JVC 250 service manual HVPS - Operation, HVPS - Service Adjustments

Chapter 3---Electrical

RGB Anode Voltage - goes directly to each CRT

RGB Focus Voltage - goes directly to each CRT

Arc Ground - The Arc Ground protection for each CRT from the Video Amplifier PCB.

HVPS - Operation

The High Voltage Power Supply has three basic functions.

!High Voltage Generation

!Focus Voltages

!High Voltage and CRT Protection

High Voltage Generation - The High Voltage Amplifier section converts the +80 V from the Low Voltage Power Supply, to 25 kV, and divides it into three outputs for each CRT. It also uses the HVPS_SYNC signal from the Raster Timing Generator PCB. This signal is synchronized to the horizontal sync to eliminate one source of moving noise on the screen. The High Voltage section also supplies the G2 Voltage for the Video Amplifier PCB.

Focus Voltages - The High Voltage Power Supply receives the horizontal and vertical parabolas from the Convergence Deflection PCB and adds them together. They are amplified and sent to the Focus Pack section. The Focus Pack section couples the amplified parabola waveforms to the Focus Voltages. The Focus Pack divides 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, connects to the CRT. It provides a direct return path for arc currents in the event of internal CRT 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 to the Protect OR section. The Protect OR section also checks the incoming +80 V. from the LVPS for an overcurrent condition. The Protect OR section also monitors the high voltage output for an overvoltage condition. If any of these checks shows a problem the Protect OR section shuts down the high voltage amplifier. The Protect OR section outputs the /HV_OK signal telling the System Controller PCB that the High Voltage Power Supply is functioning properly.

HVPS - Service Adjustments

Normally, the only High Voltage Power Supply adjustments are for CRT Focus. The CRT Focus Voltage adjusts are mechanical potentiometers located on the side of the High Voltage Power Supply (see Figure 3-5) that adjust the focus for each CRT. The CRT Focus Voltage adjustments are detailed in the CRT Section (see section 5.10 CRT/Yoke Assemblies).

Model 250 Service Manual 3-11