JVC 250 service manual Convergence Deflection PCB - Operation

Chapter 5---Electronics

Figure 5-21Physical layout of the Convergence/Deflection PCB.

Convergence Deflection PCB - Operation

The Convergence Deflection PCB performs four main functions. It generates the vertical deflection sawtooth waveform. It generates the square waves that bias the three ILA® s. It controls the amplitude of waveforms used for convergence corrections, and it generates the parabolic waveform used for dynamic focus.

The Convergence Deflection PCB receives the V_DRIVE signal, which is a sample of the vertical sync, from the Raster Timing Generator PCB. The Convergence Deflection PCB has a Waveform Generator Section that generates the vertical deflection sawtooth waveform and outputs the V_RAMP signal that drives the vertical amplifier on the Horizontal Vertical Deflection PCB. The vertical amplifier drives the CRT deflection coils for vertical deflection. The Waveform Generator also generates the parabolic waveforms used for geometry correction such as bow, pincushion, keystone, and linearity

Each of the ILA® s is biased by a square wave generated by the Waveform Generator on the Convergence Deflection PCB. Each ILA® is biased separately through the ILA® Bias command in the Factory Adj. Menu. The commands are received through the IIC interface. As the square wave that drives the ILA® is increased, the ILA® becomes more sensitive to the image light that strikes the photoconductive layer and outputs more light. The command that controls the frequency of the ILA® bias square wave is referred to as ILA® Sensitivity. It is a global command for all the ILA® s and is received from the IIC interface.

Attached to the green ILA® mount is a thermistor that senses the temperature of the ILA® . It sends the Convergence Deflection PCB a signal that adjusts the green ILA® bias to compensate for temperature variations inside the projector. If the

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