JVC 250 service manual Video Processor PCB - Remove and Replace

Chapter 5---Electronics

The G2 voltage accelerates the electrons that are emitted from the cathode of the CRT. The CRT filament emits the electrons and G1 voltage regulates the amount of electrons that are emitted from the cathode. The G2 voltage is adjusted through the menu (Black Level). The Video Processor PCB receives the G2 control data for each color through the IIC bus and sends an analog voltage to the Video Amplifier PCB to control the G2 voltage.

The Video Processor PCB protects the CRTs from excess beam currents to prevent it from burning the phosphor. The Video Amplifier PCB sends a sample of the beam current (RGB_BEAM) for each CRT back to the Video Processor PCB. The Video Processor PCB compares this sample to a preset value. If the sample beam current is higher than the preset value, the Video Processor PCB reduces the contrast for the CRT with high beam current. If the CRT beam current is still high, it then reduces the G2 voltage. The maximum beam current is 250 µA per CRT.

The Video Processor PCB receives the G1_BIAS signal from the System Controller PCB through the IIC bus and sends a voltage to the Video Amplifier PCB to set the brightness level.

Figure 5-9Video Processor PCB LEDs.

Video Processor PCB - Remove and Replace

Tools Needed

#1 Pozi-drive Phillips-head screwdriver

Parts Needed

Video Processor PCB - p/n 105234

To remove the System Controller PCB:

1.Power off the projector by IR Remote or PC, and allow the cooling fans to run until they shut off automatically.

2.Turn the AC Circuit Breaker to the OFF position and unplug the AC Power Cord.

3.Disconnect all the external source video cables and control cables.

4.Remove the rear cover.

5.Remove the Back Panel by removing the nine Pozi-drive Phillips-head retaining screws using the #1 Pozi-drive Phillips screwdriver.

Model 250 Service Manual 5-15