JVC 330, 370 SC, 340 SC service manual ILA Bias, Dynamic Focus Amplifier

Chapter 2—Functional Descriptions

Video signal cutoff is accomplished by pulling blanking to zero.

ILA® Bias

ILA® Assembly biasing is accomplished by generating a pseudo-square-wave with frequency set by the operator. The SCB sends the information on bias frequency via the IIC interface to the VPB. The operator can control the frequency over a range of from 1.5KHz to 3.0KHz. Selecting ILA BIAS FREQ from the ILA SETUP menu under the MAIN MENU controls the frequency. The bias square wave is phase locked to the vertical sync to prevent any moving artifacts from occurring on the screen due to bias.

The bias square wave is passed through an amplifier whose gain is set by the operator via the SCB to vary the bias. This square wave is then turned into a differential output in order to eliminate DC going to the ILA® Assemblies. The outputs can be monitored at TP11 and 12 (RED), 1 and 14 (GRN), and 15 and 16 (BLU). Selecting BIAS W/O VIDEO from the ILA SETUP MENU under the Main Menu controls the bias level for each individual color. The up and down arrows are then used to vary the bias level.

Dynamic Focus Amplifier

The vertical focus amplifier takes the VPARAB signal from the VDB, amplifies it and sends it out to the HVPS as the signal VDFOCUS for vertical dynamic focus. The HPARAB signal, from the VDB, is multiplied by the VPARAB signal, amplified, and also sent out to the HVPS as the signal HDFOCUS for horizontal dynamic focus.

Serial Communication

The VPB uses two (2) separate, interrelated serial data communication systems to communicate with the SCB; the IIC bus, and a differential, synchronous data bus. The information transferred over the serial busses is indicated below (I = input to VPB, O = output from VPB). Also noted is whether the information is transferred over the IIC or the serial bus. A change in output data generates an interrupt pulse.

Table 2-10VPB Serial BUS Information

BUS	I/O	Information	Description
IIC	I	RENABLE	Signal to cut off red.
IIC	I	GENABLE	Signal to cut off green.
IIC	I	BENABLE	Signal to cut off blue.
IIC	I	CH1SEL	Selects RGB1 as input.
IIC	I	CH2SEL	Selects RGB2 as input.
IIC	I	ILA® bias freq	Information for setting bias frequency to ILA®
			Assembly.
IIC	I	SLOAD	Command to the serial data receiver that the
			incoming data is to be read.

2-48 Model 330. 340SC, and 370SC Service Manual