensing resistor R4039 canslightly increase in value and cause a false shutdownintermittently or at turn ON when the high voltagefirst develops.

0V Normal2.5 V Shutdown>

Load

Q492

R4040

R4039

R4041

To Gate of D846D491 D490

R4038

C497

Main PowerSupply

125V

R4042C498

Figure 3. 125V Over Current Protect

28

125V Over Voltage Protect

The 125V over voltage protect (OVP), shown if Figure4, monitors the 125V supply and triggers shutdown if thevoltage increases excessively. If the supply voltage risesabove D818’s zener voltage, the diode conducts and de-livers a logic HIGH (approximately 2.5V or higher) to theanode of diode D819 which applies the voltage to D846’sgate to trigger shutdown. Normal voltage at the anode ofD819 is about 0V. A voltage of 2.5V or GREATER atthis point results in shutdown. Use a peak-hold meter atthis point for troubleshooting.

Troubleshooting tip

A supply voltage increases when there is a loss of load.However with this supply, a loss of load will not increasethe supply voltage enough to trigger the OVP. If the OVPis triggering shutdown, the main power supply is produc-ing excessive voltage. Usually, a loss of feedback in thepower supply circuit causes an increase in the supply’soutput voltage. Refer to the Power Supply Section ofthis module for more information on the main power sup-ply.

LoadT861

D808

C832Solder Link

R820

D818 (30V) D819

To Gate of D846.

0V Normal2.5 V Shutdown

+125V

>

R822, R830,&R831

R824

Figure 4. 125 Over Voltage Protect

29

Horizontal Stop Protection Circuit

Because the horizontal deflection and the high voltage cir-cuit operate separately, the high voltage circuit can stillproduce an output if the defection circuit fails. If this sce-nario happens, one bright vertical line would appear onthe screen and burn the phosphors of all three CRTs.However, to prevent the vertical line from damaging theCRTs, two horizontal stop protection circuits engage theshutdown circuit and blank the picture if a loss of deflec-tion occurs. Refer to Figure 5 for the following explana-tion of the first horizontal stop circuit. T462 is the hori-zontal deflection transformer. During normal operation,current is induced into the secondary windings betweenpin 3 and 1. Diode D451 rectifies the current, and ca-pacitor C466 filters it to produce a DC voltage that resis-tor R490 applies to the base of transistor Q451. Q451’semitter connects to the base of Q452. During normaloperation, both of these transistors are ON, makingQ452’s collector voltage approximately 3.6V. If hori-zontal deflection is lost, the voltage applied to the base ofQ451 drops and both transistors turn OFF. The voltageon the collector of Q452 increases to 10.8V, and diodesD454 and D439 apply the voltage to the gate of SCRD846 to shutdown the television. Q452 also applies thecollector voltage to the blanking circuit to blackout thepicture and protect the CRTs. Figure 6 shows the sec-ond horizontal stop circuit that works in the same manner

as the first horizontal circuit.Transistor Q441, capacitor C450 and diode D440 pre-vent the shutdown circuit from engaging when the televi-sion is first turned ON. At turn ON, the 12V appearsbefore the horizontal deflection is fully operational. Dur-ing this time, Q452 is OFF and 10.8V appears on itscollector to engage the blanking circuit. Normally thisvoltage would also engage the shutdown. But when thepower is first applied, capacitor C450 charges and al-lows current to flow through Q441’s base – emitter junc-tion to turn it ON. While Q441 is ON, its collector volt-age is at ground which prevents the 10.8V application tothe SCR. Once C450 reaches its full charge, Q441 turnsOFF. By this time, horizontal deflection has started andthe circuit is operating normally.

Troubleshooting tip:

The television uses two horizontal stop circuits to pervertdamage if T462 shorts. If one of the horizontal stop cir-cuits is causing shutdown, check T462 for shorted wind-ings.

R419

T462

D451

R490Q452

12V To Blanking Circuit

To D846 Gate

Q411

Q451R495R496

R494R493

C446

D440

C450From

H. Stop 2

D439D454(7.5V)

D452D456(7.5V)

0V Normal2.5 V Shutdown>

3.6V

3.6V

4.2V8.7V

9.3V

D453

3

1

Figure 5.1st Horizontal Stop Protect

30

R431

T462

D431

R432Q432

12V To Blanking Circuit

To D846 Gate

Q411

Q431

D433

R435R436

R437R434

C415

D440

C450 From H. Stop 1

D439D438(7.5V)

D432D436(7.5V)

0V Normal2.5 V Shutdown>

3.6V

3.6V

4.2V8.4V

9.1V

6

5

Figure 6.2nd Horizontal Stop Protect

21V Over Voltage Protect

The 21V over voltage protect (OVP) monitors the 21Voutput of the sup power supply and triggers shutdown ifthe voltage increases excessively. Refer to Figure 7. Ifthe supply voltage rises enough to break D892’s zenervoltage, the diode conducts and delivers a logic HIGH(approximately 2.5V or higher) to the anode of diodeD891 which applies the voltage to D846’s gate to triggershutdown. Normal voltage at the anode of D891 is about0V. A voltage of 2.5V or GREATER at this point resultsin shutdown. Use a peak-hold meter at this point fortroubleshooting.

Troubleshooting tip

A supply voltage increases when there is a loss of load.However with this supply, a loss of load will not increasethe supply voltage enough to trigger the OVP. If the OVPis triggering shutdown, the sub power supply is producingexcessive voltage. Usually, a loss of feedback in the powersupply circuit causes an increase in the supply’s outputvoltage. Refer to the Sub Power Supply Section of thismodule for more information on the sub power supply.

Figure 7. 21 Over Voltage Protect

Load

T861 D897

Solder Link

D892 (22V) D891

To Gate of D846.

0V Normal2.5V Shutdown

+21V

>

R893

D898

31

35V Over Current Protect

The +35V over current protect (OVP) monitors the cur-rent through the +35V line which is developed by themain power supply and supplies the vertical output Q301and other transistor switching circuits. As shown if Fig-ure 8, current flows through the current sensing resistorR370. If the load current becomes excessive, the voltagedrop across R370 increases and turns ON transistorQ370. When Q370 turns ON, the collector voltage in-creases towards the +35V supply and Zener diode D370conducts to deliver a voltage the gate of SCR D846. Usethe peak-response meter on D371’s anode of for a testreading.

Troubleshooting Tips:

A shorted vertical output Q301 is the likely causes ofexcessive current draw from the +35V line. If the verticaloutput fails, usually, pins 1 and 2 or 1 and 6 short to-gether.

0V Normal2.5 V Shutdown>

Load

Q370

R372

R370

R373

D370 D371

+35V

R371

Main PowerSupply

To D846 Gate

Figure 8. 35V Over Current Protection

32

+21V Over Current Protect

Figure 9 is the circuit diagram for the +21V over currentprotect (OCP). Resistor R7750 is the over current sensingresistor that monitors the current flow to the convergenceoutputs (Q751 and Q752 not shown). An increase incurrent increases the voltage drop across R7750. Duringnormal operation, transistors Q759 and Q758 are turnedOFF and transistor Q757 is ON. Because Q757 is turnedON, the voltage at its collector is 0V. A slight increase inthe voltage across R7750 turns ON Q759 and increasesits collector voltage. Then, Q758 turns ON, and itscollector voltage drops to ground and turns OFF Q757.The emitter-collector current of Q757 stops and thevoltage on the collector rises to a logic HIGH(approximately 2.1V or higher). The logic HIGH isapplied to the gate of the SCR D846 through D7701,and shutdown takes place. Because transistor Q757 isalso controlled by -21V over current protect, the collectorof Q759 should be used as the test point. A voltage of5V or GREATER at this point indicates the transistor isturning ON and activating shutdown.Transistor Q783 is always slightly foreword biased toreduce the sensitivity of the shutdown circuit and preventfalse shutdowns.

Troubleshooting Tips:

• The over current sensing resistor can increase in valueand cause a false or intermittent shutdown. Makecertain the current sensing resistor is the proper value.

• If excess current is pulled from the power supply,check the convergence output ICs (Q752 and Q751located on the convergence output PC board) andthe surrounding biasing resistors. The digitalconvergence board can cause the Q752 and Q751to work too hard and pull excess current. If this issuspected, remove the digital convergence board fromthe television with the television unplugged. Plug thetelevision back in and turn it ON if necessary. If thetelevision comes ON*, the digital convergence boardmay be bad. If the television still shuts down, Q752,Q751, or their surrounding biasing circuits may bebad.

* The television can power up without the digital conver-gence board in place, but the television will be out of con-vergence. The raster bows in from all sides because thehorizontal and vertical scanning are not going all the wayto the end of the CRTs. Do not let the television run foran extended time in this condition. If left in this conditionlong enough, it can burn the phosphorous. If additionaltesting is required in this condition, turn the contrast andbrightness all the way down to reduce the risk.

Figure 9. +21 Over Current Protect

To D846'sGate

0V Normal5 V Shutdown>

Load

Q759

C7760

R7749R7751

R7750

R7747

R7742

D7701

+21V

Stand by+5V

Q758

Q757R7745

Sub PowerSupply

Q783R7703

R7704

R7701

R7702

From -21V OCP

7.7V

0.6V1.2V

33

-21V Over Current Protection

The –21V OCP operates in the same manner as the +21OCP. Refer to Figure 10 and the explanation for the +21OCP for details.

Figure 10. – 21V Over Current Protect

To D846'sGate

0V Normal-5 V Shutdown>

Load

Q762

C7763

R7764R7763

R7765

R7758

R7742

D7701

-21V

Stand by+5V

Q761

Q757R7745

Sub PowerSupply

Q784R7752

R7753

R7705

R7706

From +21V OCP

11

34

Troubleshooting Flowchart

Remove fuses F863 & F864.

Yes

No

Check the +21V OCP & -21V OCP

Check the 125V OVP, 125V OCP

+21V OCP

Start

Notes:This flow chart is to help narrow the

cause of shutdown. Refer to thecircuit explanations for additional

information.

With F804 open, the television may power up but not have a

picture. This does not mean the television is still in shutdown.

Shutdown is indicatedby the relays disengaging

after closing, and that the power cordmust be unplugged and plugged back

in for the relays to reengage.

Key:OVP = Over Voltage ProtectOCP = Over Current Protect

Yes No

Apply powerto the TV. Does it still

shutdown?

Caution:Before removing or adding fuses,

remove all power from thetelevision and always use a Isolationtransformer when troubleshooting.

Remove fuse F804.

Apply powerto the TV. Does it still

shutdown?

Check the H. Stop 1, H. Stop 2,

+15 OVP, & X-Ray protect

With F804 still out of circuitRemove fuse F806.

Apply powerto the TV. Does it still

shutdown?Yes No

Check the +35V OCP