Principles Of Operation; Introduction; Block Diagram Discussion; High Voltage Power Supply - HP 1317A Operating And Service Manual

Model 1317A
Theory
SECTION IV
PRINCIPLES OF OPERATION
4-1. INTRODUCTION.
4-2. This section contains function descriptions of
Model 1317 A, keyed to an overall block diagram.
The block diagram and schematics are located in
Section VIII.
4-3. BLOCK DIAGRAM DISCUSSION.
4-4. This discussion illustrates the function of each
circuit group (block) and the relationship of the
blocks to each other. It is based on the overall block
diagram, figure 8-2. The conditioning and calibrating
controls, as shown on the block diagram, illustrate
the association of the control with a particular block
and are not necessarily an accurate representation of
the control's action.
4-5. LOW VOLTAGE POWER SUPPLIES.
4-6. This block (All) provides operating power to
all the other blocks, including the high voltage power
supply and some of the CRT elements. Three regu-
lated dc outputs are provided: +250 V, +15 V, and
-15 V. The +250 V supply and the -15 V supply are
adjustable. The +15 V supply is referenced to the
-15 V supply. Several other voltages are derived from
the +250 V supply by means of voltage dividers and
avalanche diodes. Additionally, an unregulated dc
output to the high voltage oscillator and a 6.3 Vac
output to the CRT filament are provided.
4-7. HIGH VOLTAGE POWER SUPPLY.
4-8. The high voltage power supply (on A12 and
A13)
provides the high operating potentials for the
CRT. The rf output of the high voltage oscillator is
stepped up by the high voltage transformer and con-
ditioned by the other components on A12. A sample
of the high voltage output drives the error detector.
The error detector controls the conduction angle of
the high voltage oscillator to accomplish regulation.
4-9. DEFLECTION SYSTEM.
4-10. The X-axis amplifiers (on Al and A2) and the
Y-axis amplifiers (on A3 and A4) are identical. They
drive the horizontal and vertical deflection plates of
the CRT proportionally to the signals applied to the
X INPUT and Y INPUT.
4-11. FOCUS AND ASTIGMATISM CIRCUITS.
4-12. Samples from the X and Y amplifiers, pro-
portional to the CRT beam position, drive the focus
and astigmatism circuits (on A6). These circuits
develop correction voltages for the focus and astig-
matism elements of the CRT. The astigmatism
element is directly controlled by the output of the
astigmatism driver. The focus element is connected
to the -3400 V output of the high voltage power
supply. This supply is returned to (and controlled
by) the output of the focus driver. The focus driver
also receives a sample from the Z-axis amplifier and
causes focus corrections for changes in beam inten-
sity.
4-13. PHOSPHOR PROTECTION CIRCUITS.
4-14. The phosphor protect control circuits (on Al
and A3) detect static or slow moving deflection
voltages and activate the phosphor protection circuit
(on A5). The phosphor protection circuit limits the
output of the Z-azis amplifier and protects the CRT
mesh and phosphor from damage that a static, high-
intensity beam could cause.
4-15. Z-AXIS AMPLIFIER.
4-16. The high voltage supply for the CRT control
grid is returned to (and controlled by) the output of
the Z-axis amplifier (on A6). Consequently, the volt-
age applied to the Z INPUT controls CRT beam
intensity. The Z-axis amplifier can be switched to
permit blanking by either a positive or negative
voltage at the Z INPUT.
4-17. CIRCUIT DETAILS.
4-18. PHOSPHOR PROTECT CIRCUITS. Phosphor
protect circuits in the X axis and Y axis are identical
in operation so only the X-axis circuits will be describ-
ed (schematics 1 and 2).
4-19. Excessive intensity caused by a slow-moving
or static beam can cause damage to the CRT ex-
pansion mesh or phosphors. When deflection speeds
are reduced to a potentially harmful level (less than
approximately 76 mm/ ms (3 in.!ms), the phosphor
protect circuits limit CRT cathode current. This
current limiting action occurs because of circuit
actions described below.
4-20. Differential output, from the X-axis voltage
differential amplifier stage (schematic 1), is applied to
X-axis emitter follower stage (schematic 2). Differ-
ential output of this stage is proportional to the beam
position in the X-axis direction, and is applied to the
voltage sensor stage. A voltage change at the col-
lector of either voltage sensor reduces the voltage on
A1C19. When the voltage on
A1C19
is sufficiently
reduced, the phosphor protect control is activated and
produces a positive voltage at its output.
4-1