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Chapter 2—Functional Descriptions
2-48 Model 330. 340SC, and 370SC Service Manual
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 2-10
VPB 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.