Toshiba TW40F80 manual Over Current Protection Circuit

Page 80

8. OVER CURRENT PROTECTION CIRCUIT

8-1. Outline

If main power (125V) current increases abnormally due to components failure, there is possible danger of the second- ary damage like failure getting involved in other part fail- ure, and abnormal heating. To prevent this, over current pro- tection circuit is equipped, which detects current of main B line to turn off power relay in abnormal situation.

8-2. Operation

Fig. 9-24 shows over current protection circuit. When the current of main B line increases abnormally due to the shortage in load of main B line, voltage drop arises across R470. By this voltage drop, when base-emitter voltage of Tr8 in protector module (Z801) becomes approx. 0.7V or more, Tr8 turns on, and the voltage by divided ratio of R15 and R16 is applied to cathode of ZD4. When this voltage becomes higher than zener voltage of ZD4, ZD4 turns on to supply base current to base of Tr6 via R14. This causes Tr5 ON and voltage at pin 16 of Z801 becomes low.

Therefore, QB30 and Q843 turns off to set SR81 OFF. Tr6 and Tr7 in Z801 are in thyristor-connection, and power 5V- 1 supplied at pin 15 keeps protection operation for standby power until main power switch is turned off. During circuit operation, power LED near main power switch blinks in red.

Caution:

• To restart TV set, repair failure first.

5V

MICON

QA01#7

RELAY

SR80

Q845

 

 

 

 

 

F470

R470

 

 

 

 

To T461

 

 

MAIN B

 

 

 

 

 

R471

R479

 

 

 

 

 

 

 

C472

 

 

 

15

 

 

2

1

 

 

R9

 

 

 

 

 

 

 

 

ZD4

R16

 

 

 

 

R10

 

 

 

 

 

 

Tr7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R14

R15

D1

Tr8

 

 

 

 

 

 

 

16

Tr6

 

 

 

 

 

 

Q846

 

R12

C1

 

 

 

 

 

 

 

 

 

 

 

Tr5

 

 

 

 

 

 

 

 

R11

 

 

 

 

 

 

 

 

 

 

 

Z801

 

 

 

 

 

 

PROTECTOR MODULE

 

17

 

 

 

 

 

 

Fig. 9-24 Over current protection circuit

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Contents TW40F80 Contents Terminal FUNCTION, Description and Block Diagram Wide Aspect Conversion Circuit Failure AnalysisSection X Deflection Distortion Correction Circuit Section XI Digital Convergence CircuitSection Feature Improved ServiceabilityOutline Merits of BUS System Reduction of Parts CountSpecifications Chassis ModelFront View Video 3 InputsRear View IN-VIDEORemote Control View 100Chassis Layout Starsight Newosd FRO. SurrConstruction of Chassis Major Features Section II TUNER, IF/MTS/S. PRO Module Circuit BlockOutline RF AGCAudio Multiplex Demodulation Circuit A.PRO block diagram A.PRO Section Audio ProcessorConfiguration of the audio circuit and signal flow are given POP Tuner Terminal No NameOperation of Channel Selection Circuit Microcomputer SDA SCLMicrocomputer Terminal Function Microcomputer Terminal Name and Operation Logic Terminal Name Function In/Out Logic RemarksSDA On Screen FunctionEEPROMQA02 System Block Diagram Local KEY Detection Method Local key assignment FunctionTo TV set Remote Control Code AssignmentCode Function Custom codes are 40-BFH TV set for North U.S.A Code Function Optional Setting for Each Model OPT0 OPT1 Models HEXService Adjustment Entering to Service ModeTest Signal Selection Executing Self Diagnosis Function Failure Diagnosis ProcedureContents to be Confirmed by Customer Understanding Self Diagnosis Indication Self CheckClearing method of self diagnosis result YES Troubleshooting ChartTV does Not Turned on No Acception of KEY-IN No Picture Snow NoiseMemory Circuit Check No Indication On ScreenSection IV DVD Switch Circuit DVD Switch Block Diagram Outline Configuration Section V WAC Circuit OutlineCircuit Operation OperationWide aspect conversion unit block diagram PB6348 Pin Function Pin function of TC9097F QFP 80 pinNames and functions of TC9097F Name FunctionVFL2 Block Diagram TC9097F system block diagramWide Aspect Conversion Circuit Failure Analysis Procedures E2PROM OK?Adjustment Method Raster Horizontal OneScreen multi-search process Section VI Dual Circuit OutlinePrinciples of Operation System Component Diagram of Dual Unit Video/Color/Deflection Process Section OSD Sub Screen Process Section Sub screen process sectionMain/Sub Screen Superimposing Section Main/Sub screen superimposing sectionMain IC Terminal FUNCTION, Description and Block Diagram DiagramQY01 MPC1832GTQY01 mPC1832GT pin layout QY03 TC9092AF internal block diagram QY03 TC9092AF pin layout QY03 TC9092AF pin list No Pin name Pin function CKWMRD1 QY10/QY11 M518221-30ZS internal block diagram Circuit Description Section VII 3-DIMENSION Y/C Separator Circuit OutlineConfiguration Circuit Description Terminal description PZ01 Section Viii Vertical Output Circuit Outline Theory of OperationOutput Circuit Actual CircuitSawtooth Waveform Generation Circuit OperationOutput Output stage power supply voltage Linearity Characteristic Correction Protection Circuit for V Deflection StopCharacter Correction Up-and Down-ward Extension Correction Up-and Down-ward Linearity Balance+35V Over Current Protection Circuit Theory of OperationUZ22BSD UZ11BSBRaster Position Switching Circuit KetsuSignal Section IX Horizontal Deflection Circuit OutlineHorizontal Drive Circuit Basic Operation of Horizontal DriveOn period OFF period Signal DEF/POWER PCB Horizontal Output CircuitOperation of Basic Circuit FBTDescription of the basic circuit T1~t2 T2~t3T3~t4 T4~t6Curve Correction S Capacitor Amplitude CorrectionLinearity Correction LIN Left-right Asymmetrical Correction LIN coil Linearity coilWhite Peak Bending Correction Circuit OutlineOperation Theory EHTBlanking Low Voltage Protection Gate ProtectorHigh Voltage Generation Circuit AFCABL High Voltage DPC Circuit RegulatorHigh Voltage 1. +210V2. +35V Anode High Voltage CircuitCR-BLOCK ED’ ActualFBT CR-BLOCK E H RAY Protection Circuit 23 X-RAY protection circuitOver Current Protection Circuit Functions and Features Block DiagramDiode Modulator Circuit OUTActual Circuit First Half Scanning Period Basic Operation and Current PathLater Half Scanning Period P.T Later Half of Flyback PeriodFirst Half of Scanning Period Section XI Digital Convergence Circuit Outline Reset MemoryProm PLLPicture Adjustment Service Mode Entering/Exiting ModeSfull Initial screenFirst screen Second screen Key function of remote control unit ENTNormal/Full Operation procedureEach Screen Adjustment Method Theater Wide1 Theater Wide 269.5 Case Study When CRT is ReplacedWhen Convergence Unit is Replaced Adjusting Procedure in Replacing Convergence Unit/Main Def TroubleshootingAdjusting Procedure in Replacing CRT Convergence Output Circuit Convergence Block Diagram Convergence Troubleshooting Chart Main Unit
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