Saw-Tooth Wave Signals And Waveform Correction Circuit (U501); Vertical Output Amplifier Circuit (U401); High Voltage Circuit; Dynamic Focus Circuit - Mitsubishi Diamond Pro 750SB Service Manual

3.3.2 Saw-tooth Wave Signal and Waveform Correction Circuit (U501)
1) Vertical oscillator
When a vertical sync signal input is entered into U501 Pin 14, the saw-tooth wave signals are output from
U501 Pin 12 and 13. The frequencies of these waveforms are identical with those of the vertical input sync
signal. If there is no vertical sync signal input, the frequency of the output waveform is equal to the
free-run frequency. This free-run frequency is maintained at approximately 75Hz.
2) Vertical size control circuit
The saw-tooth wave signal output generated from U501 Pin 12 and Pin 13 is input to U401 of the vertical
output amplifier. The vertical screen size is controlled by changing the amplitude of this saw-tooth wave
signal.
3) Vertical raster position
The saw-tooth wave signal output generated from U501 Pin 12 and 13 is input to U401 of the vertical
output amplifier. At the same time, the DC component of the waveform applied to U401 Pin 7 changes to
control the vertical raster position.

3.3.3 Vertical Output Amplifier Circuit (U401)

The saw-tooth wave signal output generated from U302 Pin 12 is input to U401 Pin 1 of the vertical output
amplifier. The amplified current waveform is output from U401 Pin 5. With this current, the vertical deflection
coil is operated.

4. High Voltage Circuit

The high voltage circuit uses the PWM control system to regulate the ON/OFF time of the high voltage
generator FET. U301 is the IC that performs the PWM control. The pulse voltage generated in Q305 is
stepped up at T301 (F.B.T.) to obtain a 26kV potential. The feedback voltage from T301 Pin 11 is divided by
a combination of R316 and VR301, and the obtained voltage is then fed back to IC701 Pin 1. A constant high
voltage is maintained by controlling the pulse width of the PWM output at Pin 10. For the adjustment of a high
voltage the VR301 is adjusted, which is used as a shunt resistor of the feedback voltage. The PWM output is
synchronized with the horizontal sync frequency. The trigger pulse signal for synchronization is output from
the shunt voltage of the collector pulse obtained from the horizontal deflection output circuit Q314. This
output is applied to IC301 Pin 5.

5. Dynamic Focus Circuit

The primary winding of T302 is driven by the parabolic voltage generated by the horizontal source +B circuit.
As a result, a step-up horizontal parabolic waveform is generated in the secondary winding of T302. On the
other hand, the vertical parabolic waveform output is generated from IC501 Pin 32 and it is then amplified at
Q312. The vertical parabolic waveform signal is superposed on the horizontal parabolic waveform signal
available on the secondary side of T302. The power supply for Q312 is obtained by using the output voltage
at T301 Pin 6 Which is rectified by D307 and C311.
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