Power Supply And Probe Adjust - Tektronix 2215A Instruction Manual

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Theory of Operation— 2215A Service

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

3-16

Figure 3-5. Simplified diagram of the Dc Restorer circuitry.

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.

cessive grid-to-cathode voltage if the potential on either the

control grid or the cathode is lost for any reason.

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

age to filtered dc for use by the Preregulator.

fuse F9001 to the bridge rectifier composed of CR901,

Neon lamps DS858 and DS856 protect the crt from ex