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

Models: 340 SC 370 SC 330

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Beam Current Sense

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

DECLARATION OF CONFORMITY Hughes-JVC Technology CorporationSERVICE MANUAL Model Model 340 SC Model 370 SCManufacturer Hughes-JVC Technology Corporation Confidential and proprietary informationSafety Information Safety EquipmentIntroduction Warnings and CautionsInstallation Safeguards Projector WeightHeat Safeguards Light SafeguardsFans Ultra Violet and Infrared LightUltraviolet radiation, dangerous glare, and high internal gas pressure Fluid Safeguards Power SupplyVentilation and Foreign Object Retrieval PowerSafety Model 330, 340SC, and 370SC Service ManualSafety Model 330, 340SC, and 370SC Service Manual1.0 Introduction 1.1 Acronyms Used In Manual1.2 Safety 1.3 Updates1.4 Hardware Compatibility Model 330, 340SC and 370SC Service ManualVideo Amplifier Board Contents 2.0 Functional Descriptions2.1 Cover and Base 2.2 External Power Requirements 2.3 Electronics Systems OverviewThe Model 330, 340SC and 370SC Electronics System consists of 2.4 System Power System Power SupplyFigure 2-2 Backplane Status Indicators ∇ Model 330. Model 340SC = +25V/80a Model 370SC = +30V/100a 2. +24V Standby and Arc Lamp power supplies turn on Arc Lamp Ignitor 22-30V depending on projector model High Voltage Power Supply High Voltage Power Supply Power and Control ConnectorModel 330, 340SC, and 370SC Service Manual Pins 1,4,5,10 not usedCRT anode voltages are not user controllable. They are fixed at 32KV with a maximum output of 2.1mA total or 0.7mA per CRT. The anode voltage is the primary acceleration voltage for the CRT. Other bias voltages screen grid, G2, and control grid, G1 are used to control the level of beam current. The anode voltage is routed out of the top of the HVPS, into the CRT housing to three 3 bulkhead connectors. From there, the anode wires on the CRTs route the anode voltage directly to the CRT. The anode voltages are overvoltage and overcurrent protected in the event of short circuits or CRT arcing 2.5 Card Cage 2.6 Circuit Boards Description340SC 370SC2-16 Model 330, 340SC, and 370SC Service ManualChapter 2-Functional Descriptions Figure 2-10 Raster Generation Block Diagram Model 330, 340SC and 370SC Service ManualChapter 2-Functional Description 2-17Raster Timing Generator Board RTG p/n Sync Generator Sync Detector and SelectorVSYNC Detector, Field Separator, and Mux Phase Locked LoopSerration and Equalization Lockout Adjustment Counters Description Serial CommunicationInformation Raster Timing Generator I/O IICCLKHorizontal Deflection Board Interlocks and Protection Horizontal Deflection Board P/N 102523 HDBSystem Power Supply InputsVertical Oscillator Horizontal Centering Horizontal Phase Locked LoopHorizontal Power Supply Output Section Flyback SwitchingGeometric Correction Horizontal Sweep Failure Detection Serial CommunicationInformation DescriptionHorizontal Deflection Board I/O Raster Timing Generator Vertical Deflection Board P/N 102521VDB System Power SupplyInterlocks and Protection InputsVertical raster centering Top and bottom pincushion correction Vertical Preamps Side Pincushion and Keystone Correction Vertical AmplifiersSweep Failure Detection Horizontal Linearity Correction Top and Bottom Pincushion and Keystone CorrectionRXCORR RYCORR GXCORR GYCORR BXCORR Correction AmplifiersSerial Communication General I/O InformationDescription System Controller BoardSystem Controller Board Outputs Interlocks and Shutdowns InputOutput Internal2-42 Model 330, 340SC and 370SC Service ManualChapter 2-Functional Descriptions Video Processor Board P/N 104672 VPB Decoder Video/Sync Mux V & H Sync StripSG Sync Strip B, G, and R Brightness and Contrast AmplifiersGamma Correction On-Screen SwitchSwitch Logic and Video Enable RGB Sensitivity and Threshold Amplifier ILA Bias Dynamic Focus AmplifierSerial Communication InformationGeneral I/O System Controller BoardInput DescriptionSystem Controller Board OutputsDescription Raster Timing GeneratorVertical Deflection Board Image Light Amplifiers OutputsDescription DecoderHigh Voltage Power Supply System Power SupplyInterlocks and Protection OutputsInternal Video Amplifier Board P/N 103567 or 103774 VABOutput Video Signal Failure DetectionDC Restore Enable CircuitBeam Current Sense Arc ProtectionThis section provides a comprehensive description of the inputs to and outputs from the VAB. The I/O description are arranged by the source/destination of the signal and so the assemblies communicated with are used as the primary heading of each group of signals and then are further subdivided into inputs and outputs. In each case, the signals direction is noted, with input referring to an input to the VAB, and output to an output from the VAB e.g. under Video Processor Board Input CLAMP refers to the signal CLAMP that is an input to the VAB from the Video Processor Board. When test points are provided for the I/O they are noted General I/OVideo Processor Board System Controller Board P/N 104668 SCB System Power SupplyInputs DescriptionGeneral Functional Description Page Working and Compressed Memory Expanded MemoryCorrection Address Generator DACsOverlay Memory Overlay Address GeneratorOverlay Interface LED Display Buffers and LogicRS232 Interface IR InterfaceIIC Interface Serial InterfaceThere are three 3 ports for receiving IR radiation. One 1 is located on the front of the projector just above the Green projection lens and the other two 2 are located on the rear panel. One of the receivers on the rear panel is located next to the LED display and, like the front receiver, is used for directly receiving IR radiation. The other rear-mounted receiver is used for connecting an IR repeater, which is an optional device that allows the user to control the projector from up to 150 feet away General I/OVideo Processor Board DescriptionInput DescriptionRaster Timing Generator DescriptionInput DescriptionVertical Deflection Board DescriptionInput DescriptionHorizontal Deflection Board Backplane Backplane Board p/nCRT Assembly Image Light Amplifier ILA Assembly2.7 Optical Section Relay Lenslight. The vertically polarized light then passes through the prism to the projector lens. The ILA assembly combines the input signal from the CRT with the high intensity light from the arc lamp. Thus, the brightness of the screen image does not depend on the brightness of the CRT but on the light from the xenon arc lamp. A more detailed explanation of the ILA assembly is in Section 2.8 at the end of this chapter CRT Image Combined Image and HighIntensity Light=Bright Image ScreenProjection Lens Arc Lamp AssemblyPrism 2.8 Image Light Amplifier Optical SubassembliesFigure 2-20 The Hughes-JVC Image Light Amplifier Figure 2-21 Simplified illustration of the Series 300 Projector optical path 3.0 Service Adjustments 3.1 Service Cover-Off Power-On SequenceContents Chapter 3---Service AdjustmentsMain AC Circuit Breaker 3.2 CRT Yoke Rotation 7. View R 3.3 Vertical Size Tracking 3.4 Vertical Linearity Tracking 3.5 Horizontal Size Tracking 3.6 ILA Bias Settings Note On Super Contrast Ila Assemblies3.7 CRT Mechanical Focus The lower-left rod adjusts the CRT to ILA distance z- axis 2. Increase Size to 100% horizontal and vertical 3.8 Electronic Focus 3.9 Jumper Settings Front/Rear JumpersR E A R p ro jectio n F R O N T p ro jectio nInverted Vertical Jumpers J300 J301 J500 J501J200 J201 J600 J400 J601Sensitivity/Threshold Offset 3.10 G2 AdjustmentG2 Setting To set G2 1. Cut off R and B and view G 3.11 Arc Lamp Alignment and Focus Model 330 Arc Lamp Alignment and FocusTo refocus the Model 330 Arc Lamp X-Axis Plate Z-Axis Screwplate Model 340SC and 370SC Arc Lamp Alignment and FocusY-Axis Plate 3.12 Arc Lamp Current Adjustment Figure 3-9. Model 340SC and 370SC Arc Lamp Adjustments2. Measure the number of millivolts between pins 3 and 4 on SPS J505 3-23 Chapter 3---Service AdjustmentsModel 330, 340SC, 370SC Service Manual 4.0 Maintenance Remove/Replace 4.1 IntroductionContents Model 330, 340SC, and 370SC Service ManualWARNING!!! Disconnect AC power from the projector before performing any removal and replacement proceduresFigure 4-1 Major components of the Model 330 Projector Chapter 4-MaintenanceModel 330, 340SC, and 370SC Service Manual Figure 4-2 Major components of the Model 340SC and 370SC Projectors Chapter 4-MaintenanceModel 330. 340SC, 370SC Service Manual 4.2 Projector Covers 4.3 Ventilation Filters4.4 Arc Lamp Assembly Model 330 Ignitor and Arc Lamp Assembly P/N 900611S RemovalJ503 and J504 Ignitor Assembly Wire Color Wire goes toIgnitor Location onStart Capacitor Squirrel Cage Fan Cable Interlock Switch Fan Connector Circuit BreakerJ503 J504 J505 Interlock Switch Lamp Current Adjust Collimating Condensing Lens Adjustment 3-mm Set Screw Mounting Screws4.5 System Power Supply AC Power Terminal Block Ground Main AC Circuit Breaker Mounting screws under lip4.6 Electronics Module 11. Replace the module in the reverse order 4.7 Cathode Ray Tube CRT Model 330 CRT Removal5. Remove the video amplifier board from the CRT Assembly Section Figure 4-10 Model 340SC and 370SC CRT Assembly Figure 4-11 CRT Z-Axis Focus Adjustment Rods circledChapter 4-Maintenance Model 330, 340SC, and 370SC Service ManualTo remove a VAB see Figure 4-9 or Figure 4.8 Video Amplifier Board VABModel 340SC and 370SC CRT Removal 4.9 CRT Yoke To remove the CRT yoke see Figure 4-9 or Figure4.10 High Voltage Power Supply HVPS 4.11 Card Cage Printed Circuit Boards 4.12 Image Light Amplifier Assembly 4.13 Projection Lens Lens Locking RodsChapter 4-Maintenance Model 330. 340SC, 370SC Service ManualTable 4-2 for reference to part numbers, if necessary 4-244.14 SCB Socket Battery Replacement CAUTION! Never place the socket battery on a metalLens Throw Lens Part Number or DesignationCAUTION! Never place the socket battery on 4.15 Recommended Spares DescriptionQuantity 340SCContents 5.0 Troubleshooting5.1 General Information Page 5.2 Power-On Codes Description Second SetCode 5.3 Break Points CodeMeaning DescriptionResetting the Projector Break Trap Data from the Diagnostics MenuCode Description5.4 Main Menu Structure Version 5.1.0 Software Menu DiagramChapter 5---Troubleshooting Model 330, 340SC, and 370SC Service ManualProblem and Possible SolutionService Symptom toProblem and Possible SolutionService Symptom toProblem and Possible SolutionService Symptom toProblem and Possible SolutionService Symptom toProblem and Possible SolutionService Symptom toProblem and Possible SolutionService Symptom toIntermittent Glossary of Terms Cold Mirror Test pattern of black-to-white gradation bars. The more levels Intensity Lumen Phase adjustment ResolutionRaster RetraceScan temporarily with the Executive I/R remote See Arc LampModel 330, 340SC, and 370SC Service Manual Glossary