Buffer Amplifiers
There are two buffer amplifiers that are used to supply buffered copies of the Y signal to other
uses. One,
is used to drive the rear panel Aux Y output. The other copy of the Y
signal is buffered by
and is used in the dynamic focus correction for beam position (see
FOCUS below).
X Deflection Amplifier
X Buffer Amplifiers
The X Deflection Amplifier and X Buffer Amplifier are identical to the Y Deflection Amplifier
and Y Buffer Amplifier described previously.
Intensity Control
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
for the axis signal that
comes from the wiper of the front panel intensity control. The output of
is used by the
brightness amplifier
and by the Focus Intensity Compensation Amplifier
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
This level corresponds to the dc level at the Control Gate Amplifier output that will be
translated to the CRT cutoff voltage by the
High Voltage Regulator board. R315 is
used to translate the voltage brightness signal from
into a current at the emitters of
Q305 and Q306 of the Blanking Switch CR303 is used to prevent the emitter voltage of
Q305 and Q306 from 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
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.
is used as a
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
Summary of Contents for 85662A
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Page 409: ...Table 4 Video Bandwidth Truth Table 6 A4A9 ...
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Page 452: ...A4A6A2 Output Driver Component Locations 85662 60170 Option 067 Tab ...
Page 453: ...A4A6Al Input Buffer Component Locations 85662 60171 Option 067 Tab ...
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Page 473: ...Table 4 Video Bandwidth Truth Table Option H96 3 ...
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Page 594: ...HEWLETT PACKARD HP Part No 85662 90085 Printed in USA ...