User's Manual

The

Beam Current Buffer converts the, high impedance low current, beam

current signal into a low impedance voltage. This voltage is applied to the auto

bias IC through a 200 ohm resistor. After the three lines of beam current are

measured, the program pulse from the auto bias IC, produces a voltage drop

across this 200 ohm resistor that equals the amplitude of the beam current

voltage.

Refer to the block diagram on page 15 (foldout) when reading this description.

The Video Interface is designed around a custom IC and will accept DC or AC

coupled positive analog video signals. It can also be used with negative analog

and 4 line TTL. This IC has a built in multiplier circuit for the master gain

control and blanking functions. Resistors are used to protect the IC and to set

the gain. The programmed gain is dependent on the input signal amplitude

except with the TTL mode. Solder jumpers and component substations are used

to program the Video Interface for the type of input signal to be received. The

output of the IC drives the video amplifiers. This drive is a current where 0 mA

is black and 10 mA is a saturated color.

The Video Amplifiers are of the push pull type. They are built partly on thick

films and partly on the video PCB. Spreading out the amplifier reduces the

component heat and improves the life of the unit. The bandwidth is 25 MHz with

40Vp-p output. The rise and fall times are 20nS.

The Beam Current Feedback circuit directs most of the beam current of each

amplifier to the beam current buffer. The only time this current is measured, by

the auto bias circuit, is during the time of the three faint lines at the top of the

screen and three lines thereafter. The CRT auto bias circuit is designed to adjust

the video amplifier bias voltage such that the beam current of each of the three

guns is set to a specific programmed value.