HP 85662A, Troubleshooting And Repair Manual

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Fast Sweep Control
The Fast Sweep Control contains circuitry for end of sweep detection and controls fast sweep
dead time, and fast sweep triggering.
End of Sweep Detection
When the sweep ramp reaches about V, conducts and turns Q4 on. When the
collector of Q4 goes low, pin 5 produces a whose length is the dead time.
and are cleared when pin 5 goes low, and timing capacitors C4 and C5 are
discharged by the Discharge Switch in the Fast Sweep Generator. Voltage divider and
R20 set the level at which Q5 senses the end of the sweep ramp. (Note that the fast sweep
ramp ends beyond the right-hand edge of the CRT.) The LRTRC line from pin 5, which
is high during the sweep, supplies the retrace blanking signal to Intensity Control.
Fast Sweep Dead Time
Multivibrator controls the sweep dead time. is triggered at the end of the fast
sweep ramp and holds and cleared for a time that is determined by C7, R24, and
R25. This prevents the triggering of further ramps for the length of the pulse from pin
5. The length of the dead time is about 15 for sweep times from 1 through 100 and
about 120 for sweep times from 200 through 10 ms. The ST 100 (from U6 pin 12 in
the Fast Sweep Time Control circuit) controls the length of the sweep dead time by switching
the
timing resistors with transistor switch Q3. In sweep times of 10 ms through 200
Q3 is off and the dead time, set by C7 and R24, is 120 In sweep times of 100 through
1
Q3 is on, placing R25 in parallel with R24 to decrease the dead time to 15 C6 and
R23 supply additional base drive to Q4 at the end of the sweep to insure triggering of
Fast Sweep Triggering
Flip-flops and control the state of the fast sweep generator. controls the
Discharge Switch through At the end of a fast sweep, both and
are held cleared by the dead time circuit and Following the dead time,
a trigger from U16 pin 5 causes pin 7 to go low. This causes pin 5 to go high,
which turns off the Discharge Switch and starts a sweep ramp. This can occur only if FS EN
is high. If FS EN is low, the J and K inputs of are held low and a trigger not set
Fast Sweep Multiplexing
In Fast Sweep mode, the X output of Line Generator and the fast sweep ramp must
be multiplexed to X Deflection Amplifier or XYZ Driver Amplifier to produce a
display consisting of the graticule and characters with the fast sweep ramp and the analog
video signal. The video from Video Processor is multiplexed to Y
Deflection Amplifier or XYZ Driver Amplifier when the fast sweep ramp is multiplexed
to or The X and Y multiplexers are located in Intensity Control.
In Fast Sweep mode, the output from is applied to the CRT deflection amplifiers
following the completion of at least one fast sweep ramp.
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