175A - HP Archive

Section IV
Paragraphs 4-47to 4-56
V205. When pressed, the switch reduces the gain so
that an unbalance prior to V204 and V205 cannot de-
flect the crt beam off the screen.
4-47. HIGH-VOLTAGE POWER SUPPLY.
4-48. The high-voltage supply provides the operating
voltages for the crt. A block diagram of the high-
voltage power supply is shown in figure 4-8. The
50-kc output of rf oscillator V301 is applied to high
voltage transformer T301. The transformer steps
up the oscillator output to high ac voltages which
rectifiers V304, V305, and doubler stage V302 and
V303 convert to dc. The dc voltages are then sup-
plied to the crt.
4-49. Control of the high-voltage supply is accom-
plished by comparing the -2700 volts supplied to the
crt cathode with +370 volts from the regulated low-
voltage power supply. Changes in the -2700 volt sup-
ply produce an error voltage which is amplified by
the dc control amplifier V306A-B and is applied to
the oscillator as a control voltage. The control volt-
age changes the output amplitude of the oscillator,
and hence corrects for the change in the -2700 volt
supply.
4-50. The crt is normally biased off. The positive
unblanking gate from the sweep generator, applied
to the crt control grid, overrides the bias and un-
blanks the crt. The gating pulse time is identical to
the sweep time so that the crt remains onduring
sweep time and external horizontal operation.
fi- REGULATOR
I
4- 51. INTENSITY CONTROL.
Model 175A
4-52. INTENSITY control R319 varies the voltage
applied to the control grid of the crt, and FOCUS con-
trol R334 varies the voltage applied to the focusing
anode of the crt. The ASTIGMATISM control, R340
varies the voltage on the astigmatism lens (anode) of
the crt to compensate for electron-beam defocusing
when the beam is deflected. A section of the BEAM
FINDER push button switch is in the crt control-grid
supply circuit. When depressed, the switch returns
the grid supply to +370 volts, thus decreasing grid
bias voltage and turning on the crt.
4- 53. TRACE ALJGNMENT CONTROL.
4-54. TRACE ALIGNMENT control R350 rotates the
trace by varying the current through a coil around the
neck of the crt, and hence the magnetic field through
which the beam must pass. Rotation of the TRACE
ALIGNMENT control changes the voltage and polarity
across the deflection coil enough to give a control
range of approximately A0 degrees.
4-55. LOW-VOLTAGE POWER SUPPLIES.
4-56. The low-voltage power supplies include an in-
dependent supply and three dependent supplies. The
-100 volt supply is the independent supply. It is a
reference for the +370 and +110 volt supplies and
provides operating voltage to the differential ampli-
fier of the +110 volt supply and to the sensor ampli-
fier of the +6.3 volt supply.
+370V
+
RECTI F I ER -2700V
TO CRT
CATHODE
I I
- 2900V
OSCl LLATOR RECTIFIER TO CRT
TRANSFORMER
CONTROL
GRID
RECTIFIER
DOUBLER
4
1711--8-6
Figure 4-8. High-Voltage Power Supply Block Diagram
+9300V
TO CRT
ACCELERATING
ELECTRODE
4- 6 01526-2