Tektronix 2215A, Инструкция по эксплуатации

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Theory of Operation— 2215A Service
Figure 3-5. Simplified diagram of the Dc Restorer circuitry.
During the positive transitions of the ac drive, from the
lower clamped level toward the higher clamped level, the
charge on C854 increases due to the rising voltage. The
voltage increase across C854 is equal to the amplitude of
the positive transition. The negative transition is coupled
through C854 to reverse bias CR854 and to forward bias
CR855. The increased charge of C854 is then transferred to
C855 as C854 discharges toward the Z-Axis output level.
Successive cycles of the ac input to the Dc Restorer will
charge C855 to a voltage equal to the initial level plus the
amplitude of the clamped square-wave input.
The added charge on C855 determines the control-grid
bias voltage. If more charge is added to that already present
on C855, the control grid becomes more negative and less
crt writing-beam current will flow. Conversely, if less charge
is added, the control-grid voltage level will be closer to the
cathode-voltage level and more crt writing-beam current
flows.
During periods that C854 is charging, the crt control-grid
voltage is held constant by the long time-constant discharge
path of C855 through R860.
Fast-rise and fast-fall transitions of the Z-Axis output sig­
nal are coupled to the crt control grid through C855 to start
the crt writing-beam current toward the new intensity level.
The Dc Restorer output level then follows the Z-Axis output-
voltage level to set the new bias voltage for the crt control
grid.
Neon lamps DS858 and DS856 protect the crt from ex­
cessive grid-to-cathode voltage if the potential on either the
control grid or the cathode is lost for any reason.
POWER SUPPLY AND PROBE ADJUST
The Power Supply circuitry converts the ac power-line
voltage into the voltages needed for instrument operation. It
consists of the Power Input, Preregulator, and Inverter cir­
cuits (which drive the primary of the power transformer) and
secondary circuits (which produce the necessary supply
voltages for the instrument).
Power Input
The Power Input circuit converts the ac power-line volt­
age to filtered dc for use by the Preregulator.
POWER switch S901 connects the ac power line through
fuse F9001 to the bridge rectifier composed of CR901,
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