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MODEL
8559A
SERVICE
SW
l
TCH
I
@SWEEP
DEAD
TIME SWITCH
7&6
I
I
FIGURE
8
-
35.
SIMPLIFIED SCHEMATIC OF FASTISLOW SWEEP TIME OPERATION
FastlSlow Sweep
Time
Operation
Timing capacitors C3 and C4 provide fast and slow sweep operation (refer to Figure 8-35). When a sweep time
less than or equal to 1 millisecond per division is selected with the SWEEP
TIME/DIV switch, sweep control
line ST6 is grounded. This turns sweep dead time switch
46 (block
K)
and fast sweep switch
47
(block
J)
off.
With
47 off, C3 and C4 are in series; C4 effectively becomes the timing capacitor. With 46 off,
+
15V at
R46
reverse biases CR9 and CR8, switching C10 out of the dead time circuit. Capacitor C11 now sets a short dead
time of about 0.4 millisecond.
In sweep times greater than or equal to 1 millisecond per division or in automatic sweep, control line ST6 is
open, turning both Q6 and
47 on. Transistor 47 grounds C3 and it becomes the timing capacitor. Transistor
46
forward biases CR8 and CR9, paralleling C10 and C11. The dead time is effectively established by C10 at about
8.0 milliseconds.