Theory of Operation
Theory of Operation
3Ć12
The Vertical Yoke Winding Driver provides the scan current (ramp) for the
vertical (field) deflection coil. A vertical sync signal, a negative pulse at the
deflection rate, causes the ramp to retrace" to the top of the CRT screen.
A large pulse is generated during vertical retrace. A portion of this signal
drives the G1 grid 50 V more negative than normal during the retrace period.
This keeps retrace lines blanked even when the background is visible.
The Video Amplifier amplifies the input video signal, and drives the cathode
of the CRT.
Horizontal Deflection, CRT, and High VoltageĂA26Ă
2
The Horizontal Oscillator Control generates the switch" controlling signal
and synchronizes the scan to the horizontal sync input signal. IC U370
includes a horizontal oscillator, a phase detector, and an output shaper.
The circuit is a phaseĆlocked loop. The differentiated horizontal sync is the
reference signal, and the retrace or flyback pulse (U370 pin 4) is the
feedback signal to be locked to the horizontal sync (HORIZONTAL YOKE)
signal.
Horiz Yoke Winding Driver transistor Q160, along with Q260 and T170,
provides the deflection coil currents.
Transformer T210 generates the CRT high voltage from the large voltage
pulse that occurs during horizontal retrace (flyback pulse). Other secondary
voltages are also derived from the flyback pulse.
The fan provides forced air cooling for the oscilloscope. It connects to a 12 V
connector on the Low Voltage Power Supply.
Fan
