JVC 250 Service Manual

Contents

Chapter 3---ElectricalModel 250 Service Manual 3-11RGB Anode Voltage - goes directly to each CRTRGB Focus Voltage - goes directly to each CRTArc Ground - The Arc Ground protection for each CRT from the Video AmplifierPCB.HVPS - OperationThe High Voltage Power Supply has three basic functions.! High Voltage Generation! Focus Voltages! High Voltage and CRT ProtectionHigh Voltage Generation - The High Voltage Amplifier section converts the +80V from the Low Voltage Power Supply, to 25 kV, and divides it into three outputsfor each CRT. It also uses the HVPS_SYNC signal from the Raster TimingGenerator PCB. This signal is synchronized to the horizontal sync to eliminateone source of moving noise on the screen. The High Voltage section also suppliesthe G2 Voltage for the Video Amplifier PCB.Focus Voltages - The High Voltage Power Supply receives the horizontal andvertical parabolas from the Convergence Deflection PCB and adds them together.They are amplified and sent to the Focus Pack section. The Focus Pack sectioncouples the amplified parabola waveforms to the Focus Voltages. The Focus Packdivides the Focus Voltage into three signals and outputs each signal to a CRT.The DC Focus Voltages are manually adjusted as necessary.The Arc Ground signal goes to the Video Amplifier PCB and from there, connectsto the CRT. It provides a direct return path for arc currents in the event of internalCRT arcing.High Voltage and CRT Protection - The High Voltage Power Supply receives a/HV_ENA (/VA_OK) signal from the Video Amplifier PCB. This signal goes tothe Protect OR section. The Protect OR section also checks the incoming +80 V.from the LVPS for an overcurrent condition. The Protect OR section alsomonitors the high voltage output for an overvoltage condition. If any of thesechecks shows a problem the Protect OR section shuts down the high voltageamplifier. The Protect OR section outputs the /HV_OK signal telling the SystemController PCB that the High Voltage Power Supply is functioning properly.HVPS - Service AdjustmentsNormally, the only High Voltage Power Supply adjustments are for CRT Focus.The CRT Focus Voltage adjusts are mechanical potentiometers located on theside of the High Voltage Power Supply (see Figure 3-5) that adjust the focus foreach CRT. The CRT Focus Voltage adjustments are detailed in the CRT Section(see section 5.10 CRT/Yoke Assemblies).