Beam Current Sense, DC Restore, Arc Protection, Focus | JVC 340 SC

Chapter 2—Functional Descriptions

Beam Current Sense

The cathode current is sensed at the output of the video amplifier, then filtered and amplified so that the output is a 1mV/1uA signal averaged over several horizontal lines (the number of lines depending on the horizontal frequency). This current sense signal is then sent to the VPB as the signal BEAM.

DC Restore

The DC Restore function is accomplished on the Video Amplifier Board when commanded by the CLAMP signal from the VPB. When the CLAMP signal arrives, the video signal has the offset values (Brightness and Threshold) removed so that they will not be changed by the DC Restore circuit. The CLAMP signal causes the output voltage to be sampled and compared to a reference. The difference is sent to the input of the video amplifier to set the new black level for the duration of the next horizontal line.

Arc Protection

The Arc Protection Circuit functions to drain off any energy that arrives at the Video Output Amplifier board due to arcs on the cathode or grids. The arc energy is suppressed by sending it directly to the HVPS chassis via the Arc Ground terminal on the board.

Blanking

The Blanking circuit operates by using the BLANKING signal from the VPB. The BLANKING signal causes an amplifier to drive an AC coupled pulldown of GRID1. G1 voltage is normally -81V but will be pulled down to -111V during the blanking interval. The cathode voltage is unaffected by blanking.

Enable Circuit

The Enable circuit is controlled by the /ENABLE signal from the VPB. The /ENABLE signal, when pulled high, causes both GRID1 and GRID2 to be pulled low: G1 is pulled from nominal -81V to the disabled value of -200V, G2 is pulled from its usual value of between +800V to +1200V to its disabled value of +15V.

Focus

The FOCUS voltage is a pass through from the HVPS to the CRT. It is not in any way modified by the VOB.

Filament Supply

For the CRT Filament supply, 6.3Vdc from the System PS is simply filtered and sent to the CRT.

2-56	Model 330. 340SC, and 370SC Service Manual

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JVC 340 SC, 330, 370 SC Beam Current Sense, DC Restore, Arc Protection, Blanking, Enable Circuit, Focus, Filament Supply

Contents

Model Model 340 SC Model 370 SC Hughes-JVC Technology Corporation Manufacturer Hughes-JVC Technology Corporation Confidential and proprietary information Safety Equipment Introduction Installation Safeguards Projector Weight Heat Safeguards Light SafeguardsFans Ultra Violet and Infrared Light Viii Ventilation and Foreign Object Retrieval Fluid SafeguardsPower Supply Safety Safety Acronyms Used In Manual Hardware Compatibility SafetyUpdates Software Graphics enhancement Memories Decoder board option Contents Functional Descriptions 1Model 330, 340SC and 370SC System Block Diagrams Cover and Base External Power Requirements Electronics Systems Overview Functional Descriptions System Power System Power Supply STB STB AC Input CRT SCB HDB VDB VPB RTG VAB 4System Power Supply Input/Output Diagram Arc Lamp Ignitor 22-30V depending on projector model High Voltage Power Supply High Voltage Power Supply Functional Descriptions Card Cage Circuit Boards 104668 Backplane Board 100571 Functional Descriptions 10Raster Generation Block Diagram 11Raster Timing Generator Block Diagram Raster Timing Generator Board RTG p/n Sync Generator Sync Detector and Selector Vsync Detector, Field Separator, and Mux Phase Locked LoopSerration and Equalization Lockout Adjustment Counters Serial Communication Information Description Raster Timing Generator I/O System Controller BoardInputs Description Outputs Description Video Processor Board Vertical Deflection Board Interlocks and Protection Horizontal Deflection Board P/N 102523 HDB 12Horizontal Deflection Board Block Diagram Vertical Oscillator Horizontal Centering Horizontal Phase Locked LoopHorizontal Power Supply Output Section Flyback SwitchingGeometric Correction IIC Horizontal Sweep Failure DetectionBus Information Description Horizontal Deflection Board I/O Main Horizontal Deflection Coils Inputs Description Raster Timing Generator Inputs DescriptionVertical Deflection Board Inputs Description Vertical Deflection Board P/N 102521VDB GND Functional Description Vertical Preamps 13Vertical Deflection Board Side Pincushion and Keystone Correction Vertical AmplifiersSweep Failure Detection Horizontal Linearity Correction Top and Bottom Pincushion and Keystone Correction Correction Amplifiers Rxcorr Rycorr Gxcorr Gycorr Bxcorr General I/O Input Description Horizontal Deflection Board Inputs Description System Controller Board Output DescriptionVideo Processor Board Outputs Description Correction Coils System Power SuppliesMain Vertical Deflection Coils Interlocks and Shutdowns Functional Descriptions Video Processor Board P/N 104672 VPB 15Video Processor Board, Block Diagram Decoder Video/Sync Mux Sync StripSG Sync Strip R Brightness and Contrast Amplifiers Gamma Correction On-Screen SwitchSwitch Logic and Video Enable RGB Sensitivity and Threshold Amplifier ILA Bias Dynamic Focus Amplifier IIC Vidok IIC SweepokIIC Beamdet Redbias Rthresh GthreshBthresh Raster Timing Generator External Video Inputs Description Video Amplifier Board Inputs DescriptionVideo Amplifier Board Outputs Description Image Light Amplifiers Decoder High Voltage Power Supply Outputs Description System Power Supply Inputs DescriptionVdfocus Hdfocus Video Amplifier Board P/N 103567 or 103774 VAB Video Signal Failure Detection DC Restore Enable CircuitBeam Current Sense Arc Protection General I/O Output Description High Voltage Power SupplyCRTs System Controller Board P/N 104668 SCB General Functional Description CPU Working and Compressed Memory Expanded Memory Correction Address Generator DACs Overlay Memory Overlay Address Generator Overlay Interface LED Display Buffers and LogicRS232 Interface IR Interface IIC Interface Serial Interface Video Processor Board Description Video Processor Board Output Description Corrstrt Vertical Deflection Board Description Horizontal Deflection Board Dot Matrix Status Display IR Interface RS-232 Interface SignalsBackplane Board p/n CRT Assembly Image Light Amplifier ILA AssemblyOptical Section Relay Lens Functional Description CRT Image Focuses ILAGenerates high intensity light beam Filters infrared light Projection Lens Arc Lamp AssemblyPrism Image Light Amplifier Optical SubassembliesCold Mirror Ultraviolet Filter and Condensing Lens Functional Description Functional Descriptions Service Adjustments Service Cover-Off Power-On Sequence 1Power Interlock Switch and Main Circuit Breaker CRT Yoke Rotation Service Adjustments Vertical Size Tracking Vertical Linearity Tracking Horizontal Size Tracking ILA Bias Settings CRT Mechanical Focus Service Adjustments Service Adjustments Electronic Focus Jumper Settings Front/Rear Jumpers A R Inverted Vertical Jumpers Sensitivity/Threshold Offset 10 G2 AdjustmentG2 Setting Service Adjustments Arc Lamp Alignment and Focus Model 330 Arc Lamp Alignment and Focus Service Adjustments Model 340SC and 370SC Arc Lamp Alignment and Focus Axis Plate Arc Lamp Current Adjustment Model 340SC and 370SC Arc Lamp Adjustments Watts ± 25W Amps Normal Amps Maximum Service Adjustments Maintenance Remove/Replace Before performing any removal and replacement procedures 1Major components of the Model 330 Projector 2Major components of the Model 340SC and 370SC Projectors Projector Covers Ventilation Filters Arc Lamp Assembly Model 330 Ignitor and Arc Lamp Assembly P/N 900611S Removal J503 J504 Ignitor Assembly POS InputNEG Output Interlock Switch Fan Connector Circuit Breaker Collimating Condensing Lens Adjustment Mm Set Screw Mounting Screws System Power Supply To remove the system power supply see -4and -5and Figure Maintenance System and HV Power Supply left side of projector Electronics Module Maintenance Cathode Ray Tube CRT Model 330 CRT Removal Maintenance 10Model 340SC and 370SC CRT Assembly Video Amplifier Board VAB Model 340SC and 370SC CRT Removal CRT Yoke To remove the CRT yoke see -9or Figure High Voltage Power Supply Hvps Card Cage Printed Circuit Boards Image Light Amplifier Assembly Projection Lens 2for reference to part numbers, if necessary SCB Socket Battery Replacement 13System Controller Board Sram Chips Location Recommended Spares Description Quantity 330 340SC 370SC Troubleshooting General Information On-Screen Text Description Power-On Codes First Set Second Set Code Description Break Points Code Meaning Description Resetting the Projector Break Trap Data from the Diagnostics Menu Main Menu Structure Main Menu Problem Possible Solution Service Operator Symptom to Manual Cutoff Check Raster Edge Video image not Correct using P Incushion Squared Adjust Contrast and Brightness No response Set I/R remote dip switch settings Problem Possible Solution Service Operator Symptom to Manual Glossary of Terms CRT Hdtv ISO MTS VHS Secam Freq Vertical Glossary