HP 3585A Service Manual page 215

Circuit Functional Descriptions
Now for the alphanumerics. An 8-bit DAC receives information that determines the y-axis
point about which the character will be formed. A 3-bit DAC receives the dot matrix infor­
mation for the y-axis. The y-axis Graphics DAC receives the information for determining
the x-axis position of the character and the X Matrix DAC determines the x-axis dot matrix
position.
All of the display information reaches the analog switch where the analog signals are con­
trolled so that the proper information reaches the display at the correct time. This informa­
tion is buffered and sent on to the A67, XYZ board. These signals also go to the rear panel
for an external display.
The A67 board is the XYZ board and is basically the amplifiers necessary to raise the signals
from the A64 board to the levels needed by the CRT. A 1 00 volt regulator power supply pro­
vides voltage necessary for the deflection amplifiers. The x-axis and y-axis amplifiers are
identical. A differiential circuit provides complementary outputs which are amplified to
levels necessary for the CRT deflection plates.
Since the line intensity is controlled on the A64 board, the z-axis signal is an on/off signal.
That is, blanking occurs during retraces and between dots of the matrix when the character
is being drawn. The z-axis signal enters the A67 board, is amplified, and then is sent to the
A65 board where it causes blanking and unblanking.
The high voltage oscillator consists of the A65, A66 and part of the A67 boards. The HV
oscillator stimulates the primary of the HV transformer with a 20 to 30 kHz signal. The
highly stepped up signal from the secondary of the HV transformer is rectified and filtered
by the Pi network filter thus providing a -4000 Vdc cathode voltage. This voltage is sampled
by the feedback network to regulate the dc level of the base winding of the HV transformer
thus maintaining a cathode voltage of -4000 V dc.
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Scans by ART EK MEDIA =>
Model 3585A