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Buffer Amplifiers @)
There are two buffer amplifiers that are used to supply buffered copies of the Y signal to other
uses. One, UlOlB, is used to drive the rear panel Aux Y output. The other copy of the Y
signal is buffered by UlOlA and is used in the dynamic focus correction for beam position (see
FOCUS below).
X Deflection Amplifier NJ, 8, @
X Buffer Amplifiers @
The X Deflection Amplifier and X Buffer Amplifier are identical to the Y Deflection Amplifier
Intensity Control @, 0, @
The intensity section takes brightness information from the line generator section (A3) of the
machine and provides analog modulation of the CRT and digital blanking.
Brightness @ provides a high impedance input buffer (U401B) for the 2 axis signal that
comes from the wiper of the front panel intensity control. The output of U401B is used by the
brightness amplifier (U401D) and by the Focus Intensity Compensation Amplifier @J U4OlC.
The pot R319 is used to set the analog gain of the intensity amplifier. This adjustment is used
to calibrate the brightness of the CRT using a known test pattern and a light meter. R316,
R318, and R319 set the gain of the amplifier, while R317 is used to set the output offset. This
offset is used to set the overall minimum analog output level of the Control Gate Amplifier
translated to the CRT cutoff voltage by the AlA High Voltage Regulator board. R315 is
used to translate the voltage brightness signal from U401D into a current at the emitters of
Q305 and Q306 of the Blanking Switch 0. CR303 is used to prevent the emitter voltage of
Q305 and Q306 f rom going positive during turn on and damaging the base emitter junctions.
The Blanking Switch @ consists of a differential pair current switch, Q305 and Q306. The
base of Q305 is biased at -1.9 V by R309 and R310. The base of Q306 is driven from a TTL
signal (BLANK, low = dark) that is translated down in voltage by R311, R312, and R314
such that the signal at the base will swing either side of the -1.9 volt level on the other side
of the differential pair. The result is that when BLANK is low, Q305 will be on, Q306 will be
off, and the brightness current signal from R315 will be drawn through the collector of Q305
from ground. No current will be drawn from the input of the current to voltage amplifier.
When BLANK is high, Q306 will be on and Q305 will be off. C305 is used as a speedup. In
this case the brightness current signal from R315 will be drawn through the collector of Q306
from the virtual ground input of the current to voltage amplifier.
R329 is used to set a minimum current draw at the input of the current to voltage amplifier to
set the minimum output voltage level when the brightness signal is blanked.
4 AlA
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